This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
[{'content': 'Selenocysteine is derivative of which amino acid? \nSelect and explain. \nA. Cysteine, B. Alanine, C. Arginine, D. Glycine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Selenocysteine is the 21st amino acid.its biosynthesis is by replacing oxygen from serine by selenium.cysteine is formed from serine (reversible). hence selenocysteine is formed from cysteineRef: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 215', 'role': 'assistant'}]