Amino acids: phenylketonuria: 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 acids: phenylketonuria

Sample item

Which dietary intervention is central in phenylketonuria?

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

The answer and the reasoning

C. Restrict phenylalanine and supplement tyrosine

Phenylketonuria impairs conversion of phenylalanine to tyrosine, making tyrosine conditionally essential. Early phenylalanine restriction prevents severe neurodevelopmental injury.

Option by option

  • A. Restrict tyrosine and supplement phenylalanine

    Tyrosine is needed because it cannot be made adequately in PKU.

  • B. Eliminate all carbohydrates

    Carbohydrate elimination does not correct the enzyme defect.

  • C. Restrict phenylalanine and supplement tyrosine (correct)

    Correct. Phenylalanine is restricted and tyrosine is supplemented.

  • D. Increase branched-chain amino acids only

    Branched-chain amino acids are unrelated to phenylalanine metabolism.

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, Restrict phenylalanine and supplement tyrosine. Phenylketonuria impairs conversion of phenylalanine to tyrosine, making tyrosine conditionally essential.

Why is "Restrict tyrosine and supplement phenylalanine" not the answer?

Tyrosine is needed because it cannot be made adequately in PKU.

Why is "Eliminate all carbohydrates" not the answer?

Carbohydrate elimination does not correct the enzyme defect.

Why is "Increase branched-chain amino acids only" not the answer?

Branched-chain amino acids are unrelated to phenylalanine metabolism.

What concept does this question test?

It tests Amino acids: phenylketonuria in Biochemistry. Early phenylalanine restriction prevents severe neurodevelopmental injury.

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 acids: phenylketonuria?

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.