Pentose phosphate pathway: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Pentose phosphate pathway

Sample item

An 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 defect in his red cells?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Inadequate NADPH, so oxidised glutathione cannot be reduced

In G6PD deficiency the pentose phosphate pathway cannot generate enough NADPH. Red cells then cannot regenerate reduced glutathione, so oxidants such as fava beans or primaquine denature haemoglobin into Heinz bodies and cause haemolysis.

Option by option

  • A. Impaired haem synthesis

    Impaired haem synthesis causes sideroblastic anaemia or porphyria and not haemolysis after oxidant exposure.

  • B. Reduced synthesis of beta-globin chains

    Reduced beta-globin synthesis is beta thalassaemia, with microcytic anaemia and no oxidant-triggered attacks.

  • C. Inadequate ATP from glycolysis

    ATP failure from glycolytic enzyme deficiency, as in pyruvate kinase deficiency, causes chronic haemolysis without oxidant triggers.

  • D. Inadequate NADPH, so oxidised glutathione cannot be reduced (correct)

    Correct. Low NADPH leaves red cells unprotected against oxidative stress.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Inadequate NADPH, so oxidised glutathione cannot be reduced. In G6PD deficiency the pentose phosphate pathway cannot generate enough NADPH.

Why is "Impaired haem synthesis" not the answer?

Impaired haem synthesis causes sideroblastic anaemia or porphyria and not haemolysis after oxidant exposure.

Why is "Reduced synthesis of beta-globin chains" not the answer?

Reduced beta-globin synthesis is beta thalassaemia, with microcytic anaemia and no oxidant-triggered attacks.

Why is "Inadequate ATP from glycolysis" not the answer?

ATP failure from glycolytic enzyme deficiency, as in pyruvate kinase deficiency, causes chronic haemolysis without oxidant triggers.

What concept does this question test?

It tests Pentose phosphate pathway in Biochemistry. Red cells then cannot regenerate reduced glutathione, so oxidants such as fava beans or primaquine denature haemoglobin into Heinz bodies and cause haemolysis.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Pentose phosphate pathway?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.