Collagen: cross-linking and copper: 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 · Collagen: cross-linking and copper

Sample item

A male infant has hypotonia, seizures, sparse kinky hair and tortuous arteries, with low serum copper and ceruloplasmin. Which enzymatic defect explains the connective tissue abnormalities?

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

The answer and the reasoning

B. Reduced activity of copper-dependent lysyl oxidase

Menkes disease is an X-linked defect of the copper transporter ATP7A, so copper is trapped in the gut and cannot reach enzymes. Lysyl oxidase needs copper to form aldehydes from lysine and hydroxylysine for cross-links in collagen and elastin, producing weak vessel walls. Other copper enzymes such as dopamine beta-hydroxylase and cytochrome c oxidase are also affected.

Option by option

  • A. Deficient prolyl hydroxylase because of lack of vitamin C

    Prolyl hydroxylase deficiency from vitamin C lack causes scurvy, with normal copper.

  • B. Reduced activity of copper-dependent lysyl oxidase (correct)

    Correct. Lysyl oxidase is copper dependent and needed for cross-linking.

  • C. Defective procollagen N-peptidase

    N-peptidase deficiency causes dermatosparaxis type Ehlers-Danlos syndrome, with normal copper.

  • D. Deficient lysyl hydroxylase

    Lysyl hydroxylase deficiency causes kyphoscoliotic Ehlers-Danlos syndrome, with normal copper.

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 B, Reduced activity of copper-dependent lysyl oxidase. Menkes disease is an X-linked defect of the copper transporter ATP7A, so copper is trapped in the gut and cannot reach enzymes.

Why is "Deficient prolyl hydroxylase because of lack of vitamin C" not the answer?

Prolyl hydroxylase deficiency from vitamin C lack causes scurvy, with normal copper.

Why is "Defective procollagen N-peptidase" not the answer?

N-peptidase deficiency causes dermatosparaxis type Ehlers-Danlos syndrome, with normal copper.

Why is "Deficient lysyl hydroxylase" not the answer?

Lysyl hydroxylase deficiency causes kyphoscoliotic Ehlers-Danlos syndrome, with normal copper.

What concept does this question test?

It tests Collagen: cross-linking and copper in Biochemistry. Lysyl oxidase needs copper to form aldehydes from lysine and hydroxylysine for cross-links in collagen and elastin, producing weak vessel walls. Other copper enzymes such as dopamine beta-hydroxylase and cytochrome c oxidase are also affected.

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 Collagen: cross-linking and copper?

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.