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
[{'content': 'Cysteine is abundantly found in: \nSelect and explain. \nA. Keratin, B. Chondroitin S04, C. Creatine, D. Spermine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: a (Keratin) Ref:Vasudevan, 4th ed, p.178; 5th ed, p. 191Cysteine is found in large quantities in keratin of hair and nails.Products of amino acids:TyrosineThyroid hormonesMelaninCatecholaminesThvptophanSerotoninMelatoninNADNADPArginineNitri oxideGlutamateGABAHistidineHistanineFIGLUOrnithine + methionineSpermineSpermidineGlycine+Arginine + MethionineCreatinine', 'role': 'assistant'}]