<prompt> Keratin of skin and nail differ because ofDisulphide bondCovalent bondVander Waal bondHydrogen bond  <response>: 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 -Lippincotts 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. 