This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemistry of Lipids, Subject name: Biochemistry
[{'content': 'All of the following are Isoprene derivates (Polyprenoids), except ? \nSelect and explain. \nA. Ubiquitin, B. Dolichol, C. b-carotene, D. a-tocopherol', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Polyprenoids are a class of compounds synthesized from 5 carbon isoprene units. They include: Ubiquinone - electron carrier in respiratory chain Dolichol - long-chain alcohol involved in N-glycosylation Plant-derived Polyprenoids - rubber, camphor, the fat-soluble vitamins A, D, E, and K, and b-carotene (provitamin A). Ubiquitin is not a pa of polyprenoids. It is a protein (polypeptide).', 'role': 'assistant'}]