Which of the following is not a transcription unit of the DNA ?

Options

A. Terminator
B. Promoter
C. Organiser
D. Structural gene

Answer

To determine which of the following is not a transcription unit of DNA, we first need to understand the components of a transcription unit. A transcription unit consists of several key parts:

1. **Promoter Region**: This is the region where RNA polymerase binds to initiate transcription. It is located upstream of the coding sequence.

2. **Structural Gene**: This is the part of the DNA that is transcribed into RNA. It contains the coding sequence that will be translated into a protein.

3. **Terminator Region**: This is the sequence that signals the end of transcription. It is where RNA polymerase stops synthesizing RNA.

4. **Coding Strand and Template Strand**: The coding strand is the DNA strand that has the same sequence as the RNA (except for thymine being replaced by uracil), while the template strand is the one that RNA polymerase uses to synthesize the RNA.

Now, let's analyze the options provided in the question. We need to identify which component is not part of a transcription unit.

- **Promoter**: This is indeed a transcription unit.
- **Structural Gene**: This is also part of a transcription unit.
- **Terminator**: This is a necessary component of a transcription unit.
- **Organizer**: This term does not refer to any recognized component of a transcription unit in DNA.

Based on this analysis, the component that is not a transcription unit of DNA is the **Organizer**.

### Step-by-Step Solution:
1. Identify the components of a transcription unit: promoter, structural gene, and terminator.
2. Understand the roles of each component in the transcription process.
3. Analyze the options given in the question.
4. Determine that the "Organizer" is not a recognized component of a transcription unit.
5. Conclude that the correct answer is **Organizer**.