This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
[{'content': 'In collagen synthesis, hydroxyproline is formed from \nSelect and explain. \nA. Proline, B. Lysine, C. Hydroxylysine, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Collagen is initially synthesized as a larger precursor polypeptide, pro-collagen. Numerous prolyl and lysyl residues of pro-collagen are hydroxylated by prolyl hydroxylase and lysyl hydroxylase, enzymes that require ascorbic acid (vitamin C). Hydroxy-prolyl and hydroxy-lysyl residues provide additional hydrogen bonding capability that stabilizes the mature protein. In addition, glucosyl and galactosyltransferases attach glucosyl or galactosyl residues to the hydroxyl groups of specific hydroxy-lysyl residues.Ref: Harper 28th Ed. Page-41, Harper 27th Ed. Page-39', 'role': 'assistant'}]