This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Structure & Function of Proteins), Subject name: Biochemistry
[{'content': 'Keratin of skin and nail differ because of \nSelect and explain. \nA. Disulphide bond, B. Covalent bond, C. Vander Waal bond, D. Hydrogen bond', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e Disulphide bond " the keratins are a family of closely related fibrous proteins, whose structure is nearly entirely alpha- helical. They are a major component of tissues such as hairs and skin; their rigidity is determined by the number of disulphide bonds between the constituent polypeptide chains " -Lippincott\'s BiochemThus the difference in rigidity between the keratins of hairs and nail in because of the number of disulphide bonds.Keratins are rich in cysteine*( a sulphur containing amino acid ) which provides covalent disulphide cross-link between adjacent polypeptide chains.', 'role': 'assistant'}]