Amino acid metabolism: polyamine 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 · Amino acid metabolism: polyamine synthesis

Sample item

A patient with late-stage African trypanosomiasis is treated with eflornithine, a suicide inhibitor of the enzyme that decarboxylates an amino acid to make putrescine, the precursor of spermidine and spermine. Which enzyme is blocked?

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

The answer and the reasoning

C. Ornithine decarboxylase

Ornithine decarboxylase makes putrescine, the first step of polyamine synthesis, and polyamines are needed for rapidly dividing cells such as trypanosomes. Spermidine is then formed by adding an aminopropyl group from decarboxylated S-adenosylmethionine.

Option by option

  • A. Aromatic L-amino acid decarboxylase

    This enzyme makes dopamine and serotonin from DOPA and 5-hydroxytryptophan.

  • B. Glutamate decarboxylase

    Glutamate decarboxylase makes the neurotransmitter GABA, which is unrelated to polyamines.

  • C. Ornithine decarboxylase (correct)

    Correct. Decarboxylation of ornithine to putrescine begins polyamine synthesis and is the target.

  • D. Histidine decarboxylase

    Histidine decarboxylase makes histamine and is not involved in putrescine 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, Ornithine decarboxylase. Ornithine decarboxylase makes putrescine, the first step of polyamine synthesis, and polyamines are needed for rapidly dividing cells such as trypanosomes.

Why is "Aromatic L-amino acid decarboxylase" not the answer?

This enzyme makes dopamine and serotonin from DOPA and 5-hydroxytryptophan.

Why is "Glutamate decarboxylase" not the answer?

Glutamate decarboxylase makes the neurotransmitter GABA, which is unrelated to polyamines.

Why is "Histidine decarboxylase" not the answer?

Histidine decarboxylase makes histamine and is not involved in putrescine formation.

What concept does this question test?

It tests Amino acid metabolism: polyamine synthesis in Biochemistry. Spermidine is then formed by adding an aminopropyl group from decarboxylated S-adenosylmethionine.

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: polyamine 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.