Biochemistry MCQs for NEET PG
921 worked Biochemistry questions across 178 areas. Each one has its own page with the reasoning for every option.
What this set is
Biochemistry splits into metabolism, molecular biology and clinical correlations. The highest-return habit is linking each enzyme deficiency to the disease, its inheritance and its signature finding.
This page lists the 921 Biochemistry questions that have a full worked page: 678 application questions that put a fact to use on a patient or a finding, and 243 multi-step questions that combine two or more ideas. Plain one-fact recall items are left out here on purpose. The Biochemistry practice bank in the app is larger, with 3,709 questions in all, and is where timed tests and daily practice draw from.
How to use it
- Pick an area you are weak in, below.
- Answer first, then read why each wrong option fails.
- Write a three-line note for every miss, and revisit it in a week.
- Move to a timed Biochemistry test once an area feels steady.
These are original practice items, not recalled exam questions, and they are not yet reviewed by independent faculty. Confirm important facts in a standard textbook.
What Biochemistry covers in the exam
- Biomolecules and enzymes
- Carbohydrate metabolism
- Lipid metabolism
- Amino acid metabolism
- Nucleotide metabolism
- Vitamins and minerals
- Molecular biology and genetics
- Clinical biochemistry
A study map from the standard curriculum; the NBEMS bulletin is the authority. See the Biochemistry study guide.
Worked questions by area
178 areas, largest first. Open an area to see its questions.
Amino acid metabolism86
- Amino acid metabolism · ApplicationA baby has a mousy odour, fair skin and developmental delay. Which enzyme is deficient?
- Amino acid metabolism · ApplicationClassic phenylketonuria is caused by deficiency of which enzyme?
- Amino acid metabolism: branched-chain · ApplicationA 7-day-old breastfed neonate becomes lethargic and feeds poorly, and has a sweet, maple syrup odour in the urine and ketonuria. Which enzyme complex is defective?
- Amino acid metabolism: tyrosine · ApplicationA 45-year-old man has arthritis of the spine and knees, bluish-black discolouration of the ear cartilage and urine that turns dark when left standing. Which enzyme is d…
- Amino acid metabolism: homocystinuria · ApplicationA 14-year-old tall boy with long thin limbs, intellectual disability and downward dislocation of the lens develops a deep vein thrombosis. Which combination of plasma f…
- Amino acid metabolism: tyrosinaemia type I · Multi-stepA 5-month-old infant has failure to thrive, hepatomegaly, a bleeding tendency with prolonged prothrombin time, rickets and a cabbage-like odour. Urine contains succinyl…
- Amino acid metabolism: glycine cleavage system · ApplicationA 3-day-old neonate has hiccups, profound lethargy, hypotonia and myoclonic seizures, with a high CSF to plasma glycine ratio and normal blood ammonia and urine organic…
- Amino acid metabolism: ammonia and the brain · Multi-stepA man with decompensated cirrhosis has confusion and a flapping tremor with a blood ammonia level three times normal. Which process in the brain contributes most to the…
- Amino acid metabolism: glucose-alanine cycle · ApplicationDuring a 48-hour fast, skeletal muscle breaks down protein and releases large amounts of alanine into blood. What is the main biochemical purpose of this release?
- Amino acid metabolism: pyridoxal phosphate · ApplicationA 40-year-old malnourished man on a regimen containing isoniazid develops numbness and tingling of both feet. Which biochemical change underlies this neuropathy?
- Amino acid metabolism: glutathione · ApplicationA 20-year-old woman presents 6 hours after ingesting about 30 tablets of paracetamol. Intravenous N-acetylcysteine is started. What is its biochemical basis?
- Amino acid metabolism: tetrahydrobiopterin deficiency · Multi-stepA 4-month-old infant has high blood phenylalanine and was started on a low phenylalanine diet, with phenylalanine falling to normal. However, the child has progressive…
- Amino acid metabolism: catecholamine synthesis · ApplicationA 45-year-old man with a biochemically proven pheochromocytoma is given metyrosine before surgery to reduce catecholamine production. Which enzyme does it inhibit?
- Amino acid metabolism: primary hyperoxaluria · ApplicationA 6-year-old child has recurrent flank pain, haematuria and calcium oxalate stones, with nephrocalcinosis on ultrasound. Urinary oxalate and glycolate are raised. A def…
- Amino acid metabolism: propionic acidaemia · Multi-stepA 4-day-old breastfed neonate has vomiting, poor feeding and lethargy, with high anion gap metabolic acidosis and hyperammonaemia. Urine organic acid analysis shows 3-h…
- Amino acid metabolism: hyperammonaemia treatment · ApplicationA 3-day-old neonate with a suspected urea cycle disorder has a plasma ammonia of 900 micromol/L. Intravenous sodium benzoate and sodium phenylacetate are given. How do…
- Amino acid metabolism: cystinosis · ApplicationA 14-month-old child has failure to thrive, polyuria, rickets and photophobia. Slit lamp examination shows corneal crystals, and white cells contain a high cystine cont…
- Amino acid metabolism: isovaleric acidaemia · ApplicationA 6-day-old infant develops vomiting, lethargy and metabolic acidosis after protein feeds. Nursing staff note a smell like sweaty feet. Which enzyme in the leucine path…
- Amino acid metabolism: homocystinuria · Multi-stepA 14-year-old tall boy with long limbs and intellectual impairment presents with a popliteal deep vein thrombosis. Slit-lamp examination shows downward lens dislocation…
- Amino acid metabolism: tryptophan in carcinoid syndrome · ApplicationA 55-year-old man with metastatic midgut carcinoid has flushing, diarrhoea and wheeze. His 24-hour urinary 5-HIAA is raised. Over months he also develops a scaly pigmen…
- Amino acid metabolism: hepatic encephalopathy · ApplicationA 52-year-old man with alcoholic cirrhosis becomes drowsy with asterixis after a gastrointestinal bleed. His plasma ammonia is raised. Which process in the brain contri…
- Amino acid metabolism: gamma-glutamyl cycle and 5-oxoproline · Multi-stepA malnourished 60-year-old woman on regular paracetamol for chronic pain is admitted with sepsis and a high anion gap metabolic acidosis. Lactate, ketones, osmolal gap…
- Amino acid metabolism: tetrahydrobiopterin deficiency · Multi-stepA 4-month-old has a newborn screen phenylalanine of 20 mg/dL. Despite strict dietary phenylalanine restriction, which normalised plasma phenylalanine, he develops hypot…
- Amino acid metabolism: ammonia management · ApplicationA man with cirrhosis has asterixis and confusion with a high arterial ammonia. He is started on oral lactulose. Which mechanism explains its benefit?
- Amino acid metabolism: branched-chain amino acids · ApplicationAfter a protein-rich meal, plasma levels of branched-chain amino acids rise less than other amino acids because the liver largely spares them. Which tissue mainly takes…
- Amino acid metabolism · ApplicationGlycine is a precursor of several biomolecules. Which of the following is NOT derived from glycine?
- Amino acid metabolism · ApplicationCarcinoid tumour cells divert large amounts of tryptophan into serotonin synthesis. Which enzyme catalyses the rate-limiting step of this pathway?
- Amino acid metabolism: phenylalanine hydroxylase · ApplicationIn an inborn error, a non-essential aromatic amino acid can no longer be made from the essential one that accumulates, so the non-essential one becomes conditionally es…
- Amino acid metabolism: phenylalanine hydroxylase · Multi-stepA newborn has a persistently raised blood level of an aromatic amino acid on screening. The urinary pterin profile is normal, and the level falls substantially after a…
- Amino acid metabolism: phenylalanine hydroxylase · Multi-stepA woman with an inherited disorder of aromatic amino acid metabolism stops her diet in pregnancy. Her infant, who does not carry the disorder, has microcephaly, congeni…
- Amino acid metabolism: phenylalanine hydroxylase · Multi-stepA child with fair skin and light hair has eczema and developmental delay, though both parents have brown hair. Melanocyte tyrosinase is structurally normal, but an accu…
- Amino acid metabolism: renal ammoniagenesis · ApplicationIn chronic metabolic acidosis the kidney excretes more ammonium in the urine. Which substrate and enzyme in the proximal tubular cell supply most of this ammonia?
- Amino acid metabolism: glutamate dehydrogenase · ApplicationWhich mitochondrial enzyme reversibly converts glutamate to alpha-ketoglutarate and ammonia using NAD+ or NADP+, and is allosterically activated by ADP?
- Amino acid metabolism: PAPS as sulfate donor · ApplicationThe sulfation of glycosaminoglycans, steroids and xenobiotics uses an activated form of sulfate. What is this universal sulfate donor?
- Amino acid metabolism: valproate and hyperammonaemia · Multi-stepA child on sodium valproate for epilepsy becomes lethargic and vomits. Liver enzymes are normal but ammonia is raised, and carbamoyl phosphate synthetase I activity is…
- Amino acid metabolism: urea cycle fumarate release · Multi-stepIn the urea cycle, cleavage of the intermediate formed from citrulline and aspartate releases arginine and a four-carbon compound. That compound is the metabolic link b…
- Amino acid metabolism: argininosuccinic aciduria · Multi-stepA 6-month-old girl has episodes of vomiting and lethargy after protein-rich feeds, with ammonia 400 micromol/L. Her hair is dry and breaks easily, and microscopy shows…
- Amino acid metabolism: citrullinaemia type I · ApplicationA 4-day-old neonate becomes lethargic and starts to hyperventilate with plasma ammonia of 1100 micromol/L. Amino acid analysis shows plasma citrulline many times above…
- Amino acid metabolism: HHH syndrome · Multi-stepA 5-year-old boy has episodic vomiting and confusion after protein-rich meals, with progressive spastic paraparesis. Plasma ammonia is raised during episodes, and urine…
- Amino acid metabolism: tyrosinaemia type II · ApplicationA 4-year-old boy has painful, photophobic eye lesions with pseudodendritic corneal erosions, painful thickening of the palms and soles, and mild intellectual disability…
- Amino acid metabolism: transient neonatal tyrosinaemia · ApplicationA premature infant fed a high-protein formula has mildly raised plasma tyrosine and phenylalanine with a normal urinary succinylacetone. Levels fall with protein restri…
- Amino acid metabolism: adrenal medulla epinephrine synthesis · ApplicationThe adrenal medulla secretes mainly epinephrine, whereas sympathetic nerve endings release norepinephrine. The medullary enzyme that makes epinephrine is induced by the…
- Amino acid metabolism: glutaric aciduria type I · Multi-stepA 10-month-old with an unusually large head circumference develops sudden dystonia and loss of motor milestones after a febrile gastroenteritis. MRI shows bilateral str…
- Amino acid metabolism: tryptophan load and vitamin B6 · ApplicationAfter an oral tryptophan load, a patient on long-term isoniazid excretes large amounts of xanthurenic acid in urine. Deficiency of which vitamin is suggested by this te…
- Amino acid metabolism: polyamine synthesis · ApplicationA patient with late-stage African trypanosomiasis is treated with eflornithine, a suicide inhibitor of the enzyme that decarboxylates an amino acid to make putrescine,…
- Amino acid metabolism: remethylation defect MTHFR · Multi-stepA 3-year-old with developmental delay and seizures has raised plasma and urinary homocysteine with low plasma methionine. There is no marfanoid habitus or lens dislocat…
- Amino acid metabolism: betaine in homocystinuria · ApplicationA child with B6-nonresponsive homocystinuria is given betaine in addition to a methionine-restricted diet. How does betaine lower plasma homocysteine?
- Amino acid metabolism: cysteine in cystathionine synthase deficiency · ApplicationA boy with classic homocystinuria is placed on a methionine-restricted diet. Which additional amino acid must be supplied because the metabolic block prevents its synth…
- Amino acid metabolism: maternal phenylketonuria · ApplicationA woman with classic phenylketonuria stopped her low-phenylalanine diet in adolescence. Her newborn, who has no phenylalanine hydroxylase deficiency, has microcephaly,…
- Amino acid metabolism: levodopa with carbidopa · ApplicationA patient with Parkinson disease receives levodopa combined with carbidopa. Carbidopa does not cross the blood-brain barrier. What is the biochemical purpose of adding…
- Amino acid metabolism: catecholamine degradation · ApplicationIn a child with suspected neuroblastoma, urinary vanillylmandelic acid is measured. This end product arises from catecholamines through the sequential action of which t…
- Amino acid metabolism: lysinuric protein intolerance · Multi-stepA 3-year-old avoids protein-rich food and has growth failure, hepatosplenomegaly and hyperammonaemia after protein meals. Urine shows high excretion of lysine, arginine…
- Amino acid metabolism: acid-base pattern of urea cycle defects · Multi-stepTwo neonates present on day 3 with poor feeding, lethargy and plasma ammonia above 600 micromol/L. Baby A has respiratory alkalosis with a normal anion gap and no urina…
- Amino acid metabolism: serine hydroxymethyltransferase · ApplicationA pyridoxal phosphate-dependent enzyme converts serine to glycine and transfers the removed carbon to tetrahydrofolate, forming N5,N10-methylene tetrahydrofolate. Which…
- Amino acid metabolism: ornithine aminotransferase deficiency · Multi-stepA 22-year-old has night blindness and progressively constricted visual fields. Fundoscopy shows sharply demarcated, scalloped areas of chorioretinal atrophy in the peri…
- Amino acid metabolism: biotinidase deficiency · Multi-stepA previously well 4-month-old develops seizures, hypotonia, scaly erythematous rash around the eyes and mouth, and patchy hair loss. Urine shows 3-hydroxyisovaleric aci…
- Amino acid metabolism: energy cost of urea synthesis · ApplicationSynthesis of one molecule of urea in the liver consumes ATP at two steps: carbamoyl phosphate formation and argininosuccinate formation. In terms of high-energy phospha…
- Amino acid metabolism: hyperinsulinism-hyperammonaemia syndrome · Multi-stepA 9-month-old has recurrent hypoglycaemia after protein-rich meals and fasting, with inappropriately high insulin and persistent mild hyperammonaemia of about 2 to 3 ti…
- Amino acid metabolism: propionyl-CoA precursor amino acids · ApplicationPropionyl-CoA is converted via methylmalonyl-CoA to succinyl-CoA. Which set of amino acids is catabolised partly through this route?
- Amino acid metabolism: cystinuria treatment · ApplicationA man with recurrent cystine stones continues to form them despite high fluid intake and urinary alkalinisation. A thiol drug that forms a more soluble mixed disulfide…
- Amino acid metabolism: tyrosine catabolic products · ApplicationTyrosine is degraded by transamination, oxidation and ring cleavage. The terminal products of this pathway enter intermediary metabolism, making tyrosine both glucogeni…
- Amino acid metabolism: isolated methylmalonic acidaemia · Multi-stepA 5-day-old neonate is vomiting and lethargic with tachypnoea, a high anion gap metabolic acidosis, ketonuria and hyperammonaemia. Urine organic acids show grossly rais…
- Amino acid metabolism: asparagine depletion therapy · ApplicationA child with acute lymphoblastic leukaemia is treated with L-asparaginase. What explains the selective toxicity of this enzyme to the leukaemic lymphoblasts?
- Amino acid metabolism: Reye syndrome · ApplicationA 7-year-old given aspirin during influenza develops vomiting, confusion, hypoglycaemia and a markedly raised plasma ammonia. Biopsy shows microvesicular fatty change i…
- Amino acid metabolism: carglumic acid · Multi-stepA neonate has hyperammonaemia with low plasma citrulline and low urinary orotic acid. CPS I is structurally normal, but the enzyme that forms its obligatory allosteric…
- Amino acid metabolism: glutamate dehydrogenase regulation · ApplicationGlutamate dehydrogenase carries out the main oxidative deamination in liver mitochondria. Which nucleotides inhibit it allosterically when the cell's energy charge is h…
- Amino acid metabolism: tyramine and monoamine oxidase inhibitors · ApplicationA depressed patient on phenelzine eats aged cheese and develops a throbbing headache and a hypertensive crisis. Which amine, formed by decarboxylation of an aromatic am…
- Amino acid metabolism: nitisinone in alkaptonuria · Multi-stepA man with alkaptonuria is given nitisinone, which lowers his urinary homogentisic acid. What is its site of action?
- Amino acid metabolism: nitric oxide synthase cofactors · ApplicationNitric oxide synthase oxidises arginine to citrulline and nitric oxide. Which set of cofactors does it require?
- Amino acid metabolism: homocysteine with methylmalonate · Multi-stepTwo patients have macrocytic anaemia with raised plasma homocysteine. Methylmalonic acid is raised in the first patient and normal in the second. What is the best inter…
- Amino acid metabolism: dopamine beta-hydroxylase and copper · ApplicationMenkes disease causes low plasma noradrenaline with a raised dopamine to noradrenaline ratio. Which trace element needed by dopamine beta-hydroxylase explains this?
- Amino acid metabolism: mixed glucogenic and ketogenic · ApplicationWhich one of these amino acids gives rise to both glucogenic and ketogenic products during catabolism?
- Amino acid metabolism: serine and threonine deamination · ApplicationMost amino acids are deaminated by transamination followed by oxidative deamination of glutamate. Which pair is deaminated directly and non-oxidatively by pyridoxal pho…
- Amino acid metabolism: isoniazid seizures and GABA synthesis · ApplicationA patient who swallowed a large quantity of isoniazid presents with refractory seizures. Which metabolic defect explains the fits, and what corrects it?
- Amino acid metabolism · ApplicationWhat is the principal nitrogenous waste product formed by the urea cycle?
- Amino acid metabolism · ApplicationWhich amino acid is a precursor for serotonin?
- Amino acid metabolism · ApplicationWhat cofactor is important for transamination reactions?
- Amino acid metabolism · ApplicationWhat amino acid is the precursor of catecholamines?
- Amino acid metabolism · ApplicationWhat amino acid is a precursor of nitric oxide?
- Amino acid metabolism · ApplicationWhere is ammonia converted to urea?
- Amino acid metabolism · ApplicationWhat amino acid is the precursor of histamine?
- Amino acid metabolism · ApplicationWhat amino acid is a precursor for melanin synthesis?
- Amino acid metabolism · ApplicationWhat is the major transport form of ammonia from muscle to liver?
- Amino acid metabolism · ApplicationWhich amino acid is an essential dietary amino acid in adults?
- Amino acid metabolism: maple syrup urine disease · ApplicationA neonate has poor feeding, dystonia and urine with a sweet odour. Defective oxidative decarboxylation of which amino acids is expected?
- Amino acid metabolism: phenylketonuria · ApplicationA child with phenylketonuria requires supplementation with which amino acid because it becomes essential?
Clinical biochemistry81
- Clinical biochemistry: glycated haemoglobin · ApplicationA man with type 2 diabetes and chronic haemolytic anaemia has an HbA1c of 5.2% while his home glucose readings are consistently above 250 mg/dL. What is the most likely…
- Clinical biochemistry: cardiac markers · ApplicationA 60-year-old man who had an acute myocardial infarction 3 days ago has fresh chest pain. Serum troponin I is still raised. Which marker best helps to decide whether re…
- Clinical biochemistry: anion gap · Multi-stepA 55-year-old man in septic shock has serum sodium 138 mmol/L, chloride 96 mmol/L and bicarbonate 10 mmol/L, with a pH of 7.18. What is the anion gap and what does it i…
- Clinical biochemistry: osmolal gap · Multi-stepA 30-year-old man is drowsy with visual blurring and metabolic acidosis. Measured serum osmolality is 330 mOsm/kg. Sodium is 140 mmol/L, glucose 90 mg/dL and blood urea…
- Clinical biochemistry: corrected calcium · Multi-stepA malnourished patient with nephrotic syndrome has a total serum calcium of 7.2 mg/dL and albumin of 2.0 g/dL. Using the standard correction, what is the albumin-correc…
- Clinical biochemistry: hypercalcaemia · ApplicationA 62-year-old smoker with a squamous cell lung carcinoma has confusion, polyuria and serum calcium 13.4 mg/dL. Serum intact parathyroid hormone is suppressed and phosph…
- Clinical biochemistry: thyroid function tests · ApplicationA 38-year-old woman has fatigue and mild constipation. TSH is 12 mIU/L with normal free T4 and free T3 on two occasions. Which interpretation is correct?
