In the structure of pro - insulin in humans disulphide bonds exist between

Options

A. between B peptide and C peptide
B. between A peptide and B peptide
C. between C peptide and A peptide
D. between A and C peptide as well as B and C peptide

Answer

To solve the question regarding the structure of pro-insulin in humans and the existence of disulfide bonds, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Pro-insulin Structure**:
- Pro-insulin is a precursor molecule to insulin, consisting of three peptide chains: the A-peptide, B-peptide, and C-peptide.

2. **Identifying Peptide Chains**:
- The A-peptide and B-peptide are the two chains that will eventually form the active insulin molecule after the C-peptide is removed.

3. **Role of Disulfide Bonds**:
- Disulfide bonds are covalent bonds that form between the sulfur atoms of cysteine residues in proteins. They play a crucial role in stabilizing the three-dimensional structure of proteins.

4. **Locating Disulfide Bonds in Pro-insulin**:
- In pro-insulin, disulfide bonds are specifically formed between the A-peptide and B-peptide. This bonding is essential for the proper folding and stability of the insulin molecule.

5. **Final Confirmation**:
- Upon the cleavage of the C-peptide, the A-peptide and B-peptide remain connected by these disulfide bonds, forming the functional insulin molecule.

### Conclusion:
- Therefore, in the structure of pro-insulin in humans, disulfide bonds exist between the A-peptide and B-peptide.