Select incorrectly matched pair

Options

A. Lac z - Constitutive gene
B. Operatorgene - Smallest gene of lac operon
C. Lac a - Transacaetylase
D. Promotor gene- RNA polymerase

Answer

To solve the question of selecting the incorrectly matched pair regarding the lac operon, we can break down the information step by step:

### Step-by-Step Solution:

1. **Understanding the Lac Operon**:
- The lac operon consists of genes that are involved in the metabolism of lactose. It includes structural genes (Z, Y, A) and regulatory genes (I, P, O).

2. **Identifying the Genes**:
- **lacZ**: This gene codes for β-galactosidase, which is involved in breaking down lactose.
- **lacY**: This gene codes for permease, which facilitates the entry of lactose into the cell.
- **lacA**: This gene codes for transacetylase, which is involved in the metabolism of lactose, though its exact function is not fully understood.
- **I**: This is the regulatory gene that codes for the repressor protein.

3. **Analyzing the Pairs**:
- The first pair states that **lacZ is a constitutive gene**. This is incorrect because lacZ is not constitutive; it is regulated and expressed only when lactose is present.
- The second pair states that **the operator is the smallest gene of the lac operon**. This is correct as the operator is a short sequence of DNA.
- The third pair states that **lacA codes for transacetylase**. This is also correct.
- The fourth pair states that **the promoter gene is where RNA polymerase binds**. This is correct.

4. **Conclusion**:
- The incorrectly matched pair is the first one: **lacZ is a constitutive gene**. This statement is false as lacZ is regulated and not constitutive.

### Final Answer:
The incorrectly matched pair is: **lacZ is a constitutive gene**.

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