This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amino Acid Metabolic Disorder, Subject name: Biochemistry
[{'content': 'If tyrosine level in blood is normal without external supplementation, deficiency of which of the following is ruled out - \nSelect and explain. \nA. Tryptophan, B. Phenylalanine, C. Histidine, D. Isoleucine', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Phenylalanine o TyTosine is synthesized from phenylalanine.o In phenylalanine deficiency or in disorders in which phenylalanine cannot be converted into tyrosine (phenylketonuria), tyrosine becomes an essential amino acid and should be supplemented from outside.", 'role': 'assistant'}]