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
Collagen contains amino acids Proline, Lysine and: 
Select and explain. 
A. Glycine, B. Isoleucine, C. Cysteine, D. Methionine
A: Glycine
Answer: A: Glycine 
Explanation: Ans. (a) GlycineGlycine* In collagen every third amino acid is glycine* Glycine is considered as the simplest amino acid* Properties of glycine: Non-essential, Glucogenic and optically inactive amino acid* Acts as a conjugating agent:# Conjugation of benzoic acid# Conjugation of bile acid* As neurotransmitter, it has both properties excitatory and inhibitory.Other amino acids present in collagen are: Proline, Hydroxyproline, Hydroxylysine Lysine (K)* An essential amino acid which is predominantly ketogenic* It is an amino acid which is deficient in cereals* Functions:# Important for covalent cross linkingin collagen# Precursor of carnitine = Lysine +Methionine