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
Amino-acid expressed maximally in collagen? 
Select and explain. 
A. Tyrosine & phenylalanine, B. Alanine & aspaic acid, C. Glycine & cysteine, D. Proline & hydroxyproline
D: Proline & hydroxyproline
Answer: D: Proline & hydroxyproline 
Explanation: Ans. is `d' i.e., Proline & hydroxyprolineGlycine (33%), proline (10%), hydroxyproline, lysine and hydroxylysine are the predominant amino acids in collagen. Collagen.