Amino acid metabolism: adrenal medulla epinephrine 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: adrenal medulla epinephrine synthesis

Sample item

The adrenal medulla secretes mainly epinephrine, whereas sympathetic nerve endings release norepinephrine. The medullary enzyme that makes epinephrine is induced by the high cortisol concentration reaching it from the surrounding cortex. Which enzyme is this?

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

The answer and the reasoning

A. Phenylethanolamine N-methyltransferase

Phenylethanolamine N-methyltransferase transfers a methyl group from S-adenosylmethionine to norepinephrine. Cortisol from the adrenal cortex, delivered through the intra-adrenal portal blood, induces it. Chromaffin cells are therefore rich in epinephrine, unlike nerve endings.

Option by option

  • A. Phenylethanolamine N-methyltransferase (correct)

    Correct. This methyltransferase converts norepinephrine to epinephrine and is cortisol-induced.

  • B. Tyrosine hydroxylase

    Tyrosine hydroxylase catalyses the rate-limiting first step, making DOPA, and is not specific to epinephrine.

  • C. Aromatic L-amino acid decarboxylase

    Aromatic L-amino acid decarboxylase converts DOPA to dopamine and acts well before epinephrine synthesis.

  • D. Dopamine beta-hydroxylase

    Dopamine beta-hydroxylase converts dopamine to norepinephrine and is also present in nerve endings.

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 A, Phenylethanolamine N-methyltransferase. Phenylethanolamine N-methyltransferase transfers a methyl group from S-adenosylmethionine to norepinephrine.

Why is "Tyrosine hydroxylase" not the answer?

Tyrosine hydroxylase catalyses the rate-limiting first step, making DOPA, and is not specific to epinephrine.

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

Aromatic L-amino acid decarboxylase converts DOPA to dopamine and acts well before epinephrine synthesis.

Why is "Dopamine beta-hydroxylase" not the answer?

Dopamine beta-hydroxylase converts dopamine to norepinephrine and is also present in nerve endings.

What concept does this question test?

It tests Amino acid metabolism: adrenal medulla epinephrine synthesis in Biochemistry. Cortisol from the adrenal cortex, delivered through the intra-adrenal portal blood, induces it. Chromaffin cells are therefore rich in epinephrine, unlike nerve endings.

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: adrenal medulla epinephrine 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.