Amino acid metabolism: glutamate dehydrogenase regulation: 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 · Amino acid metabolism: glutamate dehydrogenase regulation

Sample item

Glutamate dehydrogenase carries out the main oxidative deamination in liver mitochondria. Which nucleotides inhibit it allosterically when the cell's energy charge is high?

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

The answer and the reasoning

B. GTP and ATP

Glutamate dehydrogenase is inhibited by GTP and ATP and activated by ADP and GDP. When energy is plentiful, deamination of glutamate to feed the TCA cycle is switched off; when energy is low it is stimulated.

Option by option

  • A. cAMP and cGMP

    Cyclic nucleotides are second messengers and are not the principal allosteric regulators of this enzyme.

  • B. GTP and ATP (correct)

    Correct. High-energy nucleotides GTP and ATP signal plentiful energy and inhibit the enzyme.

  • C. ADP and GDP

    These low-energy nucleotides are the allosteric activators, not inhibitors.

  • D. AMP and IMP

    These monophosphates regulate purine synthesis and glycogenolysis, not this deamination step.

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, GTP and ATP. Glutamate dehydrogenase is inhibited by GTP and ATP and activated by ADP and GDP.

Why is "cAMP and cGMP" not the answer?

Cyclic nucleotides are second messengers and are not the principal allosteric regulators of this enzyme.

Why is "ADP and GDP" not the answer?

These low-energy nucleotides are the allosteric activators, not inhibitors.

Why is "AMP and IMP" not the answer?

These monophosphates regulate purine synthesis and glycogenolysis, not this deamination step.

What concept does this question test?

It tests Amino acid metabolism: glutamate dehydrogenase regulation in Biochemistry. When energy is plentiful, deamination of glutamate to feed the TCA cycle is switched off; when energy is low it is stimulated.

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 Amino acid metabolism: glutamate dehydrogenase regulation?

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.