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 most commonly contains which of the following amino acid: 
Select and explain. 
A. Proline and hydroxyproline, B. Cysteine and cysteine, C. Glycine and cysteine, D. Methionine and proline
A: Proline and hydroxyproline
Answer: A: Proline and hydroxyproline 
Explanation: Ans. a. Proline and hydroxyprolineAMINO ACIDS REQUIRED FOR SPECIAL PRODUCTSSpecial productAmino acid requiredCollagenGlycine +Proline+HydroxyprolineElastinGlycine+Alanine+Valine+ProlineCreatineGlycine+Arginine+MethioninePurineGlycine+Aspartate+Glutamine+SerinePyrimidineAspartate+GlutamineGlutathioneGlycine+Cysteine+GlutamateHistoneArginine+HistidineCarnosineb-alanine+HistidineHemoglobinHistidine+Arginine+LysineKeratinHistidine:Arginine:Lysine=1:12:4CholineMethionine+Glycine+Serine+B6CarnitineLysine+Methionine