Amino acid metabolism: serine and threonine deamination: 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: serine and threonine deamination

Sample item

Most amino acids are deaminated by transamination followed by oxidative deamination of glutamate. Which pair is deaminated directly and non-oxidatively by pyridoxal phosphate-dependent dehydratases?

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

The answer and the reasoning

D. Serine and threonine

Serine dehydratase converts serine to pyruvate and ammonia, and threonine dehydratase converts threonine to alpha-ketobutyrate and ammonia. Both use pyridoxal phosphate and release ammonia without a redox step.

Option by option

  • A. Glutamate and glutamine

    Glutamate is deaminated oxidatively by glutamate dehydrogenase, and glutamine by glutaminase.

  • B. Lysine and arginine

    Lysine and arginine are not removed by dehydratase reactions.

  • C. Alanine and aspartate

    Alanine and aspartate are deaminated by transamination, not by dehydration.

  • D. Serine and threonine (correct)

    Correct. Both hydroxy amino acids lose water and ammonia through PLP-dependent dehydratases.

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 D, Serine and threonine. Serine dehydratase converts serine to pyruvate and ammonia, and threonine dehydratase converts threonine to alpha-ketobutyrate and ammonia.

Why is "Glutamate and glutamine" not the answer?

Glutamate is deaminated oxidatively by glutamate dehydrogenase, and glutamine by glutaminase.

Why is "Lysine and arginine" not the answer?

Lysine and arginine are not removed by dehydratase reactions.

Why is "Alanine and aspartate" not the answer?

Alanine and aspartate are deaminated by transamination, not by dehydration.

What concept does this question test?

It tests Amino acid metabolism: serine and threonine deamination in Biochemistry. Both use pyridoxal phosphate and release ammonia without a redox step.

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: serine and threonine deamination?

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.