- Clinical biochemistry: urine ketone testing · ApplicationA 16-year-old with type 1 diabetes arrives in severe acidosis. Capillary blood beta-hydroxybutyrate is 6 mmol/L, but the urine nitroprusside test shows only a trace of…
- Clinical biochemistry: liver enzymes · ApplicationA 45-year-old man with chronic heavy alcohol use has AST 180 U/L, ALT 70 U/L, a raised GGT and an MCV of 106 fL. What is the most likely cause of the aminotransferase p…
- Clinical biochemistry: creatinine clearance · Multi-stepA 24-hour urine collection has a volume of 1440 mL and urine creatinine of 90 mg/dL. Plasma creatinine is 1.5 mg/dL. What is the creatinine clearance?
- Clinical biochemistry: fractional excretion of sodium · Multi-stepA 65-year-old man with vomiting and poor intake has serum creatinine 2.0 mg/dL and sodium 140 mmol/L. Urine sodium is 10 mmol/L and urine creatinine 100 mg/dL. What is…
- Clinical biochemistry: jaundice work-up · ApplicationA 55-year-old man has progressive jaundice, itching, dark urine and pale stools. Which pattern of laboratory findings is expected?
- Clinical biochemistry: rhabdomyolysis · ApplicationA 24-year-old recruit collapses after a long forced march and passes tea-coloured urine. Urine dipstick is strongly positive for blood, but microscopy shows no red cell…
- Clinical biochemistry: antenatal screening · ApplicationA 36-year-old pregnant woman has a second trimester quadruple test. Which pattern raises the risk of Down syndrome?
- Clinical biochemistry: pseudohyperkalaemia · Multi-stepA 35-year-old woman attending for a routine check-up has a serum potassium of 6.9 mmol/L. She is asymptomatic, her ECG is normal, renal function is normal and she takes…
- Clinical biochemistry: pleural fluid analysis · ApplicationA 50-year-old man has a pleural effusion. Pleural fluid protein is 3.5 g/dL with serum protein 6.0 g/dL, and pleural fluid LDH is 280 U/L with serum LDH 400 U/L. How is…
- Clinical biochemistry: ascitic fluid analysis · ApplicationA 48-year-old man has new ascites. Serum albumin is 3.0 g/dL and ascitic fluid albumin is 1.4 g/dL. What is the serum-ascites albumin gradient and what does it indicate?
- Clinical biochemistry: hypoglycaemia work-up · Multi-stepA 28-year-old nurse has recurrent symptomatic hypoglycaemia. During an episode, glucose is 38 mg/dL with insulin markedly raised, C-peptide suppressed, beta-hydroxybuty…
- Clinical biochemistry: haemoglobin variants · ApplicationA 22-year-old woman has mild anaemia with haemoglobin 10.5 g/dL, MCV 62 fL, red cell count 5.6 million per microlitre and a normal serum ferritin. Which investigation i…
- Clinical biochemistry: colorimetry calculation · Multi-stepIn a colorimetric glucose assay, a 200 mg/dL standard gives an absorbance of 0.40 at the same path length. A patient sample gives an absorbance of 0.25. Assuming the Be…
- Clinical biochemistry: rhabdomyolysis · ApplicationA 28-year-old man is brought after prolonged immobilisation following a drug overdose. His urine is dark brown, the dipstick is strongly positive for blood, and microsc…
- Clinical biochemistry: corrected sodium in hyperglycaemia · Multi-stepA 65-year-old man with type 2 diabetes is drowsy and dehydrated. Serum sodium is 126 mmol/L and plasma glucose 600 mg/dL. Using the correction of 1.6 mmol/L of sodium f…
- Clinical biochemistry: alpha-1 antitrypsin deficiency · ApplicationA 3-month-old infant has prolonged cholestatic jaundice. Serum protein electrophoresis shows a markedly reduced alpha-1 band, and the father, a smoker, has early-onset…
- Clinical biochemistry: diagnosis of diabetes · ApplicationA 45-year-old asymptomatic man has, on the same blood sample, a fasting plasma glucose of 132 mg/dL and an HbA1c of 6.8%. How should this be interpreted?
- Clinical biochemistry: cystatin C · ApplicationA 24-year-old bodybuilder taking creatine supplements has serum creatinine of 1.5 mg/dL, but no proteinuria and a normal ultrasound. Which marker is likely to estimate…
- Clinical biochemistry: porphyrias · ApplicationA 45-year-old man with hepatitis C and heavy alcohol use has fragile blisters on the backs of his hands after sun exposure, with facial hypertrichosis. His urine fluore…
- Clinical biochemistry: hyperglycaemic emergencies · Multi-stepA 74-year-old man with type 2 diabetes is drowsy and dehydrated after a week of infection. Plasma glucose is 900 mg/dL, effective osmolality 340 mOsm/kg, pH 7.36 and bi…
- Clinical biochemistry: potassium disorders · ApplicationA man with chronic kidney disease has serum potassium 7.2 mmol/L and an ECG showing peaked T waves with a widened QRS. Which intervention should be given first to prote…
- Clinical biochemistry: catecholamine metabolism · ApplicationA 35-year-old woman has paroxysmal headache, sweating and palpitations with blood pressure of 210/120 mmHg. Plasma free metanephrines are raised. Which pair of enzymes…
- Clinical biochemistry: adrenal enzyme defects · Multi-stepA 3-year-old boy shows early pubic hair and a deepening voice, with blood pressure above the 99th centile and low serum potassium. Which pair of steroids accumulates?
- Clinical biochemistry: protein electrophoresis · ApplicationA child with nephrotic syndrome has serum protein electrophoresis performed. Which pattern is expected?
- Clinical biochemistry: xanthochromia in subarachnoid haemorrhage · ApplicationA man has a sudden severe headache and a normal CT scan of the head. Lumbar puncture 14 hours after onset gives CSF that is yellow after centrifugation. Which pigment f…
- Clinical biochemistry: oligoclonal bands · ApplicationA 29-year-old woman has episodes of optic neuritis and sensory loss disseminated in time and space. CSF electrophoresis shows IgG bands that are absent in the paired se…
- Clinical biochemistry: NT-proBNP with sacubitril · Multi-stepA man with chronic heart failure is switched from valsartan to sacubitril-valsartan. His BNP rises after the change though he feels better. Which biomarker is preferred…
- Clinical biochemistry: bone turnover markers · ApplicationA postmenopausal woman is monitored on a bisphosphonate. Which of the following is a marker of bone resorption rather than bone formation?
- Clinical biochemistry: EDTA contamination of a sample · Multi-stepA well outpatient's serum shows potassium 9.5 mmol/L, calcium 0.9 mmol/L and very low alkaline phosphatase, with a normal ECG. The sample was drawn after an EDTA tube.…
- Clinical biochemistry: chloride shift · ApplicationThe chloride content of red cells in venous blood is higher than in arterial blood. Which process explains this?
- Clinical biochemistry: faecal elastase · ApplicationA man with chronic alcohol use has weight loss and loose pale stools. Which stool test is a simple, non-invasive marker of exocrine pancreatic insufficiency and is not…
- Clinical biochemistry: hook effect in immunoassays · Multi-stepA woman with a large pituitary mass and headache has a serum prolactin reported as mildly raised. Her symptoms suggest a much higher level. The laboratory repeats the a…
- Clinical biochemistry: biotin interference · Multi-stepA woman taking high-dose biotin supplements for hair loss has a thyroid profile showing very low TSH with high free T4 and free T3, though she has no symptoms of thyrot…
- Clinical biochemistry: water deprivation test · ApplicationA man passes 8 litres of dilute urine daily. After water deprivation, urine osmolality stays at 150 mOsm/kg, and after desmopressin it rises to 600 mOsm/kg. What is the…
- Clinical biochemistry: primary hyperparathyroidism · ApplicationA 52-year-old woman has recurrent renal stones and constipation. Serum calcium is 11.4 mg/dL, phosphate is low and intact PTH is raised. Which additional finding is mos…
- Clinical biochemistry: hypoparathyroidism after thyroidectomy · ApplicationTwo days after total thyroidectomy, a woman has perioral tingling, and inflating a blood pressure cuff above systolic pressure induces carpopedal spasm. Which laborator…
- Clinical biochemistry: biochemistry of pyloric stenosis · ApplicationA 5-week-old firstborn boy has projectile non-bilious vomiting after every feed and a palpable olive-shaped epigastric mass. Which biochemical profile is expected?
- Clinical biochemistry: CSF in Guillain-Barre syndrome · ApplicationA 30-year-old man has ascending symmetric limb weakness and absent reflexes two weeks after an episode of diarrhoea. Which CSF finding is characteristic?
- Clinical biochemistry: dexamethasone suppression tests · Multi-stepA 38-year-old woman with central obesity, purple striae and hypertension fails to suppress serum cortisol after a low-dose dexamethasone test. ACTH is high-normal, and…
- Clinical biochemistry: Crigler-Najjar syndrome type I · Multi-stepA newborn is deeply jaundiced from day 2, with unconjugated bilirubin above 25 mg/dL, normal liver enzymes, no haemolysis and a negative Coombs test. Phototherapy helps…
- Clinical biochemistry: secretin test for gastrinoma · Multi-stepA 45-year-old man has recurrent duodenal ulcers and diarrhoea. Fasting gastrin is markedly raised with gastric pH 1.5. After intravenous secretin, serum gastrin rises s…
- Clinical biochemistry: coeliac serology with IgA deficiency · Multi-stepA 28-year-old woman with chronic diarrhoea and iron deficiency has a negative IgA anti-tissue transglutaminase result, but total serum IgA is markedly low. What is the…
- Clinical biochemistry: markers of intravascular haemolysis · ApplicationTwo hours after a mismatched transfusion, a patient has dark urine and jaundice. Which laboratory pattern supports intravascular haemolysis?
- Clinical biochemistry: mixed acid-base disorder in salicylate poisoning · Multi-stepA 20-year-old is brought after ingesting a large number of analgesic tablets and has tinnitus, fever and rapid deep breathing. ABG shows pH 7.46, PaCO2 22 mmHg and HCO3…
- Clinical biochemistry: pulse oximetry in carbon monoxide poisoning · ApplicationFour members of a family are drowsy with headache after sleeping in a closed room with a coal heater. A pulse oximeter reads 98% in each. Why is the reading misleadingl…
- Clinical biochemistry: Rotor syndrome · Multi-stepA 12-year-old has lifelong mild jaundice with mainly conjugated hyperbilirubinaemia and normal ALT and ALP. Liver biopsy shows normal histology without any pigment, and…
- Clinical biochemistry: hypophosphatasia · Multi-stepAn infant has poor bone mineralisation with rachitic changes, premature loss of deciduous teeth with intact roots, hypercalcaemia and an unusually low serum alkaline ph…
- Clinical biochemistry: delta ratio in mixed acid-base disorders · Multi-stepA man with diabetic ketoacidosis has also vomited repeatedly. Na is 140, Cl 90 and HCO3 18 mmol/L. Taking a normal anion gap as 12 and normal bicarbonate as 24, what is…
- Clinical biochemistry: prevalence and predictive values · ApplicationA screening test of fixed sensitivity and specificity is moved from a general clinic to a referral clinic where disease prevalence is much higher. What happens to its p…
- Clinical biochemistry: ionised calcium in hyperventilation · ApplicationA 22-year-old with a panic attack has rapid breathing, perioral tingling and carpopedal spasm. Serum total calcium is normal. What explains the tetany?
- Clinical biochemistry: CSF patterns in meningitis · ApplicationCSF from a febrile adult with neck stiffness shows 1,800 cells/mm3, mainly neutrophils, protein 260 mg/dL and glucose 18 mg/dL with a simultaneous blood glucose of 100…
- Clinical biochemistry: macroamylasaemia · Multi-stepA 40-year-old man without abdominal pain has persistently raised serum amylase, but serum lipase is normal and urinary amylase excretion is low. What is the likely expl…
- Clinical biochemistry: familial hypocalciuric hypercalcaemia · Multi-stepAn asymptomatic 35-year-old has mild hypercalcaemia since childhood, similar results in her father, normal to slightly raised PTH, and low urinary calcium excretion wit…
- Clinical biochemistry: central hypothyroidism · Multi-stepA woman who had pituitary surgery has fatigue and cold intolerance. Free T4 is low and TSH is 1.8 mIU/L (reference range 0.4 to 4.0). What does this pattern indicate?
- Clinical biochemistry: distal renal tubular acidosis · ApplicationA 25-year-old woman with Sjogren syndrome has a normal anion gap metabolic acidosis, hypokalaemia, nephrocalcinosis and a urine pH persistently above 5.5. What is the d…
- Clinical biochemistry: screening for primary aldosteronism · ApplicationA 40-year-old with resistant hypertension has persistent hypokalaemia and mild metabolic alkalosis. Which screening test best identifies primary aldosteronism?
- Clinical biochemistry: Gitelman syndrome · Multi-stepA 25-year-old has cramps and fatigue with normal blood pressure. Serum potassium is 2.8 mmol/L, magnesium is low, there is metabolic alkalosis, urinary calcium excretio…
- Clinical biochemistry: Liddle syndrome · Multi-stepA 20-year-old has early-onset hypertension, hypokalaemia and metabolic alkalosis with low renin and low aldosterone. Spironolactone does not correct the hypokalaemia bu…
- Clinical biochemistry: Bartter syndrome · ApplicationAn infant has polyuria, failure to thrive and normal blood pressure. Biochemistry shows hypokalaemia, metabolic alkalosis and hypercalciuria, and ultrasound shows nephr…
- Clinical biochemistry: Gilbert syndrome · ApplicationA 19-year-old has mild jaundice during fasting and intercurrent illness. Unconjugated bilirubin is 2.8 mg/dL, liver enzymes and blood count are normal, there is no haem…
- Clinical biochemistry: 72-hour fast and insulinoma · Multi-stepA 40-year-old has early-morning sweating and confusion relieved by glucose. During a supervised fast, glucose falls to 38 mg/dL with insulin, C-peptide and proinsulin a…
- Clinical biochemistry: D-lactic acidosis · Multi-stepA woman with short bowel after ileal resection has episodes of confusion, slurred speech and ataxia after carbohydrate-rich meals. She has a high anion gap acidosis, bu…
- Clinical biochemistry: alcoholic ketoacidosis · Multi-stepA chronic drinker who binged and then vomited and did not eat for 2 days has Kussmaul breathing, glucose 70 mg/dL, pH 7.20 and a high anion gap. The urine nitroprusside…
- Clinical biochemistry: compensation in chronic respiratory acidosis · ApplicationA man with long-standing COPD has stable chronic CO2 retention with PaCO2 of 70 mmHg. Which serum bicarbonate is best explained by full renal compensation of this chron…
- Clinical biochemistry: non-thyroidal illness · ApplicationA septic patient on a ventilator has TSH 0.6 mIU/L, low free T3, low-normal free T4 and a raised reverse T3. There is no history of thyroid disease. What is the best in…
- Clinical biochemistry: macroprolactin · Multi-stepA woman with oligomenorrhoea has serum prolactin 90 ng/mL, a normal pituitary MRI and no galactorrhoea. After precipitation with polyethylene glycol, the prolactin fall…
- Clinical biochemistry: conjugated bilirubin bound to albumin · ApplicationA patient's bile duct obstruction is relieved and conjugated bilirubin falls, but total bilirubin takes weeks to normalise. Which fraction, covalently bound to albumin,…
- Clinical biochemistry: effective plasma osmolality · ApplicationA diabetic in hyperosmolar crisis has sodium 140 mmol/L, glucose 540 mg/dL and urea 28 mg/dL. Using glucose divided by 18, what is the effective plasma osmolality?
- Clinical biochemistry: albumin and the anion gap · ApplicationA patient with cirrhosis and a serum albumin of 1.8 g/dL has lactic acidosis, but the calculated anion gap is only mildly raised. Why can the gap understate the acidosi…
- Clinical biochemistry: thyroxine-binding globulin in pregnancy · ApplicationA healthy pregnant woman at 20 weeks has no symptoms, a normal TSH and free T4, but total T4 is much higher than the non-pregnant range. What explains this?
- Clinical biochemistry: Paget disease of bone · ApplicationA 70-year-old has bone pain, an enlarging skull and deafness. Serum alkaline phosphatase is ten times normal, GGT is normal, and calcium and phosphate are normal. What…
- Clinical biochemistry: heterophilic antibody interference · Multi-stepA woman has a persistently positive serum beta-hCG of 40 IU/L with no pregnancy on ultrasound. Urine hCG is negative, and the serum result does not fall in a linear way…
- Clinical biochemistry: low anion gap and paraprotein · Multi-stepA 65-year-old with anaemia and back pain has a calculated anion gap of 2 mmol/L, a raised total protein, normal albumin and no history of drug use. What is the most lik…
- Clinical biochemistry: type 4 renal tubular acidosis · Multi-stepA 62-year-old with long-standing diabetes and mild chronic kidney disease has potassium 5.9 mmol/L, bicarbonate 18 mmol/L, a normal anion gap, urine pH below 5.5, and l…
Carbohydrate metabolism68
- Carbohydrate metabolism: pyruvate dehydrogenase · ApplicationA chronic alcoholic presents with confusion, ophthalmoplegia and lactic acidosis. Which enzyme complex needs the cofactor whose deficiency is responsible, besides alpha…
- Carbohydrate metabolism: fructose · ApplicationA 1-year-old develops vomiting, hypoglycaemia and jaundice soon after fruit juice and sucrose are introduced. Reducing substances are present in urine. Which enzyme is…
- Carbohydrate metabolism: Cori cycle · ApplicationDuring a sprint, muscle produces lactate that is later converted to glucose elsewhere. Which statement about this cycle is correct?
- Carbohydrate metabolism: glucagon · ApplicationDuring a prolonged fast, glucagon acts on the liver mainly by:
- Carbohydrate metabolism: galactose · ApplicationA 10-day-old breastfed neonate has jaundice, vomiting, poor feeding and hepatomegaly. Blood culture grows Escherichia coli. Urine is positive for reducing substances wi…
- Carbohydrate metabolism: essential fructosuria · ApplicationA healthy 6-year-old child has a routine urine test positive for reducing substances but negative on a glucose oxidase strip, especially after fruit juice. There is no…
- Carbohydrate metabolism: fructose-2,6-bisphosphate · Multi-stepOne hour after a carbohydrate-rich meal, the insulin to glucagon ratio is high. What happens in hepatocytes?
