Vitamins: ascorbic acid and collagen: 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: ascorbic acid and collagen

Sample item

A 70-year-old man living alone on a tea-and-toast diet has bleeding gums, perifollicular haemorrhages, corkscrew hairs and poor wound healing. Which biochemical process is impaired?

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

The answer and the reasoning

B. Hydroxylation of proline and lysine residues in procollagen

He has scurvy. Ascorbic acid keeps the iron of prolyl and lysyl hydroxylases in the reduced ferrous state. Without it, procollagen is under-hydroxylated, cannot form a stable triple helix and is degraded, which weakens capillaries and delays wound healing.

Option by option

  • A. Oxidative deamination of lysine by lysyl oxidase

    Lysyl oxidase is a copper-dependent enzyme, not vitamin C dependent.

  • B. Hydroxylation of proline and lysine residues in procollagen (correct)

    Vitamin C is the cofactor for the hydroxylases that stabilise collagen, so deficiency causes fragile vessels.

  • C. Cross-linking of collagen by transglutaminase

    Transglutaminase cross-linking occurs in fibrin and is not the lesion of scurvy.

  • D. Gamma-carboxylation of glutamate residues in clotting factors

    Gamma-carboxylation of clotting factors requires vitamin K, and its deficiency gives a coagulopathy.

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, Hydroxylation of proline and lysine residues in procollagen. He has scurvy.

Why is "Oxidative deamination of lysine by lysyl oxidase" not the answer?

Lysyl oxidase is a copper-dependent enzyme, not vitamin C dependent.

Why is "Cross-linking of collagen by transglutaminase" not the answer?

Transglutaminase cross-linking occurs in fibrin and is not the lesion of scurvy.

Why is "Gamma-carboxylation of glutamate residues in clotting factors" not the answer?

Gamma-carboxylation of clotting factors requires vitamin K, and its deficiency gives a coagulopathy.

What concept does this question test?

It tests Vitamins: ascorbic acid and collagen in Biochemistry. Ascorbic acid keeps the iron of prolyl and lysyl hydroxylases in the reduced ferrous state. Without it, procollagen is under-hydroxylated, cannot form a stable triple helix and is degraded, which weakens capillaries and delays wound healing.

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: ascorbic acid and collagen?

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.