Nucleotide metabolism: CTP synthetase: 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: CTP synthetase

Sample item

In pyrimidine synthesis, UTP is converted to CTP by amination. Which compound provides the amino group in the human enzyme CTP synthetase?

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

The answer and the reasoning

C. Glutamine

CTP synthetase transfers the amide nitrogen of glutamine to UTP in an ATP-dependent reaction. CTP then feeds back to inhibit the enzyme. Glutamine is also the nitrogen donor for carbamoyl phosphate synthetase II and for several steps of purine synthesis.

Option by option

  • A. Asparagine

    Asparagine is made from aspartate using glutamine and is not the donor in this reaction.

  • B. Aspartate

    Aspartate supplies atoms to the pyrimidine ring but not the amino group added to UTP.

  • C. Glutamine (correct)

    Correct. Glutamine is the nitrogen donor for amination of UTP.

  • D. Glycine

    Glycine contributes atoms to the purine ring and not to CTP formation.

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 C, Glutamine. CTP synthetase transfers the amide nitrogen of glutamine to UTP in an ATP-dependent reaction.

Why is "Asparagine" not the answer?

Asparagine is made from aspartate using glutamine and is not the donor in this reaction.

Why is "Aspartate" not the answer?

Aspartate supplies atoms to the pyrimidine ring but not the amino group added to UTP.

Why is "Glycine" not the answer?

Glycine contributes atoms to the purine ring and not to CTP formation.

What concept does this question test?

It tests Nucleotide metabolism: CTP synthetase in Biochemistry. CTP then feeds back to inhibit the enzyme. Glutamine is also the nitrogen donor for carbamoyl phosphate synthetase II and for several steps of purine synthesis.

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: CTP synthetase?

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.