Which one of the following TCA cycle intermediate may not be added or removed by other metabolic pathways?: (A) Oxaloacetate, (B) Isocitrate, (C) Citrate, (D) Fumarate
Answer is B. 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