Amino acid metabolism: mixed glucogenic and ketogenic: 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 · Amino acid metabolism: mixed glucogenic and ketogenic

Sample item

Which one of these amino acids gives rise to both glucogenic and ketogenic products during catabolism?

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

The answer and the reasoning

A. Isoleucine

Isoleucine is cleaved to acetyl-CoA, which is ketogenic, and propionyl-CoA, which enters the TCA cycle as succinyl-CoA and is glucogenic. Leucine and lysine are purely ketogenic and valine is purely glucogenic.

Option by option

  • A. Isoleucine (correct)

    Correct. Isoleucine yields acetyl-CoA and propionyl-CoA.

  • B. Lysine

    Lysine also yields only acetyl-CoA derivatives and is purely ketogenic.

  • C. Leucine

    Leucine yields only acetyl-CoA and acetoacetate and is purely ketogenic.

  • D. Valine

    Valine yields propionyl-CoA only and is purely glucogenic.

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 A, Isoleucine. Isoleucine is cleaved to acetyl-CoA, which is ketogenic, and propionyl-CoA, which enters the TCA cycle as succinyl-CoA and is glucogenic.

Why is "Lysine" not the answer?

Lysine also yields only acetyl-CoA derivatives and is purely ketogenic.

Why is "Leucine" not the answer?

Leucine yields only acetyl-CoA and acetoacetate and is purely ketogenic.

Why is "Valine" not the answer?

Valine yields propionyl-CoA only and is purely glucogenic.

What concept does this question test?

It tests Amino acid metabolism: mixed glucogenic and ketogenic in Biochemistry. Leucine and lysine are purely ketogenic and valine is purely glucogenic.

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 Amino acid metabolism: mixed glucogenic and ketogenic?

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.