Nucleotide 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 · Nucleotide metabolism

Sample item

What enzyme is inhibited by methotrexate?

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

The answer and the reasoning

B. Dihydrofolate reductase

Methotrexate inhibits dihydrofolate reductase, reducing tetrahydrofolate regeneration and thereby impairing nucleotide synthesis in rapidly dividing cells.

Option by option

  • A. Thymidylate synthase

    Thymidylate synthase is directly inhibited by 5-fluorouracil.

  • B. Dihydrofolate reductase (correct)

    Correct: methotrexate blocks dihydrofolate reductase.

  • C. Xanthine oxidase

    Xanthine oxidase is inhibited by allopurinol.

  • D. Ribonucleotide reductase

    Ribonucleotide reductase is inhibited by hydroxyurea.

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, Dihydrofolate reductase. Methotrexate inhibits dihydrofolate reductase, reducing tetrahydrofolate regeneration and thereby impairing nucleotide synthesis in rapidly dividing cells.

Why is "Thymidylate synthase" not the answer?

Thymidylate synthase is directly inhibited by 5-fluorouracil.

Why is "Xanthine oxidase" not the answer?

Xanthine oxidase is inhibited by allopurinol.

Why is "Ribonucleotide reductase" not the answer?

Ribonucleotide reductase is inhibited by hydroxyurea.

What concept does this question test?

It tests Nucleotide metabolism in Biochemistry. The correct option holds because: Correct: methotrexate blocks dihydrofolate reductase.

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 Nucleotide 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.