In lac-operon , which protein is not regulated by the repressor?

Options

A. Galactosidase
B. Lactose permease
C. Tryptophan synthetase
D. Transacetylase

Answer

To solve the question about which protein is not regulated by the repressor in the lac operon, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Lac Operon Structure**: The lac operon consists of a regulatory gene and structural genes. The regulatory gene produces a repressor protein that can bind to the operator region of the operon.

2. **Identify the Structural Genes**: The structural genes in the lac operon are:
- Z gene: Codes for beta-galactosidase
- Y gene: Codes for permease
- A gene: Codes for transacetylase

3. **Role of the Repressor**: The repressor protein binds to the operator region when lactose (the inducer) is absent, preventing the transcription of the structural genes (Z, Y, A). When lactose is present, it binds to the repressor, inactivating it, allowing transcription to occur.

4. **Analyze the Given Options**: The question provides four options:
- Beta-galactosidase
- Lactose
- Tryptophan synthetase
- Transacetylase

5. **Determine Which Protein is Not Regulated**:
- Beta-galactosidase, permease, and transacetylase are all products of the lac operon and are regulated by the repressor.
- Tryptophan synthetase is not a part of the lac operon; it is involved in the synthesis of tryptophan and is not regulated by the lac operon repressor.

6. **Conclusion**: The protein that is not regulated by the repressor in the lac operon is **Tryptophan synthetase**.

### Final Answer:
**Tryptophan synthetase**