This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Which amino acid required in infants and not in adults? 
Select and explain. 
A. Histidine, B. Glycine, C. Isoleucine, D. Valine
A: Histidine
Answer: A: Histidine 
Explanation: Ans. is 'a' i.e., Histidine* Histidine and Arginine are partially or semiessential aminoacids. They are synthesized by metabolic pathways but the rate of synthesis is low, that the endogenous synthesis is not sufficient to meet the requirements during periods of increased demand like during growth* Glycine is a non-essential aminoacid as it can be synthesized from serine, threonine and reversal of glycine cleavage system* Isoleucine and Valine are essential aminoacids.