How many structural genes are present is lac-operon of E.coli?

Options

A. 4
B. 3
C. 2
D. 1

Answer

To answer the question of how many structural genes are present in the lac operon of E. coli, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Lac Operon**: The lac operon is a genetic system in E. coli that allows the bacteria to utilize lactose as an energy source. It is composed of several components including structural genes, a promoter, and an operator.

2. **Identify the Components**: The lac operon consists of three main structural genes: lacZ, lacY, and lacA. Each of these genes has a specific function related to lactose metabolism.

3. **List the Structural Genes**:
- **lacZ**: This gene encodes the enzyme beta-galactosidase, which breaks down lactose into glucose and galactose.
- **lacY**: This gene encodes permease, which facilitates the transport of lactose into the cell.
- **lacA**: This gene encodes transacetylase, which is involved in the metabolism of lactose.

4. **Count the Structural Genes**: From the above, we can see that there are three structural genes in total in the lac operon.

5. **Conclusion**: Therefore, the answer to the question is that there are **3 structural genes** present in the lac operon of E. coli.

### Final Answer:
The lac operon of E. coli contains **3 structural genes**.

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