This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of lipid, Subject name: Biochemistry
[{'content': 'Which is the first intermediate in the conversion of cholesterol to bile acids? \nSelect and explain. \nA. Ergosterol, B. Lanosterol, C. 7- hydroxycholesterol, D. 7- dehydrocholesterol', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The first intermediate in the synthesis of bile acids is 7a-hydroxycholesterol. It is catalyzed by the enzyme 7a-hydroxylase, a microsomal CYP450 enzyme, which requires NADPH, oxygen, and vitamin C as cofactors. It is the rate-limiting step in the synthesis of bile acids.', 'role': 'assistant'}]