General Pathology USMLE Step 1 Practice Question
A 7-year-old boy presents with bleeding gums, perifollicular hemorrhages, and poor wound healing following a 6-month restrictive diet. Vital signs show HR 92/min, BP 105/68 mmHg, and RR 18/min. Serum vitamin C is 0.1 mg/dL (normal: >0.6). Skin biopsy from a healing wound demonstrates impaired collagen cross-linking with abnormal fibril formation. He denies joint pain or petechiae. Vitamin C is essential for which biochemical modification of collagen?
Answer choices
- AOxidation of cysteine residues in keratin
- BCleavage of procollagen by elastase
- CHydroxylation of proline and lysine residuesCorrect answer
- DCross linking of fibrin monomers
- ECarboxylation of glutamate residues
- FGlycosylation of hydroxylysine by galactosyltransferase enzymes
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