This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Methionine and Cysteine details, Subject name: Biochemistry
[{'content': 'Homocysteine is \nSelect and explain. \nA. Amino-acid in Protein- D form, B. Amino-acid in Protein- L form, C. Non-protein alpha amino-acid, D. Seen in Collagen', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Homocysteine is a non-proteinogenic alpha- amino acid Homologous to cysteine, differing by an additional methylene bridge (-CH2-) Synthesized from methionine.', 'role': 'assistant'}]