This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure & Function of Protein, Subject name: Biochemistry
Amino acid abundant in collagen: 
Select and explain. 
A. Glycine, B. Lysine, C. Leucine, D. Isoleucine
A: Glycine
Answer: A: Glycine 
Explanation: Ans. A Glycine* Collagen is rich in glycine and proline amino acid.* Glycine is the smallest amino acid, present in every third position of chain, therefore it fits into the spaces where the three chains of helix comes together.* This repeating structure, represented as (Gly-X-Y) n, is an absolute requirement for the formation of the triple helix. While X and Y can be any other amino acid, about 100 of the X positions are proline and about 100 of the Y positions are hydroxyproline. Proline and hydroxyproline confer rigidity on the collagen molecule.