Which of the following events take place during post - transcriptional modification in eukaryotes ?

Options

A. Exons are removed from primary transcript.
B. 7 - methyl gunosine cap is added at 3' end of RNA transcript
C. Addition of poly A segment at 5' end of transcript .
D. In tailing , adenylated residues are added in a template independent manner.

Answer

### Step-by-Step Solution:

1. **Understanding Post-Transcriptional Modification**:
- Post-transcriptional modification refers to the processes that occur to the RNA transcript after it has been synthesized but before it is translated into a protein. This is a crucial step in eukaryotic gene expression.

2. **Identifying Key Processes**:
- In eukaryotes, several key modifications