Biomolecules and enzymes: gamma-carboxyglutamate: 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 · Biomolecules and enzymes: gamma-carboxyglutamate

Sample item

A patient on warfarin has factors II, VII, IX and X that cannot bind calcium and attach to phospholipid surfaces. Which modified amino acid residue is deficient in these proteins?

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

The answer and the reasoning

C. Gamma-carboxyglutamate

Vitamin K-dependent carboxylase converts specific glutamate residues to gamma-carboxyglutamate after translation. The extra carboxyl group lets the clotting factor chelate calcium and bind membrane phospholipid. Warfarin blocks vitamin K epoxide reductase, so under-carboxylated factors are made.

Option by option

  • A. 4-Hydroxyproline

    4-Hydroxyproline is made by prolyl hydroxylase and needs vitamin C; it stabilises collagen, not clotting factors.

  • B. Selenocysteine

    Selenocysteine is incorporated co-translationally into selenoproteins such as glutathione peroxidase and is unrelated to warfarin.

  • C. Gamma-carboxyglutamate (correct)

    Correct. Gamma-carboxyglutamate residues bind calcium, and warfarin prevents their formation.

  • D. 5-Hydroxylysine

    5-Hydroxylysine is a collagen residue made by lysyl hydroxylase and is used for cross-links and glycosylation.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Gamma-carboxyglutamate. Vitamin K-dependent carboxylase converts specific glutamate residues to gamma-carboxyglutamate after translation.

Why is "4-Hydroxyproline" not the answer?

4-Hydroxyproline is made by prolyl hydroxylase and needs vitamin C; it stabilises collagen, not clotting factors.

Why is "Selenocysteine" not the answer?

Selenocysteine is incorporated co-translationally into selenoproteins such as glutathione peroxidase and is unrelated to warfarin.

Why is "5-Hydroxylysine" not the answer?

5-Hydroxylysine is a collagen residue made by lysyl hydroxylase and is used for cross-links and glycosylation.

What concept does this question test?

It tests Biomolecules and enzymes: gamma-carboxyglutamate in Biochemistry. The extra carboxyl group lets the clotting factor chelate calcium and bind membrane phospholipid. Warfarin blocks vitamin K epoxide reductase, so under-carboxylated factors are made.

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 Biomolecules and enzymes: gamma-carboxyglutamate?

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.