A transcription unit is defined by three regions in DNA as

Options

A. Promoter, terminator and inducer
B. Promoter, structural gene and terminator
C. Inducer, Structural gene and Operator
D. Promoter, Operator and Structural gene

Answer

To answer the question regarding the three regions that define a transcription unit in DNA, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Identify the Components of a Transcription Unit**:
A transcription unit consists of three main regions: the promoter, the coding sequence, and the terminator.

2. **Define the Promoter**:
The promoter is the region of DNA where RNA polymerase binds to initiate transcription. It is located upstream of the coding sequence and is crucial for the start of the transcription process.

3. **Explain the Coding Sequence**:
The coding sequence is the part of the DNA that is transcribed into mRNA. This sequence contains the information that will be translated into a protein. It starts from the point where RNA polymerase begins to synthesize RNA.

4. **Describe the Terminator**:
The terminator is the region of DNA that signals the end of transcription. When RNA polymerase reaches this region, it stops transcription and releases the newly formed mRNA strand.

5. **Summarize the Function of Each Region**:
- **Promoter**: Initiates transcription by binding RNA polymerase.
- **Coding Sequence**: Contains the information for protein synthesis.
- **Terminator**: Signals the end of transcription and releases mRNA.

6. **Conclude with the Importance of These Regions**:
Together, these three regions define the transcription unit and are essential for the proper transcription of genes in DNA.

### Final Answer:
A transcription unit is defined by three regions in DNA:
1. Promoter
2. Coding Sequence
3. Terminator