Capping in hnRNA is catalysed by

Options

A. Poly A polymerase
B. SnRNA
C. Guanyl transferase
D. Catalytic RNA

Answer

To answer the question "Capping in hnRNA is catalysed by," we need to analyze the options provided and understand the role of each enzyme mentioned. Here’s a step-by-step breakdown of the solution:

### Step 1: Understanding hnRNA
- Heterogeneous nuclear RNA (hnRNA) is the precursor to mRNA and undergoes several modifications before it becomes mature mRNA. One of these modifications is capping.

### Step 2: Identifying the Capping Process
- Capping refers to the addition of a modified guanine nucleotide at the 5' end of the hnRNA. This cap protects the RNA from degradation and is important for translation.

### Step 3: Evaluating the Options
1. **Polymerase**:
- This enzyme is involved in the transcription process and adds nucleotides to the growing RNA strand. However, it does not catalyze the capping of hnRNA.
- **Hint**: Remember that polymerases are primarily responsible for synthesizing RNA from a DNA template.

2. **SNRNA (Small Nuclear RNA)**:
- SNRNA is involved in the splicing of introns from the pre-mRNA but does not play a direct role in the capping process.
- **Hint**: SNRNA is crucial for processing RNA but is not the enzyme that adds the cap.

3. **Guanosine Transferase**:
- This enzyme is responsible for the capping of hnRNA. It catalyzes the addition of the guanine cap to the 5' end of the RNA molecule.
- **Hint**: Look for enzymes that specifically modify the 5' end of RNA for capping.

4. **Catalytic RNA**:
- Catalytic RNA, often referred to as ribozymes, can catalyze certain biochemical reactions but is not involved in the capping of hnRNA.
- **Hint**: Catalytic RNAs are more about catalyzing reactions rather than modifying RNA structures like capping.

### Step 4: Conclusion
- After evaluating all the options, the correct answer to the question "Capping in hnRNA is catalysed by" is **Guanosine Transferase**.

### Final Answer
Capping in hnRNA is catalysed by **Guanosine Transferase**.