This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amino Acids Basics, Subject name: Biochemistry
Which amino acid spares the use of methionine - 
Select and explain. 
A. Cysteine, B. Glycine, C. Histidine, D. Arginine
A: Cysteine
Answer: A: Cysteine 
Explanation: Ans. is 'a' i.e., Cysteine "Adequate dietary source of cysteine 'spares ' methionine".o Methionine is an essential amino acid.o Methionine is required for synthesis of cysteine (thus cysteine is non-essential amino acid)o Thus, cysteine can spare the requirment of methionine in diet.