The lac operon consists of

Options

A. Four regulatory genes only
B. One regulatory gene and three structural genes
C. Two regulatory genes and two structural genes
D. Three regulatory genes and three structural genes

Answer

**Step-by-Step Solution:**

1. **Understanding the Lac Operon**: The lac operon is a genetic regulatory system found in prokaryotes, particularly in E. coli. It is responsible for the metabolism of lactose.

2. **Components of the Lac Operon**: The lac operon consists of several key components:
- **Regulatory Gene**: This gene produces a repressor protein that can bind to the operator region and inhibit transcription.
- **Promoter**: This is the region where RNA polymerase binds to initiate transcription of the structural genes.
- **Operator**: This is the segment of DNA that the repressor binds to, blocking RNA polymerase from transcribing the structural genes.
- **Structural Genes**: There are three structural genes in the lac operon:
- **lacZ**: Codes for beta-galactosidase, which breaks down lactose into glucose and galactose.
- **lacY**: Codes for permease, which facilitates the entry of lactose into the cell.
- **lacA**: Codes for transacetylase, which is involved in the metabolism of lactose.

3. **Counting the Genes**:
- **Regulatory Gene**: 1
- **Promoter**: 1
- **Operator**: 1
- **Structural Genes**: 3 (lacZ, lacY, lacA)

4. **Total Components**:
- Total = 1 (regulatory) + 1 (promoter) + 1 (operator) + 3 (structural) = 6 components in total, but the question specifically asks for the number of regulatory and structural genes.
- Regulatory Genes = 1
- Structural Genes = 3

5. **Conclusion**: Based on the components of the lac operon, the correct answer is that it consists of 1 regulatory gene and 3 structural genes.

**Final Answer**: The lac operon consists of 1 regulatory gene and 3 structural genes.

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