Disulphide bond is seen between-: (A) Lysine and cysteine, (B) Cysteine and cystine, (C) Cysteine and cysteine, (D) Arginine and histidine
Answer is C. But the question ask disulphide bond "is seen between" or in other words which two amino acids react to form disulphide bond. Two molecules of Cysteine join together to form Cystine, which has a disulfide bond (see fig). Cysteine cannot form disulfide bond with cystine. So disulphide bond is formed between two Cysteine molecules and not between Cysteine and Cystine