(a) Explain the role of regulatory gene, operator and structural genes in lac operon when E. Coli is growing in a culture medium with the sources of energy as lactose.

Explanation

### Step-by-Step Solution:

1. **Understanding the Lac Operon**:
- The lac operon is a genetic system found in E. coli that is responsible for the metabolism of lactose. It consists of regulatory genes, an operator, and structural genes.

2. **Components of the Lac Operon**:
- **Regulatory Gene (I gene)**: This gene produces a repressor protein that regulates the operon. In the absence of lactose, this repressor binds to the operator, preventing transcription of the structural genes.
- **Operator**: This is a segment of DNA where the repressor protein binds. When the repressor is attached to the operator, RNA polymerase cannot access the structural genes, thus inhibiting transcription.
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