Vitamin C (ascorbic acid) is a water-soluble antioxidant that scavenges free radicals in aqueous compartments and regenerates alpha-tocopherol. A 40-year-old man with a 20-pack-year smoking history has marginal vitamin C intake. Which biochemical reaction in collagen synthesis is directly impaired by vitamin C deficiency?
- A Hydroxylation of proline and lysine residues ✓
- B Carboxylation of glutamate residues
- C Formation of triple helix from procollagen
- D Crosslinking of tropocollagen by lysyl oxidase
Correct answer: A. Hydroxylation of proline and lysine residues
Explanation
Vitamin C is an essential cofactor for prolyl hydroxylase and lysyl hydroxylase, which hydroxylate proline and lysine residues in procollagen. Without hydroxylation, hydrogen bonding is impaired, preventing stable triple helix formation. Carboxylation of glutamate requires vitamin K, and lysyl oxidase is copper-dependent.
Reference: Lehninger Principles of Biochemistry, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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