This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
[{'content': 'Which of the following is a modified amino acid? \nSelect and explain. \nA. Arginine, B. Cysteine, C. Asparagine, D. Threonine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Two molecules of cysteine make cysteine (cys-cys) or dithio b, b-a amino propionic acid. The SS linkage is called as disulfide bridge. Ref: Textbook of medical biochemistry, MN Chatterji, 8th edition, page no: 78', 'role': 'assistant'}]