During expression of an operon , RNA polymerase binds to

Options

A. structural gene
B. regulator gene
C. operator
D. promoter

Answer

To answer the question "During expression of an operon, RNA polymerase binds to," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Operon Structure**:
- An operon consists of several components: a promoter, an operator, a regulator gene, and structural genes.
- The promoter is the specific region where RNA polymerase binds to initiate transcription.

2. **Identifying the Role of RNA Polymerase**:
- RNA polymerase is the enzyme responsible for synthesizing RNA from a DNA template during transcription.
- It must bind to the promoter region of the operon to begin the transcription process.

3. **Locating the Promoter**:
- The promoter is located upstream of the structural genes in the operon.
- It is a key regulatory sequence that signals where RNA polymerase should attach.

4. **Binding Process**:
- When RNA polymerase binds to the promoter, it unwinds the DNA and begins synthesizing mRNA by reading the template strand of DNA.
- This process leads to the transcription of the structural genes present in the operon.

5. **Conclusion**:
- Therefore, during the expression of an operon, RNA polymerase binds specifically to the promoter region of the operon.

### Final Answer:
RNA polymerase binds to the promoter during the expression of an operon.

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