Insulin Structure and Disulphide Linkages

Insulin is a hormone produced by the pancreas that plays a crucial role in regulating blood sugar levels. It consists of two polypeptide chains, known as the A chain and the B chain, which are connected by disulfide linkages. These disulfide linkages are formed between specific cysteine residues in the chains and are essential for the structure and function of insulin.

Disulfide Linkages in Insulin

Insulin contains three disulfide linkages, which are responsible for stabilizing its three-dimensional structure. These linkages form between the sulfur atoms of cysteine residues, which are amino acids that contain a sulfur atom in their side chains.

The disulfide linkages in insulin are as follows:

1. A7-B7: This disulfide linkage connects the A chain and the B chain at position 7. It forms between the sulfur atom of cysteine residue 7 in the A chain and the sulfur atom of cysteine residue 7 in the B chain.

2. A20-B19: This disulfide linkage connects the A chain and the B chain at position 20 and 19, respectively. It forms between the sulfur atom of cysteine residue 20 in the A chain and the sulfur atom of cysteine residue 19 in the B chain.

3. A6-A11: This disulfide linkage connects two cysteine residues within the A chain. It forms between the sulfur atoms of cysteine residue 6 and cysteine residue 11.

These three disulfide linkages contribute to the folding and stability of insulin's tertiary structure. They help to maintain the correct spatial arrangement of the A and B chains, which is crucial for insulin's ability to bind to its receptor and exert its biological effects.

Conclusion

In conclusion, insulin contains three disulfide linkages that connect the A and B chains and contribute to its overall structure and function. These linkages are formed between specific cysteine residues and play a crucial role in the stability and activity of insulin. Therefore, the correct answer is option 'B' - insulin has three disulfide linkages.