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 DNA sequences corresponding to chains A and B of human insulin and the bonds used to combine them, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**:
- Eli Lilly, an American company, created two DNA sequences that correspond to the A and B chains of human insulin.
- These sequences were introduced into plasmids of E. coli to produce the insulin chains.

2. **Identifying the Chains**:
- The chains A and B are the two separate peptide chains that make up the structure of insulin.
- Insulin is a protein hormone composed of two chains linked together.

3. **Production of Insulin**:
- After the E. coli bacteria produce the A and B chains, these chains need to be combined to form functional insulin.
- The process of combining these chains involves forming specific types of bonds.

4. **Types of Bonds in Proteins**:
- In proteins, there are several types of bonds that can hold the chains together:
- **Peptide Bonds**: These are the bonds that link amino acids together to form a protein.
- **Ionic Bonds**: These are formed between charged side chains of amino acids.
- **Hydrogen Bonds**: These are weak bonds that can occur between polar side chains.
- **Disulfide Bonds**: These are covalent bonds formed between the sulfur atoms of cysteine residues.

5. **Combining Chains A and B**:
- To form the complete insulin molecule, chains A and B must be linked together.
- The specific type of bond that is used to link these two chains is the **disulfide bond**. This bond is crucial for stabilizing the three-dimensional structure of the insulin molecule.

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

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