Which is incorrect

Options

A. i-gene codes for the repressor of lac operon
B. z-gene codes for the beta-galactosidase
C. y-gene codes for transacetylase
D. three gene products are required for metabolism of lactose

Answer

To determine which statements about the lac operon are incorrect, we will analyze each gene and its function systematically.

### Step 1: Evaluate the I gene
- The **I gene** is responsible for coding a repressor protein that inhibits the expression of the operon when lactose is not present.
- **Conclusion**: The statement "I gene codes for the repressor of the lac operon" is **true**.

### Step 2: Evaluate the Z gene
- The **Z gene** codes for **beta-galactosidase**, an enzyme that breaks down lactose into glucose and galactose.
- **Conclusion**: The statement "Z gene codes for beta-galactosidase" is **true**.

### Step 3: Evaluate the Y gene
- The **Y gene** codes for **lac permease**, which facilitates the transport of lactose into the bacterial cell.
- The statement that "Y gene codes for transacetylase" is **false**. The **A gene** is responsible for coding transacetylase.
- **Conclusion**: The statement "Y gene codes for transacetylase" is **false**.

### Step 4: Evaluate the A gene
- The **A gene** does indeed code for **transacetylase**.
- **Conclusion**: The statement "A gene codes for transacetylase" is **true**.

### Step 5: Evaluate the requirement of gene products for lactose metabolism
- The statement "three gene products are required for the metabolism of lactose" is misleading. While all three genes (Z, Y, and A) play roles in lactose metabolism, it is primarily the **Z gene** that is crucial for the breakdown of lactose. The Y and A genes assist in the process but are not strictly required for the metabolism itself.
- **Conclusion**: The statement "only one gene is required for the metabolism" is **true** in a strict sense, but all three genes contribute to the overall process.

### Final Summary
- The incorrect statements are:
1. "I gene codes for the repressor of the lac operon" - **True**
2. "Z gene codes for beta-galactosidase" - **True**
3. "Y gene codes for transacetylase" - **False**
4. "Three gene products are required for the metabolism of lactose" - **False** (misleading)