Amino acid metabolism: branched-chain amino acids: 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: branched-chain amino acids

Sample item

After a protein-rich meal, plasma levels of branched-chain amino acids rise less than other amino acids because the liver largely spares them. Which tissue mainly takes up and transaminates them?

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

The answer and the reasoning

A. Skeletal muscle

Branched-chain aminotransferase is mainly present in skeletal muscle and other peripheral tissues, while hepatic activity is low. Muscle is therefore the main site of their first catabolic step, and the keto acids are released for oxidation elsewhere.

Option by option

  • A. Skeletal muscle (correct)

    Correct. Muscle holds most branched-chain aminotransferase activity.

  • B. Erythrocyte

    Erythrocytes have no mitochondria for oxidative catabolism of amino acids.

  • C. Liver

    The liver has low branched-chain aminotransferase activity.

  • D. Renal cortex

    The renal cortex does not take up most dietary branched-chain amino acids.

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, Skeletal muscle. Branched-chain aminotransferase is mainly present in skeletal muscle and other peripheral tissues, while hepatic activity is low.

Why is "Erythrocyte" not the answer?

Erythrocytes have no mitochondria for oxidative catabolism of amino acids.

Why is "Liver" not the answer?

The liver has low branched-chain aminotransferase activity.

Why is "Renal cortex" not the answer?

The renal cortex does not take up most dietary branched-chain amino acids.

What concept does this question test?

It tests Amino acid metabolism: branched-chain amino acids in Biochemistry. Muscle is therefore the main site of their first catabolic step, and the keto acids are released for oxidation elsewhere.

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: branched-chain amino acids?

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.