Which one of the following is not a part of transcription unit in DNA?

Options

A. The inducer
B. A terminator
C. A promoter
D. The structural gene

Explanation

To solve the question "Which one of the following is not a part of transcription unit in DNA?", we need to understand the components of a transcription unit.

### Step-by-Step Solution:

1. **Understanding the Transcription Unit**:
- A transcription unit is a segment of DNA that is transcribed into RNA. It consists of specific regions that are essential for the transcription process.

2. **Identifying Components**:
- The transcription unit typically includes three main components:
- **Promoter**: This is the region where RNA polymerase binds to initiate transcription.
- **Structural Gene**: This is the coding region that gets transcribed into mRNA.
- **Terminator**: This is the sequence that signals the end of transcription.

3. **Analyzing the Options**:
- Now, let's look at the options provided:
- A. Inducer
- B. Terminator
- C. Promoter
- D. Structural Gene

4. **Determining the Incorrect Option**:
- Among the options, the **inducer** is not a part of the transcription unit. Inducers are molecules that can enhance the transcription of a gene but are not structural components of the transcription unit itself.

5. **Conclusion**:
- Therefore, the correct answer to the question is **A. Inducer**, as it is not a part of the transcription unit in DNA.