Eli Lilly, an American company prepared two DNA sequences corresponding to A and B, chains of human insulin, and introduced them in plasmids of E. Coli to produce insulin chains. Chains A and B were produced separately, extracted and combined by creating

Options

A. Peptide bonds
B. Ionic bonds
C. H-bonds
D. Disulfide bonds

Answer

To answer the question about how Eli Lilly combined the A and B chains of human insulin after they were produced separately in E. coli, we can break down the process step by step.

### Step-by-Step Solution:

1. **Preparation of DNA Sequences**: Eli Lilly prepared two DNA sequences that correspond to the A and B chains of human insulin. These sequences are essential for the production of the respective peptide chains.

**Hint**: Understand that DNA sequences are the templates for synthesizing proteins.

2. **Introduction into Plasmids**: The DNA sequences for the A and B chains were introduced into plasmids, which are small circular DNA molecules used to transfer genetic material into bacteria.

**Hint**: Plasmids are crucial tools in biotechnology for gene cloning and expression.

3. **Transformation of E. coli**: The plasmids containing the insulin DNA sequences were introduced into E. coli bacteria. This process is known as transformation, allowing the bacteria to produce the insulin chains.

**Hint**: Know the role of E. coli as a host for producing recombinant proteins.

4. **Production of Insulin Chains**: The transformed E. coli bacteria expressed the genes and produced the A and B chains of insulin separately.

**Hint**: Remember that bacteria can be engineered to produce human proteins through genetic manipulation.

5. **Extraction of Chains**: After the production phase, the A and B chains were extracted from the E. coli cells. This involves breaking open the cells and purifying the insulin chains.

**Hint**: Extraction is a key step in isolating the desired proteins from the host cells.

6. **Combination of Chains**: The extracted A and B chains were combined to form pro-insulin. This combination is achieved by creating disulfide bonds between the two chains.

**Hint**: Disulfide bonds are important for the structural integrity of proteins, especially in insulin.

7. **Removal of C-Peptide**: In the final step, the C-peptide, which is part of pro-insulin, is removed to yield mature insulin. The mature insulin consists only of the A and B chains linked by disulfide bonds.

**Hint**: The C-peptide is not present in the mature form of insulin, which is crucial for its biological activity.

### Final Answer:
The A and B chains of human insulin were combined by creating **disulfide bonds** between them.