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
Methionine is synthesized from ? 
Select and explain. 
A. Cysteine, B. Glycine, C. Histidine, D. Arginine
A: Cysteine
Answer: A: Cysteine 
Explanation: Ans. is 'a' i.e.,Cysteine Methionine is a sulphar containing amino acid and is synthesized from cysteine.The precursor is homoserine, a product of reduction of aspaic acid.Homoserine is phosphorylated (by ATP) and the phosphate is then displaced by sulfhydryl group of cysteine to form cystathionine.Cleavage of alanine group from cystathionine yields homocysteine, which is methylated to yield methionine.