Regulation of lac operon by repressor is called

Options

A. Negative regulation
B. Positive regulation
C. Neutral regulation
D. Both (2) and (3)

Answer

To solve the question regarding the regulation of the lac operon by a repressor, 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 is controlled by regulatory mechanisms that respond to the presence or absence of lactose.

**Hint**: Recall that the lac operon consists of structural genes (lacZ, lacY, and lacA) and regulatory elements (promoter and operator).

2. **Role of the Repressor**:
- The lac operon is primarily regulated by a repressor protein, which binds to the operator region of the operon. When the repressor is bound to the operator, it prevents RNA polymerase from accessing the promoter and transcribing the genes necessary for lactose metabolism.

**Hint**: Think about how the binding of the repressor affects gene expression.

3. **Definition of Negative Regulation**:
- Negative regulation occurs when a repressor inhibits gene expression. In the case of the lac operon, the binding of the repressor to the operator is an example of negative regulation because it prevents transcription.

**Hint**: Consider the terminology: "negative" implies inhibition or prevention.

4. **Inducer Role**:
- When lactose (or an analog like IPTG) is present, it acts as an inducer by binding to the repressor. This binding causes a conformational change in the repressor, preventing it from binding to the operator. As a result, RNA polymerase can bind to the promoter, leading to the transcription of the operon.

**Hint**: Remember that the presence of the inducer shifts the regulation from negative to positive.

5. **Conclusion**:
- The question specifically asks about the regulation of the lac operon by the repressor. Since the repressor inhibits transcription, this regulation is classified as negative regulation.

**Hint**: Focus on the specific action of the repressor to determine the type of regulation.

### Final Answer:
The regulation of the lac operon by the repressor is called **negative regulation**.