The presence of which gene in a transcription unit that also defines the template and coding strands

Options

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

Answer

To answer the question regarding which gene in a transcription unit defines both the template and coding strands, we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Understanding the Transcription Unit**:
- A transcription unit consists of several key components: the promoter, structural genes, operator, and regulatory genes. Each of these plays a critical role in the process of transcription.

2. **Identifying the Promoter**:
- The promoter is a specific region of DNA where RNA polymerase binds to initiate transcription. It is crucial for the transcription process as it determines where transcription begins.

3. **Template and Coding Strands**:
- In the context of transcription, the template strand is the DNA strand that is read by RNA polymerase to synthesize mRNA, while the coding strand (also known as the sense strand) has the same sequence as the mRNA (except for the substitution of uracil for thymine).

4. **Role of the Promoter**:
- The promoter is located upstream of the structural genes and is essential for defining both the template and coding strands. It is responsible for the binding of RNA polymerase, which then transcribes the gene into mRNA.

5. **Conclusion**:
- Therefore, the gene that defines both the template and coding strands in a transcription unit is the **promoter**. The presence of the promoter is crucial as it initiates the transcription process and determines the direction of transcription.

### Final Answer:
The presence of the **promoter** gene in a transcription unit defines both the template and coding strands.

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