Vitamins: folate trap: 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 · Vitamins: folate trap

Sample item

In vitamin B12 deficiency, which folate derivative accumulates because methionine synthase cannot regenerate tetrahydrofolate?

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

The answer and the reasoning

B. 5-methyltetrahydrofolate

Cobalamin is required for transfer of the methyl group from 5-methyltetrahydrofolate to homocysteine. Its deficiency traps folate in this form and impairs DNA synthesis.

Option by option

  • A. N5,N10-methylenetetrahydrofolate

    Methylene-THF is used in thymidylate synthesis.

  • B. 5-methyltetrahydrofolate (correct)

    Correct. The methyl-folate trap explains functional folate deficiency in B12 deficiency.

  • C. Tetrahydrofolate

    THF is depleted functionally rather than accumulated.

  • D. Formiminotetrahydrofolate

    Formimino-THF accumulates in some folate-pathway defects.

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 B, 5-methyltetrahydrofolate. Cobalamin is required for transfer of the methyl group from 5-methyltetrahydrofolate to homocysteine.

Why is "N5,N10-methylenetetrahydrofolate" not the answer?

Methylene-THF is used in thymidylate synthesis.

Why is "Tetrahydrofolate" not the answer?

THF is depleted functionally rather than accumulated.

Why is "Formiminotetrahydrofolate" not the answer?

Formimino-THF accumulates in some folate-pathway defects.

What concept does this question test?

It tests Vitamins: folate trap in Biochemistry. Its deficiency traps folate in this form and impairs DNA synthesis.

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 Vitamins: folate trap?

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.