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
Cysteine is abundantly found in: 
Select and explain. 
A. Keratin, B. Chondroitin S04, C. Creatine, D. Spermine
A: Keratin
Answer: A: Keratin 
Explanation: 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