Which of the following is incorrect for operon concept?

Options

A. The sequence of structural gene in lac operon is ZYA where Z gene codes for hydrolytiv enzyme
B. Allolactose turns it on by binding with repressor protein
C. It is an inducible operon and controls catabolic reactions
D. Operator gene receives RNA polymerase to switch it off

Answer

To solve the question regarding the incorrect statement about the operon concept, we will analyze each of the provided options based on the information about the lac operon.

### Step-by-Step Solution:

1. **Understanding the Operon Concept**:
- The operon concept is a regulatory mechanism in prokaryotic cells (like bacteria) that controls the expression of genes. It consists of structural genes, a promoter, an operator, and regulatory genes.

2. **Identifying Components of the Lac Operon**:
- The lac operon consists of three structural genes: Z, Y, and A.
- The promoter is the site where RNA polymerase binds to initiate transcription.
- The operator is the site where the repressor protein binds to inhibit transcription.
- The regulatory gene (I) produces the repressor protein.

3. **Analyzing the Function of the Lac Operon**:
- When lactose (inducer) is absent, the repressor binds to the operator, preventing RNA polymerase from transcribing the structural genes.
- When lactose is present, it binds to the repressor, inactivating it. The repressor then cannot bind to the operator, allowing RNA polymerase to transcribe the structural genes.

4. **Evaluating Each Statement**:
- **Statement 1**: The sequence of structural genes in the lac operon is ZYA. This is correct.
- **Statement 2**: Allo-lactose (a form of lactose) binds to the repressor and activates the lac operon. This is correct.
- **Statement 3**: The lac operon is an inducible operon that controls catabolic reactions. This is correct.
- **Statement 4**: The operator gene receives RNA polymerase to switch it off. This is incorrect because the operator is where the repressor binds, not RNA polymerase.

5. **Conclusion**:
- The incorrect statement regarding the operon concept is option number 4.

### Final Answer:
The incorrect statement for the operon concept is: **"Operator gene receives RNA polymerase to switch it off."**

---