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 one of the following TCA cycle intermediate may not be added or removed by other metabolic pathways? \nSelect and explain. \nA. Oxaloacetate, B. Isocitrate, C. Citrate, D. Fumarate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Oxaloacetate may be formed from pyruvate during gluconeogenesis. Degradation of tyrosine and phenylalanine may produce fumarate. Citrate is transpoed out of mitochondria to be used as a source of cytoplasmic acetyl CoA. Isocitrate is formed and removed in TCA cycle. Ref: Textbook of Biochemistry for Medical Students by D.M. Vasudevan, 6th Edition, Page: 218', 'role': 'assistant'}]