The repressor of the lac operon is synthesised all the time constitutively from the

Options

A. p gene
B. i gene
C. z gene
D. o gene

Answer

To solve the question regarding the synthesis of the repressor of the lac operon, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Lac Operon**:
The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of structural genes (Z, Y, A), a promoter (P), an operator (O), and regulatory elements.

**Hint**: Remember that the lac operon is responsible for lactose metabolism in bacteria.

2. **Identifying the Repressor**:
The repressor protein is crucial for the regulation of the lac operon. It binds to the operator region (O) of the operon to prevent transcription when lactose is not present.

**Hint**: The repressor prevents transcription when lactose is absent.

3. **Source of the Repressor**:
The repressor is synthesized from a specific gene. In the case of the lac operon, this gene is known as the I gene (inducer gene). The I gene is responsible for the constant production of the repressor protein.

**Hint**: Look for the gene that is responsible for the continuous synthesis of the repressor.

4. **Function of the Repressor**:
When lactose or its derivative allolactose is present, it binds to the repressor, causing a conformational change that inactivates the repressor. This allows RNA polymerase to access the promoter and initiate transcription of the operon.

**Hint**: The presence of lactose inactivates the repressor, allowing transcription to occur.

5. **Conclusion**:
Therefore, the repressor of the lac operon is synthesized all the time constitutively from the I gene.

**Final Answer**: The correct option is **I gene**.

### Summary of Steps:
1. Understand the lac operon structure.
2. Identify the role of the repressor.
3. Determine the source of the repressor (I gene).
4. Explain the function of the repressor in the presence of lactose.
5. Conclude with the correct answer.