What was the challenge for production of insulin using rDNA techniques ?
How did Eli Lilly produce insulin using rDNA technology?

Explanation

### Step-by-Step Solution:

1. **Identify the Challenge**: The primary challenge in producing insulin using recombinant DNA (rDNA) technology was to assemble the insulin into its mature form. Insulin consists of two chains, A and B, which need to be combined correctly to form the functional hormone.

2. **Preparation of DNA Sequences**: In 1983, the American company Eli Lilly prepared two separate DNA sequences that corresponded to the A and B chains of human insulin. This was the first step in the production process.

3. **Introduction into Plasmids**: The next step involved introducing these two DNA sequences into plasmids. Plasmids are small circular DNA molecules that can replicate independently within a bacterial cell. Eli Lilly used plasmids from the bacterium E. coli for this purpose.

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