This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'In the citric acid cycle, the reaction which produces succinyl CoA also forms carbon dioxide. The key intermediate enzymic step involves: \nSelect and explain. \nA. The decarboxylation of a hydroxy acid, B. The decarboxylation of an alpha-ketoacid, C. The decarboxylation of a beta-ketoacid, D. The oxidation of a keto group to a carboxylic acid', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The enzyme is a-ketoglutarate dehydrogenase, an a-keto acid, which is decarboxylated. Therefore the second choice is correct. The only confusion might be with the last choice, since in effect it involves the oxidation of a keto group to a carboxylic acid. However, the product is the thio-ester of a carboxylic acid.', 'role': 'assistant'}]