Carbohydrate metabolism: gluconeogenesis regulation: 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 · Carbohydrate metabolism: gluconeogenesis regulation

Sample item

During prolonged fasting, hepatic beta-oxidation raises mitochondrial acetyl-CoA. Which enzyme is directly activated by acetyl-CoA to favour conversion of pyruvate to oxaloacetate?

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

The answer and the reasoning

D. Pyruvate carboxylase

Pyruvate carboxylase is a biotin-dependent mitochondrial enzyme that is allosterically activated by acetyl-CoA. In fasting, acetyl-CoA from fatty acid oxidation therefore directs pyruvate towards oxaloacetate and gluconeogenesis rather than into the TCA cycle via acetyl-CoA. At the same time acetyl-CoA inhibits pyruvate dehydrogenase.

Option by option

  • A. Glucokinase

    Glucokinase is induced by insulin and is not regulated by acetyl-CoA.

  • B. Pyruvate kinase

    Pyruvate kinase is inhibited by alanine and by glucagon-mediated phosphorylation, not activated by acetyl-CoA.

  • C. Pyruvate dehydrogenase

    Pyruvate dehydrogenase is inhibited by acetyl-CoA and NADH, which spares pyruvate for gluconeogenesis.

  • D. Pyruvate carboxylase (correct)

    Correct. Acetyl-CoA is its specific allosteric activator.

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.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Pyruvate carboxylase. Pyruvate carboxylase is a biotin-dependent mitochondrial enzyme that is allosterically activated by acetyl-CoA.

Why is "Glucokinase" not the answer?

Glucokinase is induced by insulin and is not regulated by acetyl-CoA.

Why is "Pyruvate kinase" not the answer?

Pyruvate kinase is inhibited by alanine and by glucagon-mediated phosphorylation, not activated by acetyl-CoA.

Why is "Pyruvate dehydrogenase" not the answer?

Pyruvate dehydrogenase is inhibited by acetyl-CoA and NADH, which spares pyruvate for gluconeogenesis.

What concept does this question test?

It tests Carbohydrate metabolism: gluconeogenesis regulation in Biochemistry. In fasting, acetyl-CoA from fatty acid oxidation therefore directs pyruvate towards oxaloacetate and gluconeogenesis rather than into the TCA cycle via acetyl-CoA. At the same time acetyl-CoA inhibits pyruvate dehydrogenase.

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 Carbohydrate metabolism: gluconeogenesis regulation?

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.