Which of the following steps in transcription is catalysed by RNA polymerase?

Options

A. Initiation
B. Elongation
C. Termination
D. All of the above

Explanation

To answer the question "Which of the following steps in transcription is catalyzed by RNA polymerase?", we can break down the transcription process into its main steps and identify the role of RNA polymerase in each.

### Step-by-Step Solution:

1. **Understanding Transcription**:
- Transcription is the process by which DNA is converted into messenger RNA (mRNA). This process is crucial for the expression of genes and involves several steps.

2. **Steps of Transcription**:
- The transcription process consists of three main stages: initiation, elongation, and termination.

3. **Initiation**:
- During initiation, the double-stranded DNA unwinds and separates to form a small open complex. This step is crucial for RNA polymerase to access the template strand of DNA.

4. **Elongation**:
- In the elongation phase, RNA polymerase binds to the template strand of DNA. It catalyzes the addition of ribonucleotides to the growing mRNA strand. This is the main function of RNA polymerase during transcription, as it synthesizes the mRNA by adding nucleotides complementary to the DNA template.

5. **Termination**:
- The termination step occurs when RNA polymerase encounters specific termination signals. This signals the end of transcription, and the RNA polymerase releases the newly synthesized mRNA strand. While termination involves RNA polymerase, it is not the primary catalytic action of RNA polymerase but rather a concluding step.

6. **Conclusion**:
- RNA polymerase is involved in all three steps of transcription: initiation, elongation, and termination. However, its primary catalytic function is most prominent during the elongation phase, where it synthesizes the mRNA.

### Final Answer:
The correct answer is **all of the above** (initiation, elongation, and termination) are steps in transcription that involve RNA polymerase.

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