Glycolysis: pyruvate kinase deficiency: 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.

Try it

Biochemistry · Glycolysis: pyruvate kinase deficiency

Sample item

A 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 g/dL, she tolerates activity surprisingly well. Which biochemical change best explains this?

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

The answer and the reasoning

A. Raised red cell 2,3-bisphosphoglycerate shifting the oxygen dissociation curve to the right

Pyruvate kinase deficiency impairs the final ATP-generating step of red cell glycolysis, so cells become rigid and are destroyed in the spleen. Upstream intermediates, including 1,3-bisphosphoglycerate, accumulate and drive the Rapoport-Luebering shunt, raising 2,3-BPG. This right shift lowers oxygen affinity and improves tissue oxygen unloading.

Option by option

  • A. Raised red cell 2,3-bisphosphoglycerate shifting the oxygen dissociation curve to the right (correct)

    Correct. Raised 2,3-BPG lowers haemoglobin oxygen affinity and offsets the anaemia.

  • B. Increased fetal haemoglobin binding oxygen avidly

    Raised fetal haemoglobin does not explain the findings and a left shift would impair oxygen release.

  • C. Raised red cell NADPH that protects against oxidative damage

    NADPH is not raised; reduced NADPH is the problem in G6PD deficiency, which is excluded here.

  • D. Low red cell 2,3-bisphosphoglycerate shifting the oxygen dissociation curve to the left

    Low 2,3-BPG with a left shift occurs in hexokinase deficiency, which would worsen oxygen delivery.

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 A, Raised red cell 2,3-bisphosphoglycerate shifting the oxygen dissociation curve to the right. Pyruvate kinase deficiency impairs the final ATP-generating step of red cell glycolysis, so cells become rigid and are destroyed in the spleen.

Why is "Increased fetal haemoglobin binding oxygen avidly" not the answer?

Raised fetal haemoglobin does not explain the findings and a left shift would impair oxygen release.

Why is "Raised red cell NADPH that protects against oxidative damage" not the answer?

NADPH is not raised; reduced NADPH is the problem in G6PD deficiency, which is excluded here.

Why is "Low red cell 2,3-bisphosphoglycerate shifting the oxygen dissociation…" not the answer?

Low 2,3-BPG with a left shift occurs in hexokinase deficiency, which would worsen oxygen delivery.

What concept does this question test?

It tests Glycolysis: pyruvate kinase deficiency in Biochemistry. Upstream intermediates, including 1,3-bisphosphoglycerate, accumulate and drive the Rapoport-Luebering shunt, raising 2,3-BPG. This right shift lowers oxygen affinity and improves tissue oxygen unloading.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Glycolysis: pyruvate kinase deficiency?

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.