This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'Cystine is formed by ? \nSelect and explain. \nA. Hydroxylation of cysteine molecule, B. Carboxylation of cysteine molecule, C. Peptide bond between two cysteine molecule, D. Disulfide bond between cysteine molecule', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Disulfide bond between cysteine molecule", 'role': 'assistant'}]