Transcription unit in DNA contains-

Options

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

Answer

To answer the question regarding what a transcription unit in DNA contains, we can break down the components involved in the transcription process.

### Step-by-Step Solution:

1. **Understanding the Transcription Unit**:
- A transcription unit is a segment of DNA that is transcribed into RNA. It includes all the necessary elements for the transcription process to occur.

2. **Components of the Transcription Unit**:
- **Promoter**: This is a specific region of DNA that initiates transcription. It is located at the 5' end of the coding strand and serves as the binding site for RNA polymerase, the enzyme responsible for synthesizing RNA.
- **Structural Gene**: This is the part of the DNA that contains the actual sequence that will be transcribed into RNA. It carries the information that will be translated into a protein.
- **Terminator**: This is a sequence at the end of the transcription unit that signals the termination of transcription. It is located at the 3' end of the coding strand.

3. **Directionality**:
- The transcription process occurs in a specific direction. RNA polymerase synthesizes RNA in the 5' to 3' direction, which means it reads the DNA template strand in the 3' to 5' direction.

4. **Conclusion**:
- Therefore, a transcription unit in DNA contains a promoter, a structural gene, and a terminator. All these components are essential for the transcription process to occur correctly.

### Final Answer:
The transcription unit in DNA contains:
- Promoter
- Structural Gene
- Terminator