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 option provided in the context of the lac operon.

### Step-by-Step Solution:

1. **Understand the Operon Concept**:
- An operon is a segment of DNA that contains structural genes and regulatory elements. It consists of genes that code for proteins involved in a particular metabolic pathway.

2. **Identify the Components of the Lac Operon**:
- The lac operon includes:
- **I gene**: Codes for the repressor protein.
- **P gene**: Promoter region where RNA polymerase binds.
- **O gene**: Operator region where the repressor binds.
- **Z, Y, A genes**: Structural genes that code for enzymes (Z for beta-galactosidase, Y for lactose permease, and A for transacetylase).

3. **Analyze Each Option**:
- **Option 1**: "The sequence of structural gene in lac operon is ZyA."
- This is correct because the order is indeed Z, Y, A.
- **Option 2**: "Allolactose turns it on by binding with the repressor."
- This is correct as allolactose binds to the repressor, inactivating it and allowing transcription.
- **Option 3**: "It is an inducible operon."
- This is also correct since the lac operon is induced by the presence of lactose or allolactose.
- **Option 4**: "The operator gene receives RNA polymerase to switch it off."
- This is incorrect. The operator does not bind RNA polymerase; instead, it binds the repressor protein. RNA polymerase binds to the promoter region.

4. **Conclusion**:
- The incorrect statement is **Option 4**. The operator region does not receive RNA polymerase; it is the promoter region that binds RNA polymerase.

### Final Answer:
The incorrect statement regarding the operon concept is **Option 4**: "The operator gene receives RNA polymerase to switch it off."