Vitamins: vitamin K: 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.

Try it

Biochemistry · Vitamins: vitamin K

Sample item

A newborn who was not given vitamin K at birth bleeds from the umbilical stump on day 5. Which post-translational modification, dependent on vitamin K, is impaired?

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

The answer and the reasoning

B. Gamma-carboxylation of glutamate residues in factors II, VII, IX and X

Vitamin K is a cofactor for gamma-glutamyl carboxylase, which carboxylates glutamate residues on factors II, VII, IX, X and proteins C and S. The carboxyglutamate groups bind calcium and allow the factors to attach to phospholipid surfaces. Warfarin blocks the recycling of vitamin K.

Option by option

  • A. Transamination of amino acids

    Transamination requires pyridoxal phosphate (vitamin B6).

  • B. Gamma-carboxylation of glutamate residues in factors II, VII, IX and X (correct)

    Correct. Without gamma-carboxylation the clotting factors are inactive.

  • C. Hydroxylation of proline residues in collagen

    Hydroxylation of proline in collagen requires vitamin C.

  • D. Methylation of homocysteine

    Methylation of homocysteine to methionine requires vitamin B12 and folate.

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 B, Gamma-carboxylation of glutamate residues in factors II, VII, IX and X. Vitamin K is a cofactor for gamma-glutamyl carboxylase, which carboxylates glutamate residues on factors II, VII, IX, X and proteins C and S.

Why is "Transamination of amino acids" not the answer?

Transamination requires pyridoxal phosphate (vitamin B6).

Why is "Hydroxylation of proline residues in collagen" not the answer?

Hydroxylation of proline in collagen requires vitamin C.

Why is "Methylation of homocysteine" not the answer?

Methylation of homocysteine to methionine requires vitamin B12 and folate.

What concept does this question test?

It tests Vitamins: vitamin K in Biochemistry. The carboxyglutamate groups bind calcium and allow the factors to attach to phospholipid surfaces. Warfarin blocks the recycling of vitamin K.

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 Vitamins: vitamin K?

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.