- Carbohydrate metabolism: glucokinase · Multi-stepA lean 17-year-old girl has asymptomatic fasting glucose values of 118 to 126 mg/dL on repeated testing, HbA1c 6.4% and negative islet autoantibodies. Her mother and ma…
- Carbohydrate metabolism: uronic acid pathway · ApplicationA healthy 35-year-old man of Ashkenazi Jewish descent has repeatedly positive urinary Benedict tests with a negative glucose oxidase result. His blood glucose is normal…
- Carbohydrate metabolism: polyol pathway · ApplicationIn a patient with poorly controlled diabetes, which mechanism best explains osmotic swelling of lens fibres leading to cataract?
- Carbohydrate metabolism: PDH complex deficiency · ApplicationA 6-month-old boy has hypotonia, developmental delay and persistent lactic acidosis. Pyruvate is raised in proportion to lactate. Enzyme assay shows deficiency of the E…
- Carbohydrate metabolism: galactosemia · ApplicationA 10-day-old breastfed neonate has jaundice, vomiting and poor feeding, and develops Escherichia coli sepsis. Slit-lamp examination shows bilateral oil-drop cataracts.…
- Carbohydrate metabolism: glucokinase and MODY · Multi-stepA 22-year-old woman has a fasting plasma glucose of 118 mg/dL on three occasions, HbA1c 6.4% and a 2-hour OGTT glucose of 150 mg/dL. She is lean and asymptomatic, her f…
- Carbohydrate metabolism: metformin and lactate · ApplicationA 68-year-old man with type 2 diabetes and an estimated GFR of 18 mL/min, who is still taking metformin, presents with vomiting, hyperventilation and a pH of 7.12. Lact…
- Carbohydrate metabolism: gluconeogenesis regulation · ApplicationDuring prolonged fasting, hepatic beta-oxidation raises mitochondrial acetyl-CoA. Which enzyme is directly activated by acetyl-CoA to favour conversion of pyruvate to o…
- Carbohydrate metabolism: glycaemic index · Multi-stepA dietician tests a food containing 50 g of available carbohydrate. The incremental 2-hour area under the blood glucose curve is 35 units. The same person, eating 50 g…
- Carbohydrate metabolism: Cori cycle · ApplicationDuring a sprint, lactate leaves muscle, is converted to glucose in the liver and returns to muscle. What is the net ATP cost of this cycle?
- Carbohydrate metabolism: GLUT1 deficiency syndrome · Multi-stepAn infant has seizures from the second month, acquired microcephaly and developmental delay. Blood glucose is normal, but CSF glucose is low with a normal CSF lactate.…
- Carbohydrate metabolism: GLUT2 defect in Fanconi-Bickel syndrome · Multi-stepAn infant has failure to thrive, hepatomegaly, rickets and proximal renal tubular dysfunction with glycosuria, phosphaturia and aminoaciduria. There is fasting hypoglyc…
- Carbohydrate metabolism: glycogenin primes glycogen synthesis · ApplicationGlycogen synthase can extend an existing chain but cannot start a new one. Which protein provides the starting primer for a new glycogen molecule?
- Carbohydrate metabolism: insulin signalling to GLUT4 · ApplicationAfter insulin binds its receptor, which downstream sequence mainly leads to GLUT4 translocation to the plasma membrane in muscle and adipocytes?
- Carbohydrate metabolism: galactokinase deficiency · ApplicationA 3-month-old breastfed infant has bilateral lens opacities. There is no jaundice, hepatomegaly, vomiting or sepsis, and urine is positive for a reducing sugar. Galacto…
- Carbohydrate metabolism: glycerol kinase deficiency · Multi-stepA boy with Duchenne muscular dystrophy and adrenal hypoplasia is found to have a markedly raised triglyceride level on a routine lipid profile, yet his plasma is clear…
- Carbohydrate metabolism: trapping of fluorodeoxyglucose · ApplicationFluorodeoxyglucose labelled with fluorine-18 is injected for a PET scan and accumulates in metabolically active tumour cells. Why does it remain trapped inside the cell?
- Carbohydrate metabolism: alpha-glucosidase inhibitors · ApplicationA man with type 2 diabetes is started on a tablet that lowers the rise in blood glucose after starchy meals but causes flatulence and bloating. Which enzymes does the d…
- Carbohydrate metabolism: SGLT2 inhibition · ApplicationA patient with type 2 diabetes is started on a new tablet. Soon afterwards he has glucose in his urine despite only modestly raised plasma glucose, and develops genital…
- Carbohydrate metabolism: 2,3-bisphosphoglycerate synthesis · ApplicationRed cells generate 2,3-bisphosphoglycerate by diverting an intermediate of glycolysis, bypassing the first ATP-generating step. Which enzyme catalyses the diversion?
- Carbohydrate metabolism: dichloroacetate and lactic acidosis · ApplicationDichloroacetate lowers lactate in some cases of congenital lactic acidosis by increasing flux through pyruvate dehydrogenase. Which enzyme does it inhibit?
- Carbohydrate metabolism: lactose synthase · ApplicationIn the lactating mammary gland, galactosyltransferase normally transfers galactose to proteins. A regulatory protein changes its specificity so that glucose becomes the…
- Carbohydrate metabolism: vitamin B6 in glycogen phosphorylase · Multi-stepMost of the body's pyridoxal phosphate is found in skeletal muscle. The vitamin is mainly bound to which enzyme?
- Carbohydrate metabolism: fructose and lipogenesis · Multi-stepA 30-year-old man consuming large amounts of sugar-sweetened beverages develops raised hepatic triglyceride and fatty liver. Which feature of hepatic fructose metabolis…
- Carbohydrate metabolism: ATP yield from glycogen · ApplicationDuring intense exercise, a muscle fibre degrades glycogen to lactate under anaerobic conditions. What is the net ATP gain per glucose unit taken from glycogen?
- Carbohydrate metabolism: familial renal glycosuria · ApplicationA healthy 25-year-old has persistent glucose in the urine on routine testing. Fasting and post-prandial plasma glucose, HbA1c and an oral glucose tolerance test are all…
- Carbohydrate metabolism: L-gulonolactone oxidase and ascorbate · ApplicationMost mammals make ascorbic acid from glucose through the uronic acid pathway, but humans and guinea pigs cannot and need it in the diet. Which enzyme is non-functional…
- Carbohydrate metabolism: glycogen storage disease type Ib · Multi-stepA 2-year-old with hepatomegaly, fasting hypoglycaemia, lactic acidosis and hyperuricaemia also has recurrent bacterial infections, oral ulcers and neutropenia. Glucose-…
- Carbohydrate metabolism: AMP and muscle glycogen phosphorylase b · ApplicationIn a sprinting muscle, the less phosphorylated, 'b' form of glycogen phosphorylase can still be driven to break down glycogen. Which allosteric effector activates it?
- Carbohydrate metabolism: glucose sensing by the pancreatic beta cell · Multi-stepAfter a meal, glucose enters beta cells and is phosphorylated. Insulin secretion then follows a sequence of events. Which step comes directly before the opening of volt…
- Carbohydrate metabolism · ApplicationWhat is the principal storage form of glucose in liver and muscle?
- Carbohydrate metabolism · ApplicationWhat is the end product of anaerobic glycolysis in muscle?
- Carbohydrate metabolism · ApplicationWhich organ is a major site of gluconeogenesis during fasting?
- Carbohydrate metabolism · ApplicationWhich hormone promotes glycogen breakdown in the liver during fasting?
- Carbohydrate metabolism · ApplicationWhat enzyme is deficient in classic galactosemia?
- Carbohydrate metabolism · ApplicationWhat enzyme phosphorylates glucose in most tissues at the start of glycolysis?
- Carbohydrate metabolism · ApplicationWhat molecule is the immediate product of glycogen breakdown by glycogen phosphorylase?
- Carbohydrate metabolism · ApplicationWhat is the rate-limiting enzyme of glycolysis?
- Carbohydrate metabolism · ApplicationWhat pathway generates NADPH and ribose-5-phosphate?
- Carbohydrate metabolism · ApplicationWhat enzyme deficiency causes hereditary fructose intolerance?
- Carbohydrate metabolism · ApplicationWhat enzyme converts glucose-6-phosphate to fructose-6-phosphate in glycolysis?
- Carbohydrate metabolism · ApplicationWhat is the committed rate-limiting enzyme of glycolysis?
- Carbohydrate metabolism · ApplicationWhat enzyme releases free glucose from hepatic glucose-6-phosphate?
- Carbohydrate metabolism · ApplicationWhat cofactor is required by pyruvate dehydrogenase?
- Carbohydrate metabolism · ApplicationWhat is the principal storage carbohydrate in animals?
- Carbohydrate metabolism · ApplicationWhich enzyme is the principal rate-limiting enzyme of glycolysis in most tissues?
- Carbohydrate metabolism · ApplicationWhich cofactor is required by the pyruvate dehydrogenase complex and is derived from vitamin B1?
- Carbohydrate metabolism · ApplicationDuring fasting, which hormone most directly stimulates hepatic glycogen breakdown?
- Carbohydrate metabolism · ApplicationWhich organ normally contributes most to gluconeogenesis during an overnight fast?
- Carbohydrate metabolism · ApplicationWhat is the main metabolic purpose of glycolysis?
- Carbohydrate metabolism · ApplicationWhich organ is chiefly responsible for maintaining blood glucose during an overnight fast?
- Carbohydrate metabolism · ApplicationDuring prolonged fasting, which hepatic pathway produces glucose from lactate and amino-acid carbon skeletons?
- Carbohydrate metabolism: fructose · Multi-stepAn infant develops vomiting, jaundice and hypoglycaemia after fruit juice is introduced. Accumulation of fructose-1-phosphate points to deficiency of which enzyme?
- Carbohydrate metabolism: gluconeogenesis · ApplicationWhich enzyme bypasses the irreversible phosphofructokinase-1 step during gluconeogenesis?
- Carbohydrate metabolism · ApplicationWhich tissue cannot use fatty acids directly for fuel during fasting?
- Carbohydrate metabolism · ApplicationWhich enzyme releases free glucose from glucose-6-phosphate in the fasting liver?
- Carbohydrate metabolism · ApplicationWhich pathway supplies NADPH for reductive biosynthesis?
- Carbohydrate metabolism · ApplicationWhy can G6PD deficiency cause haemolysis after oxidant stress?
- Carbohydrate metabolism: glycolysis · ApplicationWhich glycolytic enzyme is the principal rate-limiting regulatory enzyme in most tissues?
- Carbohydrate metabolism: fructose · ApplicationA child develops vomiting, hypoglycemia, and jaundice after introduction of fruit juice. Which enzyme deficiency is most likely?
- Carbohydrate metabolism: galactose · ApplicationAn infant has jaundice, hepatomegaly, cataracts, and poor feeding after milk feeds. Which enzyme deficiency is most likely?
Lipid metabolism62
- Lipid metabolism: fatty acid oxidation · ApplicationA toddler becomes lethargic and hypoglycaemic after a prolonged fast, with a low urinary ketone level and raised urinary dicarboxylic acids. What is the most likely dia…
- Lipid metabolism: malonyl-CoA regulation of oxidation · Multi-stepAfter a carbohydrate-rich meal, hepatic fatty acid oxidation is suppressed even though fatty acids still reach the liver. Which sequence best explains this?
- Lipid metabolism: fatty liver · ApplicationA malnourished man on long-term parenteral nutrition free of choline develops hepatic steatosis with raised transaminases. Which mechanism best explains the fat accumul…
- Lipid metabolism: fatty acid oxidation defects · ApplicationAn 18-month-old becomes lethargic after a day of gastroenteritis with poor intake. Glucose is 28 mg/dL, urine ketones are absent and there is mild hyperammonaemia. What…
- Lipid metabolism · ApplicationA rare loss-of-function mutation in a plasma protein produces very high HDL cholesterol, because exchange of core lipids between HDL and apoB-containing lipoproteins is…
- Lipid metabolism · ApplicationA fasting plasma sample looks milky. After standing overnight, a cream layer forms on top, and agarose gel electrophoresis shows a dense band at the origin. Which lipop…
- Lipid metabolism: colipase and pancreatic lipase · ApplicationA man with chronic pancreatitis has pale, bulky, foul-smelling stools. In the intestinal lumen, pancreatic lipase needs which protein to bind the emulsified fat droplet…
- Lipid metabolism: D-xylose absorption test · Multi-stepA patient with steatorrhoea and normal renal function drinks 25 g of D-xylose, and urinary excretion over five hours is markedly reduced. Which cause of steatorrhoea is…
- Lipid metabolism: 5-lipoxygenase and leukotrienes · ApplicationA drug used in asthma reduces synthesis of the leukotrienes LTC4, LTD4 and LTE4 by inhibiting an enzyme of arachidonic acid metabolism. Which enzyme does it inhibit?
- Lipid metabolism: Farber disease · Multi-stepAn infant has a hoarse cry, painful swollen joints, subcutaneous nodules and progressive neurological decline. Tissues show lysosomal accumulation of ceramide. Which en…
- Lipid metabolism: sitosterolaemia · Multi-stepA child has tendon xanthomas and early atherosclerosis with normal or only mildly raised plasma cholesterol. Plant sterols such as sitosterol are markedly elevated and…
- Lipid metabolism: phosphatidylserine externalisation in apoptosis · ApplicationAnnexin V staining is used to detect early apoptotic cells. Which membrane phospholipid, normally confined to the inner leaflet, is exposed on the cell surface and boun…
- Lipid metabolism: conjugation of bile acids · ApplicationPrimary bile acids are conjugated in the liver before secretion. With which amino acids are they conjugated, and why does this help?
- Lipid metabolism: citrate shuttle for fatty acid synthesis · ApplicationIn a well-fed liver cell, acetyl-CoA formed from pyruvate inside mitochondria is needed in the cytosol for fatty acid synthesis. How does it reach the cytosol?
- Lipid metabolism: primary carnitine deficiency · Multi-stepA 2-year-old has dilated cardiomyopathy, muscle weakness and fasting hypoketotic hypoglycaemia. Plasma free carnitine is very low with excessive urinary carnitine loss,…
- Lipid metabolism: oxidation of unsaturated fatty acids · Multi-stepDuring beta-oxidation of oleic acid, the cis double bond lies at an odd-numbered carbon and the usual hydratase step cannot proceed. Which additional enzyme repositions…
- Lipid metabolism: glycerol-3-phosphate in adipose tissue · Multi-stepAdipocytes lack glycerol kinase. In the fed state, from where does the glycerol-3-phosphate needed to esterify fatty acids come?
- Lipid metabolism: cholesterol gallstones · ApplicationA 42-year-old obese woman has cholesterol gallstones. Which abnormality of bile composition favours cholesterol crystal formation?
- Lipid metabolism: glucocorticoids and phospholipase A2 · ApplicationGlucocorticoids reduce production of both prostaglandins and leukotrienes by inducing annexin-1 (lipocortin). Which enzyme does this protein inhibit?
- Lipid metabolism: alcoholic fatty liver · Multi-stepA chronic alcohol user has an enlarged, fatty liver on ultrasound. Which metabolic change from ethanol oxidation contributes most directly to triglyceride accumulation?
- Lipid metabolism: rate-limiting step of bile acid synthesis · ApplicationWhich enzyme catalyses the rate-limiting step in the conversion of cholesterol to primary bile acids and is down-regulated when bile acids return through the enterohepa…
- Lipid metabolism: cholestasis and fat malabsorption · ApplicationA 55-year-old man with a carcinoma obstructing the common bile duct has pale, greasy stools. Which defect in lipid digestion explains the steatorrhoea?
- Lipid metabolism: foam cell formation · Multi-stepIn early atherosclerosis, subendothelial macrophages become lipid-laden foam cells even though cellular cholesterol content is high. Which uptake pathway explains the c…
- Lipid metabolism: ACAT and intracellular cholesterol esterification · ApplicationWhen free cholesterol builds up inside a cell, an endoplasmic reticulum enzyme esterifies it with a fatty acyl group for storage in droplets. Which enzyme is this?
- Lipid metabolism: fatty liver in kwashiorkor · ApplicationA 2-year-old on a low-protein, starchy diet has oedema and an enlarged, fatty liver. Which mechanism best explains the hepatic fat accumulation?
- Lipid metabolism: lipoprotein lipase in fasting · Multi-stepIn the fasting state, plasma triglyceride-rich lipoproteins are directed toward heart and skeletal muscle rather than adipose tissue. Which change in lipoprotein lipase…
- Lipid metabolism: fibrates and PPAR-alpha · ApplicationA man with triglycerides of 800 mg/dL and low HDL cholesterol is started on fenofibrate. Which receptor does the drug activate to lower triglycerides?
- Lipid metabolism: hepatic lipase · ApplicationAn endothelium-bound lipase on the sinusoidal surface of hepatocytes hydrolyses triglycerides and phospholipids in IDL and in HDL2. Which enzyme is this?
- Lipid metabolism: fetal LCHAD deficiency and acute fatty liver of pregnancy · Multi-stepA woman at 35 weeks of gestation has vomiting, jaundice, hypoglycaemia and coagulopathy from acute fatty liver of pregnancy. Her newborn later develops hypoketotic hypo…
- Lipid metabolism: salicylate and Reye syndrome · ApplicationA 7-year-old recovering from varicella was given aspirin and now has persistent vomiting, confusion, hypoglycaemia and hyperammonaemia. Liver biopsy shows microvesicula…
- Lipid metabolism: re-esterification of dietary fat in enterocytes · ApplicationAfter absorption of monoacylglycerol and free fatty acids, enterocytes must rebuild triglycerides before they are packed into chylomicrons. Which pathway mainly carries…
- Lipid metabolism: platelet-activating factor · ApplicationA mediator released by activated neutrophils and macrophages is an ether-linked phospholipid with an alkyl chain at position 1 and an acetyl group at position 2 of glyc…
- Lipid metabolism: prostaglandin E1 and the ductus arteriosus · ApplicationA newborn with critical pulmonary atresia is cyanosed at 2 days of age as the ductus arteriosus begins to close. An infusion is started to keep the vessel open. Which e…
- Lipid metabolism: ursodeoxycholic acid · ApplicationA frail 70-year-old woman with small radiolucent cholesterol gallstones and mild symptoms refuses surgery. Which bile acid is given orally to dissolve the stones?
- Lipid metabolism: bile acid diarrhoea after ileal resection · Multi-stepAfter resection of 60 cm of terminal ileum for Crohn disease, a man has watery diarrhoea but no steatorrhoea. The diarrhoea improves with cholestyramine. What explains…
- Lipid metabolism: Niemann-Pick disease type C · Multi-stepA 7-year-old with earlier neonatal jaundice and hepatosplenomegaly now has ataxia, dystonia, dysarthria and loss of voluntary vertical eye movement. Filipin staining of…
- Lipid metabolism · ApplicationWhat is the main storage form of fat in adipose tissue?
- Lipid metabolism · ApplicationWhich lipoprotein carries dietary triglycerides from intestine?
- Lipid metabolism · ApplicationWhich enzyme is inhibited by statin drugs?
- Lipid metabolism · ApplicationWhat is the major role of HDL in lipid transport?
- Lipid metabolism · ApplicationWhere does beta-oxidation of fatty acids occur primarily?
- Lipid metabolism · ApplicationWhat molecule transports long-chain fatty acids into mitochondria for beta-oxidation?
- Lipid metabolism · ApplicationWhat is the main ketone body produced during prolonged fasting?
- Lipid metabolism · ApplicationWhich lipoprotein primarily delivers cholesterol to peripheral tissues?
- Lipid metabolism · ApplicationWhat enzyme is responsible for rate-limiting fatty-acid synthesis?
- Lipid metabolism · ApplicationWhat enzyme hydrolyzes triglycerides in chylomicrons at capillary endothelium?
