A 60-year-old man with a diet lacking fresh fruits and vegetables for months presents with bleeding gums, perifollicular hemorrhages, and poor wound healing. The defective step in collagen synthesis involves which post-translational modification?

• A Cleavage of terminal propeptides by peptidases
• B Glycosylation of hydroxylysine residues
• C Cross-linking of tropocollagen by lysyl oxidase
• D Hydroxylation of proline and lysine residues ✓

Explanation

Vitamin C is a cofactor for prolyl-4-hydroxylase and lysyl hydroxylase in the rough endoplasmic reticulum. Without hydroxylation, alpha chains cannot form the stable triple helix, producing unstable collagen that degrades, hence bleeding, poor healing, and capillary fragility. Lysyl oxidase cross-linking is copper-dependent, not vitamin C-dependent, which kills option C as the tempting distractor.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.