Vitamin B12 metabolism: 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 · Vitamin B12 metabolism

Sample item

Which metabolite rises in vitamin B12 deficiency but not isolated folate deficiency?

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

The answer and the reasoning

B. Methylmalonic acid

Vitamin B12 is required for methylmalonyl-CoA mutase, so deficiency raises methylmalonic acid. Both B12 and folate deficiency can raise homocysteine.

Option by option

  • A. Homocysteine only

    Homocysteine can rise in both deficiencies.

  • B. Methylmalonic acid (correct)

    Correct. Methylmalonic acid distinguishes B12 from isolated folate deficiency.

  • C. Uric acid

    Uric acid is not the key discriminating marker.

  • D. Lactate

    Lactate is unrelated to this vitamin distinction.

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 B, Methylmalonic acid. Vitamin B12 is required for methylmalonyl-CoA mutase, so deficiency raises methylmalonic acid.

Why is "Homocysteine only" not the answer?

Homocysteine can rise in both deficiencies.

Why is "Uric acid" not the answer?

Uric acid is not the key discriminating marker.

Why is "Lactate" not the answer?

Lactate is unrelated to this vitamin distinction.

What concept does this question test?

It tests Vitamin B12 metabolism in Biochemistry. Both B12 and folate deficiency can raise homocysteine.

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 Vitamin B12 metabolism?

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.