- Lipid metabolism · ApplicationWhat ketone body cannot be used as fuel by the liver?
- Lipid metabolism · ApplicationWhat lipoprotein primarily delivers endogenous triglycerides from liver?
- Lipid metabolism · ApplicationWhich molecule transports long-chain fatty acids into mitochondria for beta-oxidation?
- Lipid metabolism · ApplicationWhy can the liver produce ketone bodies but not use them as a major fuel source?
- Lipid metabolism · ApplicationWhich enzyme is inhibited by statins to lower cholesterol synthesis?
- Lipid metabolism · ApplicationWhich transport mechanism moves long-chain fatty acyl groups into mitochondria for beta-oxidation?
- Lipid metabolism · ApplicationWhat is the main role of lipoprotein lipase?
- Lipid metabolism · ApplicationWhich lipoprotein carries dietary triglycerides from the intestine?
- Lipid metabolism: carnitine shuttle · ApplicationLong-chain fatty acids require which molecule to enter the mitochondrial matrix for beta-oxidation?
- Lipid metabolism: ketone bodies · ApplicationWhy cannot hepatocytes use ketone bodies as a major fuel despite producing them during fasting?
- Lipid metabolism · ApplicationWhich hormone activates hormone-sensitive lipase in adipose tissue?
- Lipid metabolism · ApplicationWhat is the main source of ketone bodies during prolonged fasting?
- Lipid metabolism · ApplicationWhich lipoprotein participates in reverse cholesterol transport?
- Lipid metabolism: beta oxidation · ApplicationWhich finding is expected in medium-chain acyl-CoA dehydrogenase deficiency during fasting?
- Lipid metabolism: carnitine shuttle · ApplicationWhat is the main role of carnitine in fatty-acid metabolism?
- Lipid metabolism: ketone bodies · ApplicationWhich organ cannot use ketone bodies as a fuel because it lacks thiophorase?
Vitamins49
- Vitamins · ApplicationA patient with megaloblastic anaemia and mild neurological signs has raised serum methylmalonic acid. Which deficiency is most likely?
- Vitamins · ApplicationWernicke encephalopathy results from deficiency of which vitamin?
- Vitamins: B12 and folate · Multi-stepA strict vegan has macrocytic anaemia and paraesthesiae. His serum homocysteine and methylmalonic acid are both raised. What is the biochemical explanation for the neur…
- Vitamins: vitamin K · ApplicationA newborn who was not given vitamin K at birth bleeds from the umbilical stump on day 5. Which post-translational modification, dependent on vitamin K, is impaired?
- Vitamins: thiamine status assessment · ApplicationA malnourished man with chronic alcohol use has tachycardia and peripheral oedema. Which laboratory test best demonstrates functional thiamine deficiency?
- Vitamins: niacin and pellagra · ApplicationA farmer from a village whose staple is maize develops a symmetrical photosensitive rash over the neck (Casal necklace), diarrhoea and recent confusion. What best expla…
- Vitamins: pyridoxine and isoniazid · ApplicationA 50-year-old man on treatment for tuberculosis develops numbness and tingling of both feet. Deficiency of which vitamin is responsible, and by what mechanism?
- Vitamins: riboflavin deficiency · ApplicationA 30-year-old woman on a poor diet has angular stomatitis, cheilosis, a magenta tongue and seborrhoeic dermatitis of the nasolabial folds. Which test best confirms the…
- Vitamins: biotin deficiency · ApplicationA bodybuilder who eats about a dozen raw egg whites daily develops scaly dermatitis, hair thinning, lethargy and muscle pain. Which reaction is impaired?
- Vitamins: ascorbic acid and collagen · ApplicationA 70-year-old man living alone on a tea-and-toast diet has bleeding gums, perifollicular haemorrhages, corkscrew hairs and poor wound healing. Which biochemical process…
- Vitamins: visual cycle · ApplicationIn a dark-adapted rod, absorption of a photon by rhodopsin causes which primary photochemical change?
- Vitamins: hypervitaminosis A · ApplicationAn adult who has eaten large amounts of liver daily and taken vitamin A supplements develops headache, vomiting, blurred vision with papilloedema, bone pain, dry cracke…
- Vitamins: vitamin D resistance · Multi-stepAn 18-month-old child has rickets that does not respond to usual doses of vitamin D, sparse hair with alopecia totalis, hypocalcaemia, hypophosphataemia, high alkaline…
- Vitamins: vitamin E deficiency · ApplicationA 6-year-old with chronic fat malabsorption, very low LDL and chylomicrons and acanthocytes on the blood film develops progressive ataxia and loss of deep tendon reflex…
- Vitamins: folate functional test · ApplicationA woman has macrocytic anaemia with normal serum vitamin B12. Following an oral histidine load, which finding supports folate deficiency?
- Vitamins: B12 after ileal resection · Multi-stepA 40-year-old man had 80 cm of terminal ileum resected for Crohn disease 3 years ago. He now has macrocytic anaemia, paraesthesiae and impaired vibration sense. Serum f…
- Vitamins: vitamin A excess and retinoids · ApplicationA 19-year-old woman with severe nodulocystic acne is to start oral isotretinoin. She is counselled to use reliable contraception. Which mechanism underlies the teratoge…
- Vitamins: vitamin E deficiency · ApplicationA 6-year-old boy has fat malabsorption since infancy, acanthocytes on the blood film, very low plasma cholesterol and absent apolipoprotein B. He now has progressive at…
- Vitamins: pyridoxine and isoniazid · ApplicationA 45-year-old malnourished man on isoniazid-containing antituberculosis therapy complains of numbness and burning in both feet. Prophylactic pyridoxine would have preve…
- Vitamins: biotin and avidin · ApplicationA 26-year-old bodybuilder who consumes about a dozen raw egg whites daily presents with thinning hair, scaly periorificial dermatitis, conjunctivitis and depression. Wh…
- Vitamins · ApplicationWhich vitamin deficiency causes bleeding from impaired clotting-factor gamma carboxylation?
- Vitamins · ApplicationWhich vitamin deficiency causes night blindness?
- Vitamins · ApplicationDeficiency of which vitamin causes scurvy?
- Vitamins · ApplicationDeficiency of which vitamin causes rickets?
- Vitamins · ApplicationDeficiency of which vitamin causes pellagra?
- Vitamins · ApplicationDeficiency of which vitamin causes megaloblastic anemia and neuropathy?
- Vitamins · ApplicationWhat vitamin deficiency causes beriberi?
- Vitamins · ApplicationWhat vitamin deficiency causes cheilosis?
- Vitamins · ApplicationWhat vitamin is needed for transamination?
- Vitamins · ApplicationWhat vitamin is required for clotting factor activation?
- Vitamins · ApplicationWhich vitamin deficiency causes scurvy?
- Vitamins · ApplicationWhich vitamin is required for gamma-carboxylation of clotting factors?
- Vitamins · ApplicationWhat deficiency is associated with megaloblastic anemia and neurologic signs?
- Vitamins · ApplicationA child with impaired dark adaptation has xerophthalmia; deficiency of which vitamin is most likely?
- Vitamins · ApplicationWhich vitamin is required for calcium absorption and bone mineralization?
- Vitamins · ApplicationWhat deficiency can cause beriberi?
- Vitamins · ApplicationWhat vitamin deficiency causes pellagra?
- Vitamins · ApplicationWhat vitamin deficiency may cause cheilosis and glossitis?
- Vitamins · ApplicationWhat coenzyme form of vitamin B6 is important in amino acid metabolism?
- Vitamins · ApplicationWhich vitamin deficiency causes impaired collagen hydroxylation and scurvy?
- Vitamins · ApplicationWhich vitamin is required as a cofactor for gamma-carboxylation of clotting factors?
- Vitamins: thiamine · ApplicationWhich enzyme requires thiamine pyrophosphate as a cofactor and is impaired in Wernicke encephalopathy?
- Vitamins: biotin · ApplicationRaw egg-white consumption can cause deficiency of which vitamin because avidin binds it tightly?
- Vitamins: folate trap · Multi-stepIn vitamin B12 deficiency, which folate derivative accumulates because methionine synthase cannot regenerate tetrahydrofolate?
- Vitamins · ApplicationWhich vitamin deficiency causes megaloblastic anaemia with neurological impairment?
- Vitamins · ApplicationWhich vitamin acts as a coenzyme in carboxylation reactions?
- Vitamins: thiamine · ApplicationWhich enzyme requires thiamine pyrophosphate as a cofactor?
- Vitamins: niacin · ApplicationWhich clinical triad is associated with severe niacin deficiency?
- Vitamins: biotin · ApplicationBiotin acts as a cofactor for which type of biochemical reaction?
Nucleotide metabolism41
- Nucleotide metabolism · ApplicationA 4-year-old boy has intellectual disability, dystonia, self-mutilation and hyperuricaemia. Which enzyme is deficient?
- Nucleotide metabolism: pentostatin and adenosine deaminase · Multi-stepA drug used in hairy cell leukaemia causes lymphocytes to accumulate deoxyadenosine and dATP by inhibiting an enzyme whose inherited deficiency causes severe combined i…
- Nucleotide metabolism: end products of pyrimidine catabolism · ApplicationRapid cell turnover during chemotherapy releases large amounts of both purines and pyrimidines. Why does pyrimidine breakdown not cause crystal deposition like uric aci…
- Nucleotide metabolism: probenecid mechanism · ApplicationA man with recurrent gout attacks has a normal 24-hour urinary uric acid excretion, indicating renal underexcretion. He is started on probenecid. How does it lower seru…
- Nucleotide metabolism: febuxostat versus allopurinol · ApplicationA patient with gout develops a severe hypersensitivity rash to allopurinol. His physician prescribes febuxostat. Which property of febuxostat distinguishes it from allo…
- Nucleotide metabolism: effect of allopurinol on purine excretion · ApplicationA patient with gout is started on allopurinol. Serum uric acid falls, and a later urine analysis shows increased hypoxanthine and xanthine excretion. What explains the…
- Nucleotide metabolism: activation of 6-mercaptopurine · Multi-step6-Mercaptopurine is a prodrug. It inhibits de novo purine synthesis only after conversion to a thioinosine monophosphate nucleotide by an enzyme of the purine salvage p…
- Nucleotide metabolism: pemetrexed · ApplicationA patient with malignant pleural mesothelioma receives pemetrexed with folic acid and vitamin B12 supplementation to reduce toxicity. Pemetrexed is a folate analogue th…
- Nucleotide metabolism: reciprocal regulation of AMP and GMP synthesis · Multi-stepFrom inosine monophosphate, adenylate synthesis needs GTP, whereas guanylate synthesis needs ATP. What is the metabolic advantage of this arrangement?
- Nucleotide metabolism: convergence of purine catabolism at xanthine · ApplicationAdenine nucleotides are degraded via inosine and hypoxanthine, whereas guanine nucleotides are degraded via guanosine and guanine. Which compound is formed from both ro…
- Nucleotide metabolism: pyrazinamide and hyperuricaemia · ApplicationA 40-year-old man on antituberculosis treatment develops an acutely swollen first metatarsophalangeal joint, and serum uric acid is raised. Which drug from the regimen…
- Nucleotide metabolism: fructose and hyperuricaemia · Multi-stepA man with obesity drinks large quantities of fructose-sweetened beverages daily and has a raised serum urate and recurrent gout. Which mechanism links heavy fructose i…
- Nucleotide metabolism: CTP synthetase · ApplicationIn pyrimidine synthesis, UTP is converted to CTP by amination. Which compound provides the amino group in the human enzyme CTP synthetase?
- Nucleotide metabolism: urinary alkalinisation for uric acid stones · ApplicationA 55-year-old man with gout has a radiolucent renal calculus and persistently acidic urine (pH 5.2). Besides increasing fluid intake, which measure best reduces the ris…
- Nucleotide metabolism: duration of adenosine action · ApplicationA rapid intravenous bolus of adenosine terminates supraventricular tachycardia, but its effect lasts only seconds. Which process mainly accounts for its extremely short…
- Nucleotide metabolism: one-carbon donor for purine ring · ApplicationCarbons 2 and 8 of the purine ring are added in steps that use a folate coenzyme. Which tetrahydrofolate derivative serves as the donor?
- Nucleotide metabolism: hyperuricaemia in glycogen storage disease type I · Multi-stepA 2-year-old with fasting hypoglycaemia, hepatomegaly and lactic acidosis has a serum urate of 11 mg/dL. Which mechanism contributes to the hyperuricaemia?
- Nucleotide metabolism: neurological basis of Lesch-Nyhan syndrome · Multi-stepA boy with HGPRT deficiency has a normal urate on allopurinol, yet his dystonia and self-biting continue. What is the best explanation?
- Nucleotide metabolism: crystals in gout · ApplicationJoint fluid from a swollen first metatarsophalangeal joint is examined under compensated polarised light. Which finding confirms gout?
- Nucleotide metabolism: trimethoprim selectivity · ApplicationTrimethoprim blocks nucleotide synthesis in bacteria but is relatively safe for human cells. Which property accounts for this selectivity?
- Nucleotide metabolism: allopurinol hypersensitivity · ApplicationA man of Han Chinese descent develops a widespread blistering rash with mucosal ulceration four weeks after starting allopurinol. Which allele is known to predispose to…
- Nucleotide metabolism: secondary hyperuricaemia in psoriasis · ApplicationA man with extensive psoriasis, normal renal function and no medication has a serum urate of 9 mg/dL. Which mechanism most likely explains this?
- Nucleotide metabolism: CAD protein in pyrimidine synthesis · Multi-stepIn mammals, the first three steps of de novo pyrimidine synthesis are catalysed by a single multifunctional protein. Which three activities does it carry?
- Nucleotide metabolism: dihydroorotate dehydrogenase location · ApplicationWhich de novo pyrimidine synthetic enzyme is located on the inner mitochondrial membrane and passes electrons to ubiquinone?
- Nucleotide metabolism: reducing power for ribonucleotide reductase · Multi-stepRibonucleotide reductase converts ribonucleoside diphosphates to deoxyribonucleoside diphosphates. Which immediate reductant supplies electrons to the enzyme, and how i…
- Nucleotide metabolism: nucleoside linkage · ApplicationIn a purine nucleoside such as adenosine, C1 of ribose is joined by a beta-N-glycosidic bond to which ring atom of the base?
- Nucleotide metabolism: nitrogen sources in the purine ring · ApplicationIsotope-labelled amino acids are used to trace the purine ring. Which amino acid provides nitrogen 1 of the ring?
- Nucleotide metabolism: PRPP synthetase regulation · Multi-stepPRPP synthetase supplies the substrate for the first committed step of purine synthesis. Which statement correctly describes its control in normal cells?
- Nucleotide metabolism: xanthine oxidase in reperfusion injury · Multi-stepIn ischaemic tissue ATP is degraded and hypoxanthine accumulates. When blood flow returns, why is free radical injury produced?
- Nucleotide metabolism · ApplicationWhat base pairs with adenine in DNA?
- Nucleotide metabolism · ApplicationWhat enzyme adds nucleotides during DNA replication?
- Nucleotide metabolism · ApplicationWhich drug reduces uric acid formation by inhibiting xanthine oxidase?
- Nucleotide metabolism · ApplicationWhat base is present in RNA instead of thymine?
- Nucleotide metabolism · ApplicationWhat enzyme synthesizes RNA using a DNA template?
- Nucleotide metabolism · ApplicationWhat enzyme joins Okazaki fragments during DNA replication?
- Nucleotide metabolism · ApplicationWhat enzyme is inhibited by methotrexate?
- Nucleotide metabolism · ApplicationWhich drug lowers uric acid production by inhibiting xanthine oxidase?
- Nucleotide metabolism: Lesch-Nyhan syndrome · ApplicationSelf-injury, dystonia and hyperuricaemia in a boy result from failure of which purine salvage enzyme?
- Nucleotide metabolism: allopurinol · ApplicationAllopurinol lowers uric acid by inhibiting which enzyme?
- Nucleotide metabolism: gout · ApplicationAllopurinol lowers uric acid in gout by inhibiting which enzyme?
- Nucleotide metabolism: Lesch-Nyhan syndrome · ApplicationA boy has self-injurious behavior, dystonia, hyperuricemia, and orange urate crystals in diapers. Which enzyme deficiency is most likely?
Molecular biology and genetics37
- Molecular biology and genetics: trinucleotide repeats · Multi-stepA boy has intellectual disability, a long face and macro-orchidism. Analysis shows more than 200 CGG repeats in the FMR1 gene. Through which mechanism does this cause d…
- Molecular biology and genetics: cytogenetic methods · ApplicationA bone marrow sample from a patient with suspected chronic myeloid leukaemia yields too few dividing cells for karyotyping. Which technique can still detect the BCR-ABL…
- Molecular biology and genetics: tryptophan operon attenuation · Multi-stepIn E. coli, when tryptophan is plentiful, transcription of the trp operon stops after initiation, before the structural genes are transcribed. Which mechanism accounts…
- Molecular biology and genetics: MELAS · ApplicationA 14-year-old has recurrent stroke-like episodes, lactic acidosis, seizures and short stature. Muscle biopsy shows ragged red fibres, and his mother has migraine and de…
- Molecular biology and genetics: APC and beta-catenin · ApplicationA 19-year-old has hundreds of adenomatous polyps in the colon and a family history of colorectal cancer. A germline mutation of the APC gene is found. Which molecular c…
- Molecular biology and genetics: JAK2 V617F mutation · ApplicationA 55-year-old man has a raised haemoglobin, itching after a hot bath and splenomegaly. Bone marrow shows panmyelosis. A somatic mutation in which gene is found in most…
- Molecular biology and genetics: Angelman syndrome · Multi-stepA 3-year-old has severe developmental delay, absent speech, ataxic gait, seizures and frequent unprovoked laughter. FISH shows a deletion at 15q11-q13. On which parenta…
- Molecular biology and genetics: balanced translocation carriers · Multi-stepA couple has had three first-trimester miscarriages. Both partners are phenotypically normal, and karyotyping shows that the woman carries a balanced reciprocal translo…
- Molecular biology and genetics: cell-free fetal DNA screening · ApplicationNon-invasive prenatal testing for trisomy 21 analyses cell-free DNA in the mother's plasma from about the tenth week. From which source does the fetal fraction of this…
- Molecular biology and genetics: t(8;14) in Burkitt lymphoma · ApplicationA 7-year-old child has a rapidly enlarging jaw mass. Biopsy shows sheets of medium-sized lymphoid cells with tingible-body macrophages giving a starry-sky pattern, and…
- Molecular biology and genetics: Friedreich ataxia · ApplicationA 14-year-old has progressive gait ataxia, absent ankle reflexes, scoliosis, hypertrophic cardiomyopathy and new-onset diabetes. Genetic testing shows an expanded intro…
- Molecular biology and genetics: Turner syndrome · ApplicationA 15-year-old girl has short stature, a webbed neck, widely spaced nipples, primary amenorrhoea and a bicuspid aortic valve. Which karyotype and hormonal finding are ex…
- Molecular biology and genetics: cholera toxin and Gs · ApplicationIn severe cholera, the toxin of Vibrio cholerae causes massive intestinal secretion by raising cAMP in enterocytes. Which post-translational change in a signalling prot…
- Molecular biology and genetics: pertussis toxin and Gi · ApplicationPertussis toxin raises cAMP in airway cells by modifying a G protein. Which modification explains this?
