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': "Which of the following substrates links urea cycle to Kreb's cycle? \nSelect and explain. \nA. Fumarate, B. Oxaloacetate, C. Ornithine, D. Citrullin", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Arginosuccinate an intermediate of urea cycle is cleaved by argininosuccinate lyase to arginine and fumarate. This fumarate formed in the urea cycle can be funnelled into TCA cycle to be conveed to malate and then to oxaloacetate. Oxaloacetate formed in the krebs cycle can be transaminated to aspaate which is an intermediate of urea cycle. Ref: Textbook of Biochemistry By D M Vasudevan, 3rd Edition, Page 161', 'role': 'assistant'}]