Eli Lily an American company prepared two DNA sequence corresponing to A and B, chains of human insulin and introduced them in plasmids of E.coil to produce insulin chains. These chains A and B were

Options

A. Peptide bonds
B. Ionic bonds
C. H - bond
D. Disulphide bonds

Answer

To solve the question regarding the chains A and B of human insulin produced by Eli Lilly, we need to analyze the nature of the bonds that link these chains together after they are synthesized. Here’s a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Understanding Insulin Structure**: Human insulin consists of two polypeptide chains, known as the A chain and the B chain. These chains are linked together by specific types of bonds.

2. **Production of Chains**: Eli Lilly introduced the DNA sequences for the A and B chains of human insulin into plasmids of E. coli. This allows the bacteria to produce the insulin chains separately.

3. **Extraction of Chains**: After the E. coli bacteria produce the A and B chains, these chains are extracted from the bacterial cells.

4. **Combining the Chains**: The A and B chains of insulin are not directly linked in the initial production. To form functional insulin, these chains need to be combined.

5. **Type of Bonds Formed**: The A and B chains are linked together through disulfide bonds. Disulfide bonds are covalent bonds that form between the sulfur atoms of cysteine residues in the two chains. This is crucial for the proper folding and stability of the insulin molecule.

6. **Conclusion**: Therefore, the correct answer to the question is that the chains A and B were linked by **disulfide bonds**.

### Final Answer:
The chains A and B were **disulfide bonds**.