- Molecular biology and genetics: antisense therapy in spinal muscular atrophy · Multi-stepAn infant with hypotonia and tongue fasciculations is found to have a homozygous deletion of SMN1. Intrathecal nusinersen, an antisense oligonucleotide, is started. How…
- Molecular biology and genetics: CYP2C19 and clopidogrel · ApplicationA patient with a drug-eluting coronary stent on clopidogrel develops stent thrombosis. Genotyping shows two CYP2C19 loss-of-function alleles. Why is the antiplatelet ef…
- Molecular biology and genetics: nonsense-mediated mRNA decay · Multi-stepA patient is homozygous for a single-base change that creates an early stop codon in a gene. Cells contain very little mRNA from this gene. Which cellular process expla…
- Molecular biology and genetics: CDK4/6 inhibition and Rb · Multi-stepA woman with hormone receptor-positive breast cancer is started on palbociclib, a CDK4/6 inhibitor. Which event is blocked, arresting cells in G1?
- Molecular biology and genetics: zidovudine as a chain terminator · ApplicationZidovudine is a nucleoside analogue used against HIV. Why does its incorporation by reverse transcriptase stop viral DNA synthesis?
- Molecular biology and genetics: insertional mutagenesis in gene therapy · Multi-stepSome children with X-linked severe combined immunodeficiency who received gene therapy with a retroviral vector later developed T-cell leukaemia. Which mechanism was re…
- Molecular biology and genetics: CpG mutation hotspots · Multi-stepSingle-base C to T transitions occur far more often at CpG dinucleotides than elsewhere in human genes. Why?
- Molecular biology and genetics: rho-dependent transcription termination · ApplicationIn E. coli, transcription of some genes ends without a stem-loop followed by a run of uridines. Which protein terminates transcription at these genes?
- Molecular biology and genetics: dominant-negative mutation · Multi-stepA tumour suppressor protein functions as a tetramer. A heterozygous missense mutation in its DNA-binding domain abolishes far more activity than deleting one allele wou…
- Molecular biology and genetics: BCR-ABL fusion · ApplicationA 45-year-old has splenomegaly, a leucocyte count of 150,000 per microlitre with myeloid cells at all stages of maturation, and t(9;22) on karyotype. What is the functi…
- Molecular biology and genetics: Lynch syndrome · Multi-stepA 38-year-old has colon cancer. His mother had endometrial cancer and his uncle had colon cancer at 45. The tumour shows microsatellite instability. Which DNA repair pa…
- Molecular biology and genetics: non-homologous end joining · Multi-stepAn infant has severe combined immunodeficiency with absent T and B cells and marked radiosensitivity. Sequencing shows a mutation in Artemis, which is needed for V(D)J…
- Molecular biology and genetics: chromosomal mosaicism · ApplicationA girl with mild features of Down syndrome has 47,XX,+21 in 30 percent of cultured blood cells and 46,XX in the rest. How did this arise?
- Molecular biology and genetics: eIF2 phosphorylation in reticulocytes · Multi-stepIn haem-deficient reticulocytes, globin synthesis stops because the haem-regulated inhibitor kinase becomes active. Which initiation factor does it phosphorylate?
- Molecular biology and genetics: cDNA cloning · ApplicationA researcher wants bacteria to produce a human protein, but bacteria cannot splice introns. Which DNA should be cloned into the expression vector?
- Molecular biology and genetics: tetracycline mechanism · ApplicationA teenager with acne is treated with doxycycline. Which step of bacterial protein synthesis does the drug block?
- Molecular biology and genetics: whole-exome sequencing · ApplicationA child has an undiagnosed syndromic intellectual disability. Karyotype and chromosomal microarray are normal. Which test is best suited to find a single-gene variant b…
- Molecular biology and genetics: chromatin states · ApplicationWhich pattern characterises transcriptionally silent heterochromatin?
- Molecular biology and genetics: haploinsufficiency · ApplicationIn an autosomal dominant disorder, a heterozygous whole-gene deletion leaves a single working allele that produces only 50 percent of the normal protein, which is insuf…
- Molecular biology and genetics: NAT2 and isoniazid · ApplicationA man with tuberculosis develops peripheral neuropathy on standard-dose isoniazid. Genotyping shows variants that reduce hepatic N-acetylation of the drug. Which pharma…
- Molecular biology and genetics: UGT1A1 and irinotecan · Multi-stepA man with colon cancer develops severe neutropenia and diarrhoea after irinotecan. He is homozygous for the UGT1A1*28 variant. What is the mechanism?
- Molecular biology and genetics: VHL and HIF · Multi-stepA 30-year-old has retinal and cerebellar haemangioblastomas and a clear cell renal carcinoma. A germline VHL mutation is found. What is the molecular consequence?
- Molecular biology and genetics: single large mtDNA deletion · Multi-stepA 20-year-old has ptosis, ophthalmoplegia, pigmentary retinopathy and heart block. Muscle biopsy shows ragged red fibres and a single large deletion of mitochondrial DN…
Vitamins and minerals36
- Vitamins and minerals: magnesium · ApplicationA patient on a long-term proton pump inhibitor has tetany. Serum calcium is low and does not rise with calcium infusion alone. Serum magnesium is very low. Why is the c…
- Vitamins and minerals · ApplicationTryptophan can be converted to niacin in the body. About how many milligrams of dietary tryptophan are equivalent to 1 mg of niacin?
- Vitamins and minerals: beta-carotene cleavage · ApplicationBeta-carotene is the most efficient provitamin A carotenoid. What happens to it in the intestinal mucosa?
- Vitamins and minerals: zinc and retinol-binding protein · Multi-stepA child with chronic diarrhoea and night blindness has a low serum retinol despite normal liver stores of vitamin A and a normal diet. His serum zinc is also low. Why d…
- Vitamins and minerals: carotenaemia versus jaundice · ApplicationA toddler on a diet rich in carrots and pumpkin has yellow-orange palms and soles. The sclerae are white and the urine is of normal colour. What is the explanation?
- Vitamins and minerals: warfarin and the vitamin K cycle · ApplicationA man with atrial fibrillation on long-term warfarin has a prolonged prothrombin time. Warfarin impairs clotting factor activation by blocking which step in the vitamin…
- Vitamins and minerals: warfarin-induced skin necrosis · Multi-stepA woman is started on warfarin without heparin cover for a deep vein thrombosis. On day 4 she develops painful, well-demarcated skin necrosis over the breasts and thigh…
- Vitamins and minerals: Bitot spots in vitamin A deficiency · Multi-stepA malnourished 4-year-old has poor vision in dim light and foamy, triangular, greyish patches on the bulbar conjunctiva that do not wet with tears. Which histological c…
- Vitamins and minerals: Schilling test interpretation · Multi-stepIn a Schilling test, a patient with macrocytic anaemia excretes very little radiolabelled cobalamin in the urine after an oral dose. The result becomes normal when the…
- Vitamins and minerals: refeeding syndrome · Multi-stepA severely malnourished 24-year-old woman with anorexia nervosa is started on aggressive enteral feeding. On day 3 she develops muscle weakness, an arrhythmia and confu…
- Vitamins and minerals: zinc therapy in Wilson disease · Multi-stepA 19-year-old with Wilson disease has completed initial chelation and is maintained on oral zinc salts. How does zinc limit copper accumulation?
- Vitamins and minerals: laboratory diagnosis of Wilson disease · ApplicationA 16-year-old has tremor, personality change, chronic hepatitis and a Coombs-negative haemolytic episode. Slit-lamp examination shows golden-brown corneal rings. Which…
- Vitamins and minerals: X-linked hypophosphataemic rickets · Multi-stepA 3-year-old boy has bowed legs and short stature. Rickets persists despite usual doses of vitamin D. Serum calcium and PTH are normal, phosphate is low and alkaline ph…
- Vitamins and minerals: all-trans retinoic acid in promyelocytic leukaemia · ApplicationA 30-year-old has bleeding, pancytopenia and a prolonged prothrombin time. Marrow shows abnormal promyelocytes with Auer rods and t(15;17). A vitamin A derivative is ad…
- Vitamins and minerals: vitamin K malabsorption in biliary obstruction · ApplicationA 55-year-old man with obstructive jaundice from a pancreatic head tumour has a prolonged prothrombin time. It corrects within 24 hours of an intramuscular vitamin K in…
- Vitamins and minerals: biochemical profile of osteomalacia · ApplicationA 38-year-old woman who wears fully covering clothing and has little sun exposure has diffuse bone pain, proximal muscle weakness and pseudofractures on radiograph. Whi…
- Vitamins and minerals: folic acid masking cobalamin deficiency · Multi-stepA strict vegan with macrocytic anaemia and distal paraesthesiae is given folic acid alone. His haemoglobin rises, but six months later he has gait ataxia and loss of vi…
- Vitamins and minerals: iron overload in thalassaemia intermedia · Multi-stepA 12-year-old with untreated non-transfusion-dependent beta-thalassaemia intermedia develops progressive iron overload and a raised ferritin. Which mechanism is mainly…
- Vitamins and minerals: wet beriberi · ApplicationA malnourished man living on polished rice has breathlessness, bilateral leg oedema, warm extremities, a wide pulse pressure and a high cardiac output. Deficiency of wh…
- Vitamins and minerals: measuring vitamin D status · ApplicationA clinic wants a single blood test to judge a patient's vitamin D stores. Which measurement is most appropriate, and why?
- Vitamins and minerals: hypercarotenaemia · ApplicationA 2-year-old fed large daily servings of mashed carrot and papaya has yellow-orange palms, soles and nasolabial folds. The sclerae are white and serum bilirubin is norm…
- Vitamins and minerals: holocarboxylase synthetase deficiency · Multi-stepA 3-week-old infant has a scaly erythematous rash, alopecia, hypotonia, vomiting and ketolactic acidosis. Urine contains 3-hydroxyisovalerate and methylcitrate, and bio…
- Vitamins and minerals: fish tapeworm and cobalamin · ApplicationA man from a lakeside community who regularly eats raw freshwater fish has macrocytic anaemia, low serum cobalamin and normal folate. Stool shows operculated eggs. How…
- Vitamins and minerals: nitrous oxide and methionine synthase · Multi-stepA 24-year-old who inhales nitrous oxide cartridges daily has paraesthesia, impaired vibration sense and a broad-based gait. Serum cobalamin is low-normal and plasma hom…
- Vitamins and minerals: acrodermatitis enteropathica · Multi-stepAn infant develops vesiculobullous lesions around the mouth and anus, diarrhoea and hair loss soon after weaning from breast milk. Serum alkaline phosphatase is low. Or…
- Vitamins and minerals: Wolff-Chaikoff effect · ApplicationA patient with Graves disease is given a large dose of Lugol iodine before thyroidectomy and thyroid hormone synthesis falls within days. Which effect explains this?
- Vitamins and minerals: pyridoxal phosphate and sideroblastic anaemia · ApplicationA man with tuberculosis on long-term isoniazid develops microcytic hypochromic anaemia with ring sideroblasts in the marrow and a raised serum ferritin. Which reaction…
- Vitamins and minerals: Pendred syndrome · Multi-stepA child has congenital sensorineural deafness and a goitre but remains euthyroid with normal thyroid hormone levels. Inner ear imaging shows an enlarged vestibular aque…
- Vitamins and minerals: nuclear receptor partner · ApplicationThe vitamin D receptor and the retinoic acid receptor both act on DNA only after pairing with a common partner, whereas oestrogen, glucocorticoid and androgen receptors…
- Vitamins and minerals: hungry bone syndrome · Multi-stepThree days after parathyroidectomy for long-standing primary hyperparathyroidism with severe bone disease, a patient has perioral tingling and carpopedal spasm. Serum c…
- Vitamins and minerals: pseudohypoparathyroidism · Multi-stepA short 10-year-old with a round face, short fourth metacarpals and subcutaneous calcifications has tetany. Serum calcium is low, phosphate is high and PTH is markedly…
- Vitamins and minerals: iron regulatory proteins · Multi-stepA cell becomes iron deficient. Iron regulatory protein binds iron-responsive elements on messenger RNA. Which change in protein synthesis follows?
- Vitamins and minerals: hepatic storage of vitamin A · ApplicationA man who has taken very large doses of vitamin A for several years develops hepatomegaly, and biopsy shows perisinusoidal fibrosis with fat-laden cells. Which cells no…
- Vitamins and minerals: dietary goitrogens · ApplicationVillagers who eat poorly processed cassava as a staple have goitre even though iodine intake is borderline adequate. Which mechanism contributes?
- Vitamins and minerals: vitamin D-dependent rickets type 1 · Multi-stepA 9-month-old has rickets with hypocalcaemia, raised PTH and raised alkaline phosphatase. Serum 25-hydroxyvitamin D is normal, calcitriol is low and the child responds…
- Vitamins and minerals: niacin flushing · ApplicationA man with dyslipidaemia is started on nicotinic acid in pharmacological doses and complains of intense facial flushing and warmth. Which mediator accounts for the flus…
Biomolecules and enzymes24
- Biomolecules and enzymes: lysosomal storage · Multi-stepA 3-year-old boy has coarse facies, hepatosplenomegaly, joint stiffness and aggressive behaviour. His corneas are clear and a maternal uncle had the same illness. Which…
- Biomolecules and enzymes: uncompetitive inhibition on a double reciprocal plot · Multi-stepIn an enzyme assay, a plot of 1/v against 1/[S] is drawn with and without an inhibitor. The two lines are parallel, and the inhibited line lies above the control. Which…
- Biomolecules and enzymes: gel filtration chromatography · ApplicationA mixture of proteins of 150 kDa, 66 kDa and 14 kDa is passed through a gel filtration column. In which order do they leave the column?
- Biomolecules and enzymes: cation-exchange chromatography of amino acids · Multi-stepA mixture of alanine, aspartate, glutamate and lysine at pH 7 is loaded onto a cation-exchange resin that carries negatively charged groups. The column is then eluted w…
- Biomolecules and enzymes: digoxin and the sodium-potassium ATPase · ApplicationA man with heart failure on digoxin is started on a loop diuretic and develops nausea, visual disturbance and arrhythmia. His serum potassium is 2.8 mmol/L. How does hy…
- Biomolecules and enzymes: intermediate filament markers · ApplicationA 6-year-old child has a rapidly growing orbital mass. Biopsy shows small round cells with some elongated strap-shaped cells showing cross-striations. Immunostaining fo…
- Biomolecules and enzymes: dynein defect in primary ciliary dyskinesia · ApplicationA young man has chronic sinusitis, recurrent bronchiectasis, dextrocardia and infertility because his sperm are immotile. Electron microscopy of his cilia is most likel…
- Biomolecules and enzymes: integrin defect in Glanzmann thrombasthenia · ApplicationA child has recurrent mucocutaneous bleeding with a normal platelet count and normal PT and aPTT. Platelets fail to aggregate with ADP, collagen and epinephrine, but ag…
- Biomolecules and enzymes: aquaporin-2 and lithium · Multi-stepA man with bipolar disorder on long-term lithium passes large volumes of dilute urine. After water deprivation and after desmopressin, urine osmolality remains low. Whi…
- Biomolecules and enzymes: calcium-calmodulin and phosphorylase kinase · Multi-stepDuring a sprint, glycogen breakdown in skeletal muscle rises within seconds, before adrenaline-driven signalling can act. Which signal directly links contraction to act…
- Biomolecules and enzymes: GPI anchor defect in PNH · Multi-stepA 28-year-old woman has episodic dark urine in the morning, venous thrombosis and pancytopenia. Flow cytometry shows loss of CD55 and CD59 on her red cells. Which defec…
- Biomolecules and enzymes: heparin and antithrombin · ApplicationA patient on unfractionated heparin has a prolonged aPTT. The drug acts by binding, through a specific sulfated pentasaccharide sequence, to which plasma protein and en…
- Biomolecules and enzymes: gamma-carboxyglutamate · ApplicationA patient on warfarin has factors II, VII, IX and X that cannot bind calcium and attach to phospholipid surfaces. Which modified amino acid residue is deficient in thes…
- Biomolecules and enzymes: kinesin and axonal transport · ApplicationVesicles loaded with neurotransmitter-synthesising enzymes must travel from the neuronal cell body along microtubules to the axon terminal. Which motor protein drives t…
- Biomolecules and enzymes: Anfinsen experiment · Multi-stepRibonuclease treated with urea and beta-mercaptoethanol loses all activity. When both agents are removed slowly, activity returns and the correct disulfide bonds re-for…
- Biomolecules and enzymes: hydrophobic effect in folding · ApplicationIn a water-soluble globular protein, nonpolar side chains such as leucine, isoleucine and phenylalanine are mostly buried in the interior. Which force chiefly drives th…
- Biomolecules and enzymes: lysosomal beta-galactosidase · Multi-stepA 6-month-old infant has coarse facies, hepatosplenomegaly, skeletal dysplasia, hypotonia and a cherry-red macular spot. Storage of GM1 ganglioside and keratan sulfate…
- Biomolecules and enzymes: mutarotation of glucose · ApplicationA freshly prepared solution of pure alpha-D-glucose shows a specific rotation of +112 degrees, which slowly drifts to +52.7 degrees and then stays constant. Which chang…
- Biomolecules and enzymes: Morquio syndrome · ApplicationA 6-year-old child has a short trunk, pectus carinatum, knock knees, odontoid hypoplasia and normal intelligence. Urine contains excess keratan sulfate. Which enzyme is…
- Biomolecules and enzymes: disulfiram and aldehyde dehydrogenase · ApplicationA man receiving aversion therapy for alcohol dependence develops flushing, palpitations, headache and vomiting after taking a small amount of alcohol. Which enzyme has…
- Biomolecules and enzymes: advanced glycation end products · ApplicationIn a patient with long-standing poorly controlled diabetes, glucose attaches without enzymes to lysine residues of long-lived proteins such as collagen, and later rearr…
- Biomolecules and enzymes: substrate reduction therapy in Gaucher disease · ApplicationAn adult with type 1 Gaucher disease is given an oral drug such as eliglustat that does not replace the missing enzyme. Instead it lowers production of the lipid that a…
- Biomolecules and enzymes: congenital disorder of glycosylation type Ib · Multi-stepAn infant has protein-losing enteropathy, hepatic fibrosis, hypoglycaemia and a coagulopathy, but normal development and no cerebellar hypoplasia. Transferrin isoelectr…
- Biomolecules and enzymes: cholesterol and membrane fluidity · ApplicationCholesterol is intercalated among phospholipids of a plasma membrane. At body temperature, what is the main effect of the cholesterol on the bilayer?
Enzymes17
- Enzymes: allosteric regulation of aspartate transcarbamoylase · Multi-stepAspartate transcarbamoylase of E. coli gives a sigmoidal curve when reaction velocity is plotted against aspartate concentration. When CTP is added to the assay, the cu…
- Enzymes: units and specific activity · Multi-stepA researcher incubates 0.2 mL of a tissue extract (4 mg protein per mL) with substrate. In 6 minutes, 24 micromoles of product are formed. What is the specific activity…
- Enzymes · ApplicationCompetitive inhibition increases which parameter?
- Enzymes · ApplicationWhat does a lower Km generally indicate?
- Enzymes · ApplicationWhat does Vmax depend on?
- Enzymes · ApplicationWhat does a lower Km generally indicate for an enzyme substrate?
- Enzymes · ApplicationWhat parameter rises when enzyme concentration is increased with abundant substrate?
- Enzymes · ApplicationWhat type of inhibition can usually be overcome by increasing substrate concentration?
- Enzymes · ApplicationWhat is an enzyme cofactor that is an organic molecule called?
- Enzymes · ApplicationWhat happens to Vmax in pure competitive inhibition?
- Enzymes · ApplicationWhat happens to both Km and Vmax in noncompetitive inhibition?
- Enzymes · ApplicationWhat does the Km of an enzyme-substrate reaction represent?
- Enzymes · ApplicationWhat is the usual effect of a competitive enzyme inhibitor?
- Enzymes: irreversible inhibition · ApplicationOrganophosphate poisoning irreversibly inhibits acetylcholinesterase by covalently modifying which amino-acid residue at its active site?
- Enzymes: vitamin K · ApplicationWarfarin therapy impairs gamma-carboxylation of clotting factors. Which amino acid normally undergoes this modification?
- Enzymes · ApplicationWhat does Vmax depend on when substrate is saturating?
- Enzymes · ApplicationWhich enzyme class transfers phosphate groups from ATP to a substrate?
Molecular biology15
- Molecular biology · ApplicationXeroderma pigmentosum is due to a defect in which DNA repair pathway?
- Molecular biology: transcription · ApplicationA patient on antituberculous therapy is given a drug that inhibits bacterial DNA-dependent RNA polymerase. Which statement describes the mechanism?
- Molecular biology: gene regulation · ApplicationIn the lac operon of E. coli, what happens when glucose is absent and lactose is present?
- Molecular biology: prokaryotic DNA replication · ApplicationAn E. coli mutant has a tenfold higher spontaneous mutation rate. Studies show loss of the epsilon subunit, which provides 3' to 5' exonuclease proofreading to the main…
- Molecular biology: translation initiation · ApplicationA bacterial polycistronic mRNA encodes three proteins, and ribosomes initiate translation at each start codon independently. Which feature makes this possible?
- Molecular biology: RNA interference · ApplicationPatisiran, a double-stranded small interfering RNA given intravenously for hereditary transthyretin amyloidosis, lowers circulating transthyretin. Which mechanism appli…
- Molecular biology: epigenetic regulation · ApplicationA patient with cutaneous T cell lymphoma receives vorinostat, an inhibitor of histone deacetylases. What is the effect of increased histone lysine acetylation on chroma…
- Molecular biology · ApplicationWhat process produces an RNA copy from a DNA template?
- Molecular biology · ApplicationWhat process uses mRNA to synthesize a protein?
- Molecular biology · ApplicationWhat process removes introns from precursor mRNA?
- Molecular biology · ApplicationWhich base-pairing rule applies to double-stranded DNA?
- Molecular biology · ApplicationWhat is the main function of DNA polymerase during replication?
- Molecular biology · ApplicationWhich process removes introns from eukaryotic precursor mRNA?
- Molecular biology · ApplicationDuring protein translation, what is a codon on messenger RNA?
- Molecular biology: PCR · ApplicationWhich component is required in polymerase chain reaction to synthesize new DNA strands at high temperature?
Lipoproteins13
- Lipoproteins: dyslipidaemia · ApplicationA child has recurrent abdominal pain, eruptive xanthomas and lipaemia retinalis. The plasma is creamy, with a milky layer on standing at 4 degrees and a clear infranata…
- Lipoproteins: PCSK9 inhibition · ApplicationA 28-year-old man has an LDL cholesterol of 310 mg/dL, Achilles tendon xanthomas and a father who had a myocardial infarction at 40. His LDL remains high despite maxima…
- Lipoproteins: abetalipoproteinaemia · ApplicationA 3-year-old child has chronic steatorrhoea, failure to thrive, acanthocytes on the blood film and very low plasma cholesterol and triglycerides. Later he develops atax…
- Lipoproteins: LCAT and reverse cholesterol transport · ApplicationA 35-year-old man has corneal clouding, normocytic anaemia with target cells, proteinuria and a very low HDL cholesterol. The enzyme deficient in this condition perform…
- Lipoproteins: familial dysbetalipoproteinaemia · ApplicationA 40-year-old man has orange-yellow creases in the palms, tuberoeruptive xanthomas over the elbows, total cholesterol 420 mg/dL and triglycerides 450 mg/dL. Lipoprotein…
- Lipoproteins: Tangier disease · ApplicationA 14-year-old boy has enlarged, yellow-orange tonsils, mild hepatosplenomegaly and a peripheral neuropathy. Plasma HDL cholesterol is under 5 mg/dL, LDL cholesterol is…
- Lipoproteins: familial defective apoB-100 · Multi-stepA 32-year-old man has LDL cholesterol 300 mg/dL and tendon xanthomas, as did his father. LDL receptor expression on his cells is normal and the LDLR and PCSK9 genes are…
- Lipoproteins · ApplicationWhich lipoprotein carries dietary triglyceride from intestine?
- Lipoproteins · ApplicationWhich apolipoprotein mediates hepatic remnant uptake?
- Lipoproteins · ApplicationWhich lipoprotein participates in reverse cholesterol transport?
- Lipoproteins: familial hypercholesterolaemia · ApplicationTendon xanthomas and premature coronary disease with markedly raised LDL most commonly result from defective uptake through which receptor?
- Lipoproteins · ApplicationWhich apolipoprotein activates lipoprotein lipase to hydrolyze triglycerides in chylomicrons and VLDL?
- Lipoproteins: familial hypercholesterolemia · ApplicationA teenager has tendon xanthomas, very high LDL cholesterol, and early family history of myocardial infarction. Which defect is likely?
Amino acids11
- Amino acids: isoelectric point · Multi-stepLysine has pKa values of 2.2 (alpha carboxyl), 9.0 (alpha amino) and 10.5 (side chain amino). What is its isoelectric point?
- Amino acids · ApplicationWhich amino acid becomes conditionally essential in phenylketonuria?
- Amino acids · ApplicationWhich amino acid is precursor of serotonin?
- Amino acids · ApplicationWhich amino acid is precursor of catecholamines?
- Amino acids · ApplicationWhat amino acid is precursor of nitric oxide?
- Amino acids · ApplicationWhat amino acid is precursor of histamine?
- Amino acids · ApplicationWhich amino acid is the main nitrogen donor in many transamination reactions?
- Amino acids · ApplicationWhich amino acid is the biochemical precursor of nitric oxide in vascular endothelium?
- Amino acids: urea cycle · Multi-stepA newborn has hyperammonemia, respiratory alkalosis, and elevated urinary orotic acid without megaloblastic anemia. Which enzyme defect is most likely?
- Amino acids: phenylketonuria · ApplicationWhich dietary intervention is central in phenylketonuria?
- Amino acids: maple syrup urine disease · ApplicationDeficiency of branched-chain alpha-ketoacid dehydrogenase causes accumulation of which amino acids?
Oxidative phosphorylation10
- Oxidative phosphorylation: oligomycin and DNP · Multi-stepIn an oxygen electrode, isolated mitochondria oxidising succinate with ADP and phosphate consume oxygen briskly. Oligomycin stops oxygen consumption. Adding 2,4-dinitro…
- Oxidative phosphorylation · ApplicationWhich complex directly reduces oxygen to water?
- Oxidative phosphorylation · ApplicationWhich poison inhibits cytochrome c oxidase?
- Oxidative phosphorylation · ApplicationWhat directly drives ATP synthase?
- Oxidative phosphorylation · ApplicationWhere is the electron transport chain located in eukaryotic cells?
- Oxidative phosphorylation · ApplicationWhat is the terminal electron acceptor in aerobic respiration?
- Oxidative phosphorylation · ApplicationWhat molecule directly drives ATP synthase in mitochondria?
- Oxidative phosphorylation: cyanide · ApplicationCyanide causes rapid cellular hypoxia despite normal arterial oxygen content by inhibiting which electron-transport-chain complex?
- Oxidative phosphorylation · ApplicationWhich complex of the electron-transport chain does not pump protons across the inner mitochondrial membrane?
- Oxidative phosphorylation: uncoupling · ApplicationWhat is the effect of an uncoupling agent on oxygen consumption and heat production?
Genetics9
- Genetics: cystic fibrosis CFTR mutation · ApplicationA 2-year-old child with recurrent chest infections and steatorrhoea has a sweat chloride of 90 mmol/L. Genotyping shows homozygosity for the deltaF508 mutation. What is…
- Genetics: penetrance and expressivity · Multi-stepIn a family with an autosomal dominant disorder, genetic testing identifies 20 individuals who carry the pathogenic variant. Of these, 17 have clinical features and 3 a…
- Genetics · ApplicationWhat is the usual inheritance pattern of cystic fibrosis?
- Genetics · ApplicationWhat is a mutation that changes one amino acid to another called?
- Genetics · ApplicationWhat is a deletion mutation?
- Genetics · ApplicationWhich inheritance pattern shows affected fathers transmitting a trait to all daughters but no sons?
- Genetics: mitochondrial inheritance · ApplicationWhich inheritance pattern is typical of mitochondrial disorders?
- Genetics: anticipation · ApplicationWhat genetic mechanism underlies anticipation in Huntington disease?
- Genetics: genomic imprinting · ApplicationWhich disorder can arise from loss of paternal gene expression on chromosome 15?
Heme metabolism9
- Heme metabolism · ApplicationWhat pigment gives bile its yellow-green color?
- Heme metabolism · ApplicationWhat protein stores iron inside cells?
- Heme metabolism · ApplicationWhat enzyme converts heme to biliverdin?
- Heme metabolism · ApplicationWhat iron transport protein circulates in plasma?
- Heme metabolism · ApplicationWhat enzyme inserts iron into protoporphyrin IX during heme synthesis?
- Heme metabolism · ApplicationWhat protein binds free hemoglobin in plasma after intravascular hemolysis?
- Heme metabolism: porphyria · ApplicationA patient has abdominal pain, neuropathy and darkening urine after barbiturate exposure, but no photosensitivity. Which enzyme is most likely deficient?
- Heme metabolism: porphyria · ApplicationA patient has episodic abdominal pain, neuropathy, psychiatric symptoms, and darkening urine without photosensitivity. Which porphyria is most likely?
- Heme metabolism: bilirubin · ApplicationUnconjugated bilirubin is carried in plasma mainly bound to which protein?
Cholesterol metabolism8
- Cholesterol metabolism: bile acid sequestrants · Multi-stepA 45-year-old man with raised LDL cholesterol is started on cholestyramine. Which mechanism explains the fall in his LDL cholesterol?
- Cholesterol metabolism: HMG-CoA reductase · ApplicationHepatic cholesterol synthesis shows a diurnal rhythm with a peak at night, which is why shorter-acting lipid-lowering tablets are advised in the evening. Activity of wh…
- Cholesterol metabolism: HMG-CoA reductase · ApplicationIn a fasting subject glucagon raises cAMP, and the rate-limiting enzyme of cholesterol synthesis becomes phosphorylated and less active; insulin reverses this change. W…
- Cholesterol metabolism: HMG-CoA reductase · Multi-stepWhen cellular sterol content is high, an endoplasmic reticulum enzyme of the cholesterol pathway binds Insig, is ubiquitinated and is degraded, while SREBP-2 stays reta…
- Cholesterol metabolism: HMG-CoA reductase · Multi-stepA drug blocks the pathway that supplies farnesyl pyrophosphate. Cells lose not only sterols but also ubiquinone, dolichol and the isoprenyl anchors of Ras-family protei…
- Cholesterol metabolism: HMG-CoA reductase · Multi-stepIn a sterol-depleted hepatocyte, SREBP-2 travels to the Golgi, is cleaved, and enters the nucleus. Transcription of the LDL receptor gene rises, along with that of whic…
- Cholesterol metabolism: HMG-CoA reductase · ApplicationA patient takes a red yeast rice supplement for high cholesterol. Its active component, monacolin K, is chemically identical to lovastatin. Which enzyme does it inhibit…
- Cholesterol metabolism · ApplicationWhich enzyme is the rate-limiting target of statins in cholesterol synthesis?
Glycolysis8
- Glycolysis: muscle phosphofructokinase deficiency · Multi-stepA 25-year-old man has exercise intolerance with cramps that worsen if he takes a glucose-rich snack before exertion. He also has mild chronic haemolysis with raised ret…
- Glycolysis: pyruvate kinase deficiency · Multi-stepA child has chronic non-spherocytic haemolytic anaemia, splenomegaly and a negative Coombs test. Red cell pyruvate kinase activity is low. Which finding is expected in…
- Glycolysis: arsenate and ATP yield · Multi-stepArsenate can substitute for inorganic phosphate at glyceraldehyde-3-phosphate dehydrogenase. The resulting 1-arseno-3-phosphoglycerate hydrolyses spontaneously, so phos…
- Glycolysis: pyruvate kinase deficiency · Multi-stepA 3-year-old with chronic Coombs-negative haemolytic anaemia has splenomegaly and a blood film showing echinocytes. G6PD activity is normal. Despite a haemoglobin of 7…
- Glycolysis: arsenate poisoning · Multi-stepA farm worker accidentally ingests a pesticide containing sodium arsenate. Red cell glycolysis is studied in vitro. Arsenate substitutes for inorganic phosphate in the…
- Glycolysis · ApplicationWhich enzyme converts phosphoenolpyruvate to pyruvate?
- Glycolysis · ApplicationWhich tissue relies entirely on anaerobic glycolysis?
- Glycolysis · ApplicationWhat enzyme phosphorylates glucose in liver?
Minerals8
- Minerals: hereditary haemochromatosis · ApplicationA 45-year-old man has bronze skin pigmentation, diabetes mellitus, arthropathy of the second and third metacarpophalangeal joints and hepatomegaly. Transferrin saturati…
- Minerals: iron deficiency indices · ApplicationA 14-year-old vegetarian girl with heavy menstrual periods has pallor and koilonychia. Hb is 8 g/dL, MCV 68 fL and RDW is raised. Which laboratory change best reflects…
- Minerals: zinc deficiency · ApplicationA 5-month-old weaned from breast milk develops a perioral and perianal vesiculobullous rash, diarrhoea and hair loss. A mutation in SLC39A4 is found. Which serum enzyme…
- Minerals: Menkes disease · ApplicationA 4-month-old boy has sparse, kinky, steel-coloured hair, seizures, hypotonia, tortuous arteries and metaphyseal spurring. Serum copper and ceruloplasmin are low. Defic…
- Minerals: corrected calcium · Multi-stepA 30-year-old woman with nephrotic syndrome has no tetany. Serum total calcium is 7.2 mg/dL and albumin is 2.0 g/dL. Using the correction of 0.8 mg/dL of calcium for ev…
- Minerals: magnesium and calcium · Multi-stepA 55-year-old man with chronic alcohol use and long-term proton pump inhibitor therapy has persistent hypocalcaemia (serum calcium 6.8 mg/dL) and hypokalaemia despite c…
- Minerals: fluoride excess · ApplicationA village with borewell water containing 4 mg/L fluoride has residents with brown mottled teeth, back stiffness and genu valgum in adolescents. What is the best explana…
- Minerals: molybdenum · Multi-stepA neonate has intractable seizures, lens dislocation and very low serum uric acid. Urine contains high sulfite and S-sulfocysteine. A defect in synthesis of molybdenum…
Urea cycle8
- Urea cycle · ApplicationWhich enzyme catalyses the rate-limiting step of the urea cycle?
- Urea cycle: carbamoyl phosphate synthetase I · Multi-stepA 3-day-old term infant is lethargic and feeds poorly, with a plasma ammonia several times normal. Plasma citrulline and arginine are low, urinary orotic acid is low, a…
- Urea cycle: carbamoyl phosphate synthetase I · ApplicationN-acetylglutamate is made in liver mitochondria when arginine and glutamate are plentiful. It acts as an obligatory allosteric activator of which urea cycle enzyme?
- Urea cycle: carbamoyl phosphate synthetase I · Multi-stepA child on valproate for epilepsy becomes drowsy and vomits, with high ammonia and normal liver enzymes. A valproate metabolite reduces production of N-acetylglutamate.…
- Urea cycle · ApplicationWhich deficiency commonly causes hyperammonemia with low BUN?
- Urea cycle · ApplicationWhich amino acid carries nitrogen to liver from muscle?
- Urea cycle · ApplicationWhat is toxic when elevated in urea-cycle defects?
- Urea cycle: ornithine transcarbamylase · Multi-stepA newborn boy has hyperammonaemia, low blood urea nitrogen and elevated urinary orotic acid without megaloblastic anaemia. Which defect is most likely?
Glycogen storage disorders7
- Glycogen storage disorders · ApplicationVon Gierke disease (glycogen storage disease type I) is due to deficiency of which enzyme?
- Glycogen storage disorders · ApplicationA 20-year-old man has painful cramps and fatigue within minutes of starting vigorous exercise, and dark urine afterwards. During an ischaemic forearm exercise test his…
- Glycogen storage disorders: Pompe disease · ApplicationA 4-month-old infant is hypotonic with feeding difficulty, macroglossia, a markedly enlarged heart and a short PR interval on ECG. Blood glucose is normal. Which enzyme…
- Glycogen storage disorders: Cori disease · Multi-stepA 3-year-old child has hepatomegaly and fasting hypoglycaemia with ketosis. Lactate and uric acid are normal. Transaminases and creatine kinase are raised, and liver bi…
- Glycogen storage disorders: Andersen disease · ApplicationAn infant with failure to thrive develops hepatosplenomegaly and progressive cirrhosis with portal hypertension. Liver biopsy shows PAS-positive, diastase-resistant mat…
- Glycogen storage disorders: Cori disease · Multi-stepA 2-year-old boy has hepatomegaly, fasting hypoglycaemia and ketosis, with raised transaminases and creatine kinase. His plasma lactate and uric acid are normal, and a…
- Glycogen storage disorders: glycogen synthase deficiency · Multi-stepA 3-year-old child has early-morning drowsiness and seizures with hypoglycaemia and ketosis after an overnight fast. After a carbohydrate meal, blood glucose rises exce…
Lipids7
- Lipids: pulmonary surfactant · ApplicationA diabetic mother at 34 weeks has amniocentesis showing a lecithin to sphingomyelin ratio of 1.2. What is the correct interpretation?
- Lipids: essential fatty acids · ApplicationA 5-month-old infant on prolonged fat-free parenteral nutrition develops scaly dermatitis, sparse hair and thrombocytopenia. Which nutrient is lacking?
- Lipids: membrane phospholipids and signalling · ApplicationActivation of a Gq-coupled receptor stimulates phospholipase C, which hydrolyses a membrane phospholipid. Which pair of second messengers is generated?
- Lipids · ApplicationWhere does beta-oxidation occur?
- Lipids · ApplicationWhich enzyme releases fatty acids from triglyceride stores?
- Lipids · ApplicationWhat is main storage form of fat?
- Lipids · ApplicationWhat carries endogenous triglyceride from liver?
Clinical enzymology6
- Clinical enzymology · ApplicationA patient has a raised serum alkaline phosphatase. Which additional finding best indicates a hepatobiliary rather than bone source?
- Clinical enzymology: cardiac markers · Multi-stepA 60-year-old man had an anterior myocardial infarction 4 days ago and now has recurrent chest pain. Troponin I is still elevated from the index event. Which convention…
- Clinical enzymology: transaminases · ApplicationA 45-year-old man with long-term heavy alcohol use has jaundice and tender hepatomegaly. AST is 220 IU/L and ALT 90 IU/L. Which interpretation is best?
- Clinical enzymology: plasma cholinesterase · Multi-stepA 30-year-old man has 3 hours of apnoea after suxamethonium for an appendicectomy. His brother had a similar episode. Which statement best explains the event?
- Clinical enzymology: LDH isoenzymes · ApplicationA 58-year-old man presents 3 days after an episode of prolonged chest pain. Electrophoresis of serum lactate dehydrogenase is requested. Which pattern supports a recent…
- Clinical enzymology: alkaline phosphatase · ApplicationA patient with obstructive jaundice has markedly elevated alkaline phosphatase. Which additional enzyme supports a hepatobiliary rather than bone source?
DNA repair6
- DNA repair · ApplicationSpontaneous deamination of cytosine produces uracil in DNA. Which enzyme initiates the repair of this lesion?
- DNA repair · ApplicationA 35-year-old man has early-onset colorectal cancer with a strong family history and microsatellite instability. Which DNA repair pathway is defective?
- DNA repair: BRCA and PARP inhibitors · Multi-stepA 52-year-old woman with high-grade serous ovarian cancer carrying a germline BRCA1 mutation is treated with olaparib. Which principle explains why the drug is selectiv…
- DNA repair: Fanconi anaemia · Multi-stepA 5-year-old boy has short stature, café-au-lait macules, hypoplastic thumbs and a progressive pancytopenia. Which laboratory result would best confirm the diagnosis an…
- DNA repair: Cockayne syndrome · Multi-stepA 4-year-old has growth failure, microcephaly, sensorineural deafness, retinopathy and severe sunburn on minimal exposure, but there are no skin cancers. Cultured cells…
- DNA repair · ApplicationMismatch repair defects increase risk of what syndrome?
Enzyme kinetics6
- Enzyme kinetics · ApplicationWhich pattern describes a competitive inhibitor?
- Enzyme kinetics: Michaelis-Menten calculation · Multi-stepAn enzyme has a Vmax of 100 micromol per minute and a Km of 2 mM. What is the initial velocity at a substrate concentration of 0.5 mM?
- Enzyme kinetics: inhibition types · Multi-stepIn a Lineweaver-Burk plot, an enzyme without inhibitor has Km 5 mM and Vmax 100. With an inhibitor, the line has double the y-intercept but the same x-intercept. Which…
- Enzyme kinetics: glucokinase · Multi-stepA 14-year-old girl has stable mild fasting hyperglycaemia of about 7 mmol/L with HbA1c 6.4%, no ketosis and a similar finding in her mother. Heterozygous glucokinase mu…
- Enzyme kinetics · ApplicationWhat happens to the apparent Km of an enzyme when a reversible competitive inhibitor is added?
- Enzyme kinetics · ApplicationWhich kinetic change is expected with a pure noncompetitive inhibitor?
Gluconeogenesis6
- Gluconeogenesis: substrates · ApplicationDuring prolonged starvation, which of the following cannot contribute to a net synthesis of glucose in humans?
- Gluconeogenesis: fructose-1,6-bisphosphatase deficiency · ApplicationA 9-month-old develops hypoglycaemia, lactic acidosis, ketosis and hepatomegaly during a febrile illness with poor feeding. Symptoms are worse after fructose or sucrose…
- Gluconeogenesis: glucogenic substrates · Multi-stepA researcher incubates hepatocytes from a fasted rat with different labelled substrates and measures net synthesis of glucose. Which substrate cannot give a net gain of…
- Gluconeogenesis · ApplicationWhich enzyme bypasses pyruvate kinase during gluconeogenesis?
- Gluconeogenesis · ApplicationWhich organ performs most gluconeogenesis?
- Gluconeogenesis · ApplicationWhat substrate can become glucose?
Translation6
- Translation: chloramphenicol and the 50S subunit · ApplicationA premature neonate treated with chloramphenicol for sepsis develops abdominal distension, vomiting, ashen-grey colour and circulatory collapse. At the ribosomal level,…
- Translation: diphtheria toxin · ApplicationA 6-year-old unvaccinated child has fever, a grey adherent tonsillar pseudomembrane, bull neck and myocarditis. The toxin responsible acts by inactivating which target?
- Translation: aminoglycosides · ApplicationA patient with an intra-abdominal abscess containing Bacteroides fragilis shows no response to gentamicin alone. What is the biochemical reason?
- Translation: aminoacyl-tRNA synthetase · Multi-stepAn enzyme sometimes activates a similar smaller amino acid (valine instead of isoleucine) but then hydrolyses the wrong product at a separate editing site before it eve…
- Translation: aminoacyl-tRNA synthetase · ApplicationA topical antibiotic used to clear nasal carriage of MRSA inhibits the bacterial enzyme that loads isoleucine onto its transfer RNA. Which enzyme class is the target?
- Translation: aminoacyl-tRNA synthetase · ApplicationActivating each amino acid for protein synthesis costs the equivalent of two high-energy phosphate bonds, because ATP is cleaved to AMP and pyrophosphate, which is then…
Collagen5
- Collagen: basement membrane defects · ApplicationA 12-year-old boy has haematuria, high-frequency sensorineural hearing loss and anterior lenticonus. His maternal uncle died of renal failure. Which protein is abnormal?
- Collagen: cross-linking and copper · ApplicationA male infant has hypotonia, seizures, sparse kinky hair and tortuous arteries, with low serum copper and ceruloplasmin. Which enzymatic defect explains the connective…
- Collagen: Ehlers-Danlos syndrome · ApplicationA 28-year-old woman has thin translucent skin with visible veins, easy bruising and a spontaneous sigmoid colon perforation. Her brother died of a ruptured aneurysm at…
- Collagen · ApplicationWhich amino acid abnormality is characteristic of collagen?
- Collagen · ApplicationWhich vitamin is required for collagen hydroxylation?
Fatty acid oxidation5
- Fatty acid oxidation: Refsum disease · ApplicationA 30-year-old man has night blindness from retinitis pigmentosa, peripheral neuropathy, cerebellar ataxia, sensorineural deafness and dry scaly skin. Serum phytanic aci…
- Fatty acid oxidation: odd-chain fatty acids · ApplicationThe final round of beta-oxidation of an odd-chain fatty acid yields propionyl-CoA, which is converted to succinyl-CoA. Which cofactors are needed, in order of the react…
- Fatty acid oxidation: stoichiometry · Multi-stepStearic acid (18 carbons) is completely oxidised by mitochondrial beta-oxidation. How many cycles occur, and how many acetyl-CoA, NADH and FADH2 are produced?
- Fatty acid oxidation: carnitine palmitoyltransferase II deficiency · Multi-stepA 19-year-old man has severe muscle pain and dark urine after a long run following an overnight fast and a viral illness. CK is 25,000 U/L. In the ischaemic forearm tes…
- Fatty acid oxidation: toxic hypoglycaemic syndrome · ApplicationAfter eating unripe ackee fruit, a child develops repeated vomiting followed by severe hypoglycaemia with no urinary ketones. Which mechanism best explains the hypoglyc…
Haemoglobin5
- Haemoglobin: structure and mutations · ApplicationIn sickle cell disease the substitution of valine for glutamate at position 6 of the beta chain promotes polymerisation of deoxyhaemoglobin. What type of mutation is th…
- Haemoglobin: oxygen affinity · ApplicationFetal haemoglobin has a higher oxygen affinity than adult haemoglobin at the same 2,3-bisphosphoglycerate concentration. What is the molecular reason?
- Haemoglobin: methaemoglobinaemia · ApplicationA 3-month-old bottle-fed infant given milk prepared with well water becomes cyanosed with SpO2 of 85% that does not improve with oxygen. Blood is chocolate brown. What…
- Haemoglobin: 2,3-BPG in stored blood · ApplicationA patient receives several units of red cells stored for 3 weeks in citrate-phosphate-dextrose. Immediately after transfusion the transfused cells deliver oxygen poorly…
- Haemoglobin · ApplicationWhich physiological change shifts the oxyhaemoglobin dissociation curve to the right?
Nutrition5
- Nutrition: kwashiorkor · ApplicationA 2-year-old is weaned to a starchy gruel after the birth of a sibling. He has pitting pedal oedema, flaky skin, sparse reddish hair and a distended abdomen. What is th…
- Nutrition: protein quality · Multi-stepIn a balance study a subject ingests 10 g of nitrogen, loses 2 g in faeces and 3 g in urine, ignoring endogenous losses. What are the biological value (BV) and net prot…
- Nutrition: respiratory quotient · ApplicationIn a metabolic study, a fasting subject consumes 300 mL of oxygen per minute and produces 210 mL of carbon dioxide per minute. Which fuel is being oxidised predominantly?
- Nutrition · ApplicationWhat does a positive nitrogen balance usually indicate?
- Nutrition: essential fatty acids · ApplicationWhich fatty acid is essential in the human diet because it cannot be synthesized de novo?
TCA cycle5
- TCA cycle: energy yield · Multi-stepUsing P/O ratios of 2.5 for NADH and 1.5 for FADH2, how many ATP equivalents are generated by oxidation of one acetyl-CoA in the TCA cycle?
- TCA cycle: calcium and regulation · ApplicationDuring vigorous muscle contraction, mitochondrial calcium rises and TCA cycle flux increases. Which pair of enzymes is activated by calcium and inhibited by NADH?
- TCA cycle · ApplicationWhich molecule enters TCA cycle by combining with oxaloacetate?
- TCA cycle · ApplicationWhich enzyme of the TCA cycle is directly inhibited by fluoroacetate toxicity through formation of fluorocitrate?
- TCA cycle: anaplerosis · ApplicationWhich reaction replenishes oxaloacetate for the TCA cycle during gluconeogenesis?
Vitamin metabolism5
- Vitamin metabolism · ApplicationWhich laboratory abnormality is specifically associated with vitamin B12 deficiency rather than isolated folate deficiency?
- Vitamin metabolism · ApplicationWhich biochemical process is impaired when folate is deficient?
- Vitamin metabolism · ApplicationDeficiency of which vitamin impairs hydroxylation steps needed for stable collagen cross-linking?
- Vitamin metabolism · ApplicationWhich action is promoted by active vitamin D in calcium homeostasis?
- Vitamin metabolism · ApplicationVitamin K is necessary for gamma-carboxylation of which group of coagulation factors?
Acid-base biochemistry4
- Acid-base biochemistry · ApplicationWhich buffer system is most important in extracellular blood plasma?
- Acid-base biochemistry · ApplicationWhat primary disturbance is present when arterial pH is low and bicarbonate is low?
- Acid-base biochemistry: anion gap · ApplicationWhich acid-base disorder typically produces a high anion gap metabolic acidosis?
- Acid-base biochemistry: anion gap · ApplicationHow is the plasma anion gap commonly calculated?
Bioenergetics4
- Bioenergetics: NADH shuttles · Multi-stepCytosolic NADH from glycolysis of one glucose molecule enters mitochondria through the malate-aspartate shuttle in heart and through the glycerol-3-phosphate shuttle in…
- Bioenergetics: brown adipose tissue · ApplicationNewborns maintain body temperature partly by non-shivering thermogenesis in brown adipose tissue. Which mechanism produces heat in these cells?
- Bioenergetics · ApplicationWhere is most ATP generated during aerobic cellular respiration?
- Bioenergetics · ApplicationCyanide toxicity causes cellular hypoxia by inhibiting which part of the electron transport chain?
Energy metabolism4
- Energy metabolism · ApplicationWhat is the principal immediate cellular energy currency?
- Energy metabolism · ApplicationWhich process generates most ATP during aerobic metabolism?
- Energy metabolism · ApplicationWhere does the citric acid cycle occur in eukaryotic cells?
- Energy metabolism · ApplicationWhat directly powers ATP synthase in oxidative phosphorylation?
Enzyme inhibition4
- Enzyme inhibition: methanol poisoning · ApplicationA 30-year-old man develops blurred vision and a high anion gap metabolic acidosis after drinking adulterated country liquor containing methanol. Fomepizole is given. Ho…
- Enzyme inhibition: organophosphate poisoning · ApplicationA farmer after spraying a pesticide has miosis, salivation, bradycardia and fasciculations, and red cell cholinesterase is low. What is the mechanism of enzyme inhibiti…
- Enzyme inhibition: irreversible inhibition by aspirin · ApplicationA man takes aspirin 75 mg daily. A bleeding time measured three days after he stops aspirin is still prolonged, although aspirin has a plasma half-life of only about 20…
- Enzyme inhibition: trivalent arsenic and lipoamide · Multi-stepA farmer is brought after accidentally ingesting an arsenite-containing pesticide. He has vomiting, a garlic odour on his breath, hypotension and lactic acidosis, with…
Haem synthesis4
- Haem synthesis: delta-aminolevulinate synthase · Multi-stepA man on antituberculous therapy develops a microcytic hypochromic anaemia with ring sideroblasts in the marrow. Isoniazid has depleted a vitamin, impairing the first e…
- Haem synthesis: delta-aminolevulinate synthase · Multi-stepA 20-year-old man has a hypochromic microcytic anaemia with ring sideroblasts, iron overload and a maternal uncle with the same condition. His haemoglobin improves with…
- Haem synthesis: delta-aminolevulinate synthase · ApplicationDuring an acute porphyric attack, intravenous hemin and a high-carbohydrate load are given. Hemin helps by repressing which hepatic enzyme?
- Haem synthesis: delta-aminolevulinate synthase · Multi-stepA woman with acute intermittent porphyria takes phenobarbital for epilepsy and develops severe abdominal pain, psychosis and port-wine urine. Induction of which hepatic…
Laboratory biochemistry4
- Laboratory biochemistry · ApplicationWhich biomarker is most specific for myocardial injury in acute coronary syndrome?
- Laboratory biochemistry · ApplicationWhat does glycated haemoglobin primarily reflect?
- Laboratory biochemistry · ApplicationWhat does an isolated high unconjugated bilirubin suggest in haemolysis?
- Laboratory biochemistry · ApplicationWhich biomarker rises earliest after acute pancreatitis begins?
Nucleotide drugs4
- Nucleotide drugs: mycophenolate · ApplicationA renal transplant recipient is given mycophenolate mofetil. Which mechanism explains its immunosuppressive effect?
- Nucleotide drugs: methotrexate rescue · ApplicationA patient on weekly methotrexate for rheumatoid arthritis presents with mouth ulcers, macrocytosis and neutropenia after a dosing error. Which agent best rescues normal…
- Nucleotide drugs: fluorouracil · Multi-stepA patient with colorectal cancer receives fluorouracil. The active metabolite FdUMP forms a covalent complex with thymidylate synthase. Which intracellular change is ex…
- Nucleotide drugs: cytarabine · ApplicationA 35-year-old with acute myeloid leukaemia receives cytarabine in induction chemotherapy. Which statement best describes its action?
Pentose phosphate pathway4
- Pentose phosphate pathway · ApplicationAn 8-year-old boy develops dark urine and jaundice two days after eating fava beans. Blood film shows Heinz bodies and bite cells. What is the primary biochemical defec…
- Pentose phosphate pathway: G6PD · Multi-stepA man develops jaundice and dark urine after receiving primaquine. Which product of the pentose phosphate pathway is deficient in his red cells?
- Pentose phosphate pathway · ApplicationWhat is the principal product of the oxidative phase of the pentose phosphate pathway that protects red cells from oxidant injury?
- Pentose phosphate pathway: transketolase · ApplicationWhy is erythrocyte transketolase activity used in suspected thiamine deficiency?
Purine catabolism4
- Purine catabolism: drug interaction · Multi-stepA man with gout is on allopurinol. Azathioprine is started at its usual dose after a renal transplant, and he develops pancytopenia within 3 weeks. What is the explanat…
- Purine catabolism: tumour lysis syndrome · Multi-stepA 10-year-old boy with Burkitt lymphoma has high uric acid and is about to receive chemotherapy. Rasburicase is planned. Which test must be done first, and why?
- Purine catabolism: xanthinuria · ApplicationA 30-year-old man has recurrent renal stones. Serum uric acid is very low at 0.5 mg/dL, and the urine contains high levels of xanthine and hypoxanthine. Which enzyme is…
- Purine catabolism: purine nucleoside phosphorylase deficiency · Multi-stepA 2-year-old boy has recurrent opportunistic infections, lymphopenia and neurological delay. Serum uric acid is 0.4 mg/dL, and an enzyme assay shows absent purine nucle…
Purine salvage4
- Purine salvage: APRT deficiency · ApplicationA 6-year-old boy has recurrent radiolucent renal stones and haematuria. Serum uric acid is normal and there are no neurological problems. Urine microscopy shows round b…
- Purine salvage: hypoxanthine-guanine phosphoribosyltransferase · Multi-stepFibroblasts from a boy with urate overproduction show a markedly raised intracellular PRPP concentration and an increased rate of de novo purine synthesis. Which enzyme…
- Purine salvage: hypoxanthine-guanine phosphoribosyltransferase · Multi-stepA boy with severe gout and renal stones is treated with allopurinol and his urate falls to normal. Dystonia, intellectual disability and self-injury continue. Which enz…
- Purine salvage: hypoxanthine-guanine phosphoribosyltransferase · Multi-stepA 22-year-old man with normal intelligence develops early gout and uric acid stones. Enzyme assay shows a small residual activity of the same salvage enzyme that is abs…
Pyrimidine synthesis4
- Pyrimidine synthesis: orotic aciduria · ApplicationAn 8-month-old infant has failure to thrive and megaloblastic anaemia that does not respond to vitamin B12 or folate. Urine contains orotic acid crystals and ammonia is…
- Pyrimidine synthesis: leflunomide · ApplicationA woman with rheumatoid arthritis takes leflunomide. Its active metabolite, teriflunomide, preferentially suppresses activated lymphocytes because it inhibits which enz…
- Pyrimidine synthesis: carbamoyl phosphate synthetase II · ApplicationA student compares the two carbamoyl phosphate synthetases. Which statement correctly describes carbamoyl phosphate synthetase II?
- Pyrimidine synthesis: orotate phosphoribosyltransferase · ApplicationIn the de novo pyrimidine pathway, which enzyme transfers a ribose phosphate from PRPP to the ring after it has been built, forming the first nucleotide of the pathway?
Acid-base3
- Acid-base: anion gap and urine anion gap · Multi-stepA 6-year-old has had 3 days of watery diarrhoea. Serum sodium is 134, chloride 112 and bicarbonate 12 mmol/L. What are the serum anion gap and the expected urine anion…
- Acid-base: compensation in metabolic acidosis · Multi-stepA 20-year-old with diabetic ketoacidosis has been vomiting and is becoming drowsy. Arterial blood gas shows pH 7.10, bicarbonate 12 mmol/L and PaCO2 40 mmHg. Using Wint…
- Acid-base · ApplicationWhat is the main renal response to chronic respiratory acidosis?
Acid-base chemistry3
- Acid-base chemistry · ApplicationA patient has plasma bicarbonate of 24 mmol/L and PaCO2 of 80 mmHg. Take pKa as 6.1, CO2 solubility as 0.03 mmol/L per mmHg, and log 10 = 1. What is the approximate pH?
- Acid-base chemistry: buffer calculation · Multi-stepOne litre of a phosphate buffer contains 0.10 mol of HPO4(2-) and 0.01 mol of H2PO4(-); the pKa of the pair is 6.8. Then 0.005 mol of HCl is added and mixed without vol…
- Acid-base chemistry · ApplicationWhat is the most important extracellular buffer system in human blood?
Carbohydrate digestion3
- Carbohydrate digestion: lactase deficiency · ApplicationA 24-year-old woman has bloating, cramps and watery diarrhoea within an hour of drinking milk, relieved by avoiding dairy. Which stool finding is expected during an att…
- Carbohydrate digestion: lactase deficiency · ApplicationA 9-month-old infant recovering from rotavirus gastroenteritis develops explosive watery stools, perianal excoriation and abdominal distension after restarting formula…
- Carbohydrate digestion: sucrase-isomaltase deficiency · Multi-stepA 2-year-old has watery diarrhoea and bloating after sweets and table sugar, but tolerates milk. Stool is negative for reducing substances until it is boiled with dilut…
Collagen synthesis3
- Collagen synthesis: vitamin C · Multi-stepA water-soluble vitamin is a cofactor for the copper enzyme that converts dopamine to norepinephrine in chromaffin granules. It also keeps the iron of collagen-modifyin…
- Collagen synthesis: scurvy · ApplicationPoor wound healing and perifollicular haemorrhages in scurvy arise because vitamin C is needed for hydroxylation of which residues in collagen?
- Collagen synthesis · ApplicationWhich vitamin is required for hydroxylation of proline and lysine during collagen synthesis?
Electrolytes3
- Electrolytes: SIADH · Multi-stepA 62-year-old smoker with small cell lung carcinoma is euvolaemic with serum sodium 120 mmol/L and serum osmolality 255 mOsm/kg. Which urine findings confirm SIADH?
- Electrolytes: pseudohyponatraemia · Multi-stepA patient with uncontrolled familial hypertriglyceridaemia has milky serum and a sodium of 124 mmol/L by indirect ion-selective electrode. Measured osmolality is 290 mO…
- Electrolytes: hypokalaemia · ApplicationA 35-year-old woman with persistent vomiting has serum potassium of 2.6 mmol/L and metabolic alkalosis. Which ECG changes are most likely?
Fatty acid synthesis3
- Fatty acid synthesis: source of NADPH · ApplicationHepatic fatty acid synthesis requires large amounts of cytosolic NADPH. Which pair of reactions is the main source?
- Fatty acid synthesis: acetyl-CoA carboxylase · Multi-stepDuring prolonged exercise, AMP-activated protein kinase phosphorylates and inhibits a biotin-dependent enzyme of fatty acid synthesis. This lowers the level of the prod…
- Fatty acid synthesis: acetyl-CoA carboxylase · ApplicationA cytosolic liver enzyme assembles into long active filaments in the presence of citrate and breaks into inactive protomers when long-chain acyl-CoA accumulates. Which…
Glycogen metabolism3
- Glycogen metabolism: glycogen phosphorylase · Multi-stepA 3-year-old boy has hepatomegaly, growth retardation and mild fasting hypoglycaemia with mild ketosis. Lactate and uric acid are normal, and the storage polymer in the…
- Glycogen metabolism: McArdle disease · ApplicationA teenager has painful cramps with brief intense exercise, myoglobinuria, and a normal rise in lactate is absent after exercise. Which enzyme is deficient?
- Glycogen metabolism: glycogenolysis · ApplicationWhich enzyme releases glucose-1-phosphate from the nonreducing ends of glycogen during glycogenolysis?
Glycogen storage disease3
- Glycogen storage disease: von Gierke · ApplicationAn infant has severe fasting hypoglycemia, hepatomegaly, lactic acidosis, hyperuricemia, and hypertriglyceridemia. Which enzyme deficiency is most likely?
- Glycogen storage disease: Pompe · ApplicationAn infant has hypotonia, macroglossia, hypertrophic cardiomyopathy, and elevated CK. Which enzyme is deficient?
- Glycogen storage disease: McArdle · ApplicationA young adult has exercise intolerance, muscle cramps, myoglobinuria, and no rise in serum lactate after ischemic exercise testing. What deficiency is likely?
Heme3
Hormones3
Lysosomal storage disorders3
- Lysosomal storage disorders · ApplicationA child has hepatosplenomegaly, anaemia, thrombocytopenia and bone pain. A marrow aspirate shows macrophages with crumpled tissue-paper cytoplasm. Which substance is ac…
- Lysosomal storage disorders · ApplicationAn 8-month-old infant has regression of milestones, exaggerated startle to sound, hypotonia and a cherry-red macular spot, with no hepatosplenomegaly or coarse facial f…
- Lysosomal storage disorders · ApplicationA 12-year-old boy has burning pain in the hands and feet, dark red spots on the skin of the trunk and proteinuria. His maternal uncle died of renal failure. Which enzym…
Metabolism3
- Metabolism: ethanol · Multi-stepA chronic alcohol drinker is found after a binge without food, with hypoglycaemia and lactic acidosis. What best explains the hypoglycaemia?
- Metabolism: adaptation to starvation · ApplicationA man on a hunger strike has been fasting for 10 days. His urinary nitrogen loss has fallen compared with day 2. What best explains the fall?
- Metabolism · ApplicationWhat rises in fasting?
Molecular techniques3
- Molecular techniques: real-time PCR interpretation · Multi-stepIn a quantitative reverse transcription PCR for HIV-1 RNA, sample A crosses the fluorescence threshold at cycle 20 and sample B at cycle 28. Assuming equal efficiency o…
- Molecular techniques: Sanger sequencing · ApplicationIn a Sanger sequencing reaction, the newly synthesised strand reads 5'-ATGCCG-3' when fragments are ordered from shortest to longest. What is the sequence of the templa…
- Molecular techniques: RFLP in sickle cell disease · Multi-stepIn prenatal diagnosis, fetal DNA is cut with the restriction enzyme MstII and probed for the beta-globin gene. The sickle mutation (GAG to GTG) destroys an MstII site.…
Oxidative stress3
Peroxisomal disorders3
- Peroxisomal disorders · ApplicationA hypotonic neonate has a high forehead, flat facies, hepatomegaly and seizures, with raised very long chain fatty acids in plasma. Which organelle function is deficient?
- Peroxisomal disorders: X-linked adrenoleukodystrophy · Multi-stepAn 8-year-old boy has declining school performance, visual difficulty and skin hyperpigmentation. His morning cortisol is low with a very high ACTH, and MRI shows poste…
- Peroxisomal disorders: Zellweger syndrome · ApplicationA neonate has marked hypotonia, a high forehead, seizures, hepatomegaly and no feeding. Plasma very long chain fatty acids are raised and plasmalogens are low. What is…
Plasma proteins3
- Plasma proteins: acute phase response · ApplicationA man with severe sepsis has interleukin-6 driven changes in hepatic protein synthesis. Which plasma protein is expected to fall?
- Plasma proteins: albumin as a carrier · ApplicationA jaundiced preterm neonate is given a sulfonamide for infection and develops kernicterus at a bilirubin level lower than expected. Which mechanism best explains this?
- Plasma proteins: alpha-1 antitrypsin · ApplicationA young non-smoker has panacinar emphysema predominantly in the lower lobes. Deficiency of which protease inhibitor is likely?
Purines3
RNA processing3
- RNA processing: spliceosome and anti-Sm antibody · ApplicationA 24-year-old woman has a malar rash, arthritis, proteinuria and positive antinuclear antibodies. Anti-Sm antibodies are present, a highly specific marker for her disea…
- RNA processing: 5-prime cap · ApplicationA laboratory transcribes an mRNA in vitro for expression in human cells, but without any 5-prime modification. The mRNA is degraded quickly and translated poorly. Which…
- RNA processing: splicing · ApplicationWhich RNA-processing complex removes introns from eukaryotic pre-mRNA and joins the remaining exons?
Sphingolipidoses3
- Sphingolipidoses: Niemann-Pick disease · ApplicationA 10-month-old infant has hepatosplenomegaly, feeding difficulty, progressive hypotonia and a cherry-red spot on the macula. A bone marrow aspirate shows foamy lipid-la…
- Sphingolipidoses: Krabbe disease · ApplicationA 5-month-old infant is irritable, with episodes of unexplained crying, spasticity, loss of head control, optic atrophy and peripheral neuropathy. MRI shows demyelinati…
- Sphingolipidoses: metachromatic leukodystrophy · ApplicationA 2-year-old who was previously normal develops a clumsy gait, loss of speech and a peripheral neuropathy with slowed nerve conduction. MRI shows symmetrical periventri…
Thyroid hormone synthesis3
- Thyroid hormone synthesis: thyroid peroxidase · ApplicationA woman with Graves disease is started on carbimazole. Inside the follicular cell, the drug mainly prevents iodide oxidation, iodination and coupling by inhibiting whic…
- Thyroid hormone synthesis: thyroid peroxidase · Multi-stepA neonate has a goitre, high TSH and low T4. A radioiodine uptake study is high, and giving perchlorate releases most of the trapped iodine from the gland. Which enzyme…
- Thyroid hormone synthesis: thyroid peroxidase · ApplicationA woman with a firm goitre has lymphocytic infiltration and Hurthle cells on biopsy. Her serum contains autoantibodies once called antimicrosomal. Which enzyme do they…
Transcription3
- Transcription: RNA polymerase II inhibition · ApplicationA family in a hill district eats wild mushrooms and, after 8 hours of vomiting and watery diarrhoea, one member improves briefly and then develops jaundice and hepatic…
- Transcription: RNA polymerase II · ApplicationThe largest subunit of a nuclear enzyme carries a carboxy-terminal domain of repeated heptapeptides whose phosphorylation coordinates capping, splicing and polyadenylat…
- Transcription: RNA polymerase II · ApplicationAt a protein-coding gene, TBP within TFIID binds the TATA box. TFIIB and TFIIF then bring in which enzyme to complete the preinitiation complex?
Tumour markers3
- Tumour markers: testicular germ cell tumours · ApplicationA 25-year-old man has a testicular mass. Serum AFP is 800 ng/mL and beta-hCG is mildly raised. The orchidectomy specimen is reported as classical seminoma only. How sho…
- Tumour markers: CA-125 · ApplicationA 58-year-old postmenopausal woman has a complex adnexal mass and ascites, with serum CA-125 of 850 U/mL. After surgery for serous epithelial ovarian carcinoma and chem…
- Tumour markers: free PSA · Multi-stepA 66-year-old man has a total PSA of 7 ng/mL with a normal rectal examination. The free to total PSA ratio is 8%. How is this interpreted?
Amino acid transport2
- Amino acid transport: Hartnup disease · ApplicationAn 8-year-old boy has episodic photosensitive pellagra-like rash, intermittent cerebellar ataxia and emotional lability, which are triggered by poor diet and illness. S…
- Amino acid transport: cystinosis · Multi-stepAn 8-month-old infant has polyuria, polydipsia, failure to thrive and rickets with a normal anion gap acidosis, glycosuria with normal blood glucose, phosphaturia and a…
Amino acid transport disorders2
- Amino acid transport disorders · ApplicationA 28-year-old man has recurrent flank pain with hexagonal crystals in the urine. The sodium nitroprusside test is positive. Which amino acids are excreted in excess?
- Amino acid transport disorders: Hartnup disease · ApplicationA 9-year-old boy has episodes of a photosensitive pellagra-like rash and intermittent cerebellar ataxia. Urine shows excess neutral amino acids such as alanine and glut…
Amino-acid metabolism2
Bilirubin metabolism2
- Bilirubin metabolism · ApplicationA young man has mild intermittent unconjugated hyperbilirubinaemia after fasting and during illness, with normal liver enzymes and no haemolysis. What is the underlying…
- Bilirubin metabolism: Dubin-Johnson syndrome · Multi-stepA 20-year-old man has mild recurrent jaundice with conjugated hyperbilirubinaemia, normal ALT and ALP and a good prognosis. A liver biopsy done for another reason shows…
Biotransformation2
Carbohydrates2
Cell signaling2
Collagen disorders2
- Collagen disorders: osteogenesis imperfecta · ApplicationA newborn has multiple intrauterine fractures, blue sclerae and deformed long bones. Sequencing shows a heterozygous COL1A1 variant replacing a glycine in a Gly-X-Y rep…
- Collagen disorders · ApplicationA child has hyperextensible skin, joint hypermobility, and easy bruising due to defective collagen processing. What disorder is most likely?
DNA2
Enzymology2
Free radicals2
- Free radicals: vitamin E in membranes · ApplicationA premature infant on high oxygen therapy has haemolytic anaemia and a low serum tocopherol level. How does vitamin E protect red cell membranes?
- Free radicals: superoxide dismutase · ApplicationA 45-year-old man has progressive limb weakness with both upper and lower motor neuron signs, and a family history of similar illness. Genetic testing finds a mutation…
Glycogen2
Glycogen storage2
Glycoproteins2
- Glycoproteins: blood group biochemistry · Multi-stepA woman whose red cells type as group O has serum that agglutinates group O red cells from other donors. Her daughter, fathered by a group A man, is group AB. Which def…
- Glycoproteins: N-linked glycosylation · ApplicationA drug blocks the first step of N-linked glycosylation by inhibiting transfer of N-acetylglucosamine-1-phosphate to dolichol phosphate. Which statement correctly descri…
Haemoglobinopathies2
- Haemoglobinopathies: alpha thalassaemia · ApplicationA stillborn hydropic fetus of a couple of Southeast Asian ancestry has massive hepatosplenomegaly and haemoglobin electrophoresis showing predominantly Hb Bart's. Which…
- Haemoglobinopathies: HbE as a splicing variant · Multi-stepA 7-year-old boy from Assam has moderate microcytic anaemia. Electrophoresis shows HbE and HbF with no HbA; his father has HbE trait and his mother has beta-thalassaemi…
Insulin signalling2
- Insulin signalling: receptor tyrosine kinase · ApplicationA growth factor binds a surface receptor; the receptor dimerises and autophosphorylates, recruits Grb2 and SOS, and switches on the Ras-MAPK cascade. Which receptor cla…
- Insulin signalling: receptor tyrosine kinase · Multi-stepA gastrointestinal stromal tumour carries a gain-of-function mutation in the KIT surface receptor, which dimerises and signals without ligand. Imatinib controls the tum…
Iron metabolism2
- Iron metabolism · Multi-stepA man with long-standing rheumatoid arthritis has anaemia with low serum iron, low transferrin saturation and a raised ferritin. Which mechanism best explains the low s…
- Iron metabolism: hereditary haemochromatosis · Multi-stepA 45-year-old man has skin bronzing, new diabetes, arthropathy of the second and third metacarpophalangeal joints and hepatomegaly. Serum ferritin is 1800 ng/mL and tra…
Laboratory medicine2
Lysosomal storage2
- Lysosomal storage: mucopolysaccharidoses · Multi-stepA 4-year-old boy has coarse facies, hepatosplenomegaly, joint stiffness, aggressive behaviour and hearing loss. Slit-lamp examination shows clear corneas. His maternal…
- Lysosomal storage: Gaucher disease · ApplicationAn 8-year-old boy has splenomegaly, anaemia, thrombocytopenia and bone pain with an Erlenmeyer flask deformity of the femur. Marrow shows macrophages with crumpled tiss…
Mineral metabolism2
- Mineral metabolism · Multi-stepA man with advanced chronic kidney disease has low serum calcium, high phosphate and raised parathyroid hormone. Which biochemical defect most directly lowers his calci…
- Mineral metabolism: hypomagnesaemia and calcium · Multi-stepA 58-year-old woman on long-term proton pump inhibitor and a loop diuretic has tetany. Serum calcium is 7.0 mg/dL, potassium 3.0 mmol/L and PTH is inappropriately low,…
Phospholipids2
- Phospholipids: lung surfactant · ApplicationA neonate born at 30 weeks becomes tachypnoeic with grunting and chest retractions soon after birth. The chest radiograph shows a ground-glass appearance with air bronc…
- Phospholipids: cardiolipin and Barth syndrome · ApplicationAn infant boy has dilated cardiomyopathy, cyclical neutropenia and skeletal myopathy, with 3-methylglutaconic aciduria. The disorder is caused by tafazzin mutation affe…
Protein misfolding2
- Protein misfolding: prion disease · ApplicationA 58-year-old woman has rapidly progressive dementia over 3 months with myoclonus. The EEG shows periodic sharp wave complexes. What is the molecular basis of this dise…
- Protein misfolding: alpha-1 antitrypsin deficiency · Multi-stepA 3-month-old girl has prolonged cholestatic jaundice. Liver biopsy shows PAS-positive, diastase-resistant globules in periportal hepatocytes. Her uncle, a non-smoker,…
Purine synthesis2
- Purine synthesis: origin of ring atoms · ApplicationA researcher traces the origin of atoms in newly synthesised IMP. Carbon 4, carbon 5 and nitrogen 7 of the purine ring come from which compound?
- Purine synthesis: PRPP synthetase superactivity · ApplicationA 22-year-old man has gout, uric acid urolithiasis and sensorineural hearing loss. HGPRT activity is normal, but PRPP synthetase shows increased activity (X-linked). Wh…
Tumour suppressors2
- Tumour suppressors: p53 in Li-Fraumeni syndrome · ApplicationA girl develops an osteosarcoma at 10 years of age. Her mother had breast cancer at 32 and her maternal uncle had a sarcoma at 25. A germline TP53 mutation is identifie…
- Tumour suppressors: retinoblastoma · Multi-stepA 1-year-old has bilateral retinoblastoma, and his father had a unilateral tumour in childhood. Compared with sporadic retinoblastoma, why does the inherited form prese…
Urea cycle disorders2
- Urea cycle disorders · Multi-stepA 3-day-old boy is lethargic with a very high plasma ammonia, low citrulline and high urinary orotic acid. His maternal uncle died in infancy. Which enzyme is deficient?
- Urea cycle disorders: arginase deficiency · ApplicationA 3-year-old child has progressive spastic diplegia, poor growth and occasional mild hyperammonaemic episodes. Plasma arginine is markedly raised. Which enzyme is defic…
Acid-base and electrolytes1
Cyclic nucleotides1
Deoxyribonucleotide synthesis1
Folate metabolism1
Glycogen storage diseases1
Heme synthesis disorders1
Hormonal signaling1
Hormone biochemistry1
Ketone body metabolism1
Mitochondrial inheritance1
Molecular diagnostics1
Nucleic acid structure1
Pentose phosphate1
Protein biochemistry1
Protein degradation1
Purine salvage and degradation1
Reactive oxygen species1
Redox metabolism1
Vitamin B12 metabolism1
Common questions
How many Biochemistry questions are there?
921 original questions across 699 topics, and the bank grows over time.
Which Biochemistry topics are covered?
Nucleotide metabolism, Vitamins, Amino acid metabolism, Glycogen storage diseases, Enzyme kinetics, Glycogen storage disorders, Molecular biology, Urea cycle, Heme synthesis disorders, Lysosomal storage disorders, Pentose phosphate pathway, Ketone body metabolism, and more.
How difficult are these Biochemistry questions?
0 are recall, 678 are application and 243 are multi-step. The tags are our own editorial judgement, not an official difficulty rating.
Are these Biochemistry questions from past papers?
No. They are original practice items. NBEMS does not publish its paper or an official key, and we do not use recalled or leaked questions.
Can I practise Biochemistry for free?
Yes. The free plan includes 20 practice questions a day across all subjects, and a full Biochemistry subject test. A paid term removes the daily limit.
Is there a timed Biochemistry test?
Yes. The Biochemistry subject test is included on the free plan, with a countdown and a question palette.
How should I use these Biochemistry questions?
Answer before you look, read the reason for every option, and write a three-line note for each mistake. A few questions you fully review are worth more than many you skim.
Have these Biochemistry questions been reviewed by faculty?
Not yet. They are original and drafted with AI assistance, then edited by our team. Independent faculty review is planned, and each item shows its status. Confirm important facts in a standard textbook.