Select the correct statement regarding post-transcriptional modification.

Options

A. In capping, methyl guanosine triphosphate is added at the 3' end.
B. In tailing, adenylate residues (200- 300) are added at 3'-end in a template- dependent manner.
C. It is a process of conversion of mRNA to hnRNA.
D. It involves removal of introns and joining of exons.

Answer

To solve the question regarding post-transcriptional modification, let's analyze each option step by step:

### Step-by-Step Solution:

1. **Understanding Post-Transcriptional Modification**:
- Post-transcriptional modification refers to the processes that occur to the pre-mRNA (also known as hnRNA) after it is synthesized from DNA but before it is translated into a protein.

2. **Analyzing the Options**:
- **Option 1**: "In capping methyl guanosine triphosphate is added at the 3 prime end."
- This statement is incorrect. The 7-methyl guanosine cap is added at the 5' end, not the 3' end.

- **Option 2**: "In tailing adenylate residues are added at the 3 prime end in a template-dependent manner."
- This statement is also incorrect. The addition of adenylate residues (polyadenylation) occurs at the 3' end in a template-independent manner.

- **Option 3**: "It is a process of conversion of mRNA to hnRNA."
- This statement is incorrect. The process is actually the conversion of hnRNA to mature mRNA, not the other way around.

- **Option 4**: "It involves the removal of introns and joining of exons."
- This statement is correct. During post-transcriptional modification, introns are removed through a process called splicing, and exons are joined together to form mature mRNA.

3. **Conclusion**:
- The correct statement regarding post-transcriptional modification is **Option 4**: "It involves the removal of introns and joining of exons."