In insulin structure.:- A chain has total 21 Amino Acid. 6th, 7th, 11th, and 20th Amino Acid Are Cysteine and these residuals are responsible for the formation of disulphide bond. If we break disulphide bond in a protein this will lead to denaturation of the protein. B Chain has total 30 amino acid.7th and 19th are cysteine So they also cannot be changed, or if changed will lead to denaturation of the protein Thus options C and D can be ruled out. Interchange of A1 & A4, i.e. glycine and glutamate, which can also be ruled out because glycine is an amino acid which is conserved during evolution in most of the proteins. Interchange of B29 and B30: - The insulin which is used in the treatment - Insulin lispro actually has a change in the carboxy terminal of B chain. So, changes can be made here for changing little bit of propeies and not going to damage the structure much. EXTRA EDGE: Gene coding for insulinis localized on11p15 site of chromosome.