Nucleotide metabolism: reciprocal regulation of AMP and GMP synthesis: 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: reciprocal regulation of AMP and GMP synthesis

Sample item

From inosine monophosphate, adenylate synthesis needs GTP, whereas guanylate synthesis needs ATP. What is the metabolic advantage of this arrangement?

AIt makes purine synthesis independent of PRPPBIt prevents formation of uric acidCIt speeds degradation of excess nucleotidesDIt balances adenine and guanine nucleotide pools

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

The answer and the reasoning

D. It balances adenine and guanine nucleotide pools

Conversion of IMP to AMP uses GTP as energy source, and conversion to GMP uses ATP. High GTP therefore promotes adenylate synthesis, and high ATP promotes guanylate synthesis, so neither pool grows at the expense of the other. AMP and GMP also feed back to inhibit their own formation.

Option by option

A. It makes purine synthesis independent of PRPP
PRPP is still needed at the first committed step of purine synthesis.
B. It prevents formation of uric acid
Uric acid forms from catabolism of purines and is not prevented by this mechanism.
C. It speeds degradation of excess nucleotides
The arrangement governs synthesis, not degradation of nucleotides.
D. It balances adenine and guanine nucleotide pools (correct)
Correct. Each branch is driven by the opposite nucleotide, balancing the two pools.

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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, It balances adenine and guanine nucleotide pools. Conversion of IMP to AMP uses GTP as energy source, and conversion to GMP uses ATP.

Why is "It makes purine synthesis independent of PRPP" not the answer?

PRPP is still needed at the first committed step of purine synthesis.

Why is "It prevents formation of uric acid" not the answer?

Uric acid forms from catabolism of purines and is not prevented by this mechanism.

Why is "It speeds degradation of excess nucleotides" not the answer?

The arrangement governs synthesis, not degradation of nucleotides.

What concept does this question test?

It tests Nucleotide metabolism: reciprocal regulation of AMP and GMP synthesis in Biochemistry. High GTP therefore promotes adenylate synthesis, and high ATP promotes guanylate synthesis, so neither pool grows at the expense of the other. AMP and GMP also feed back to inhibit their own formation.

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 Nucleotide metabolism: reciprocal regulation of AMP and GMP synthesis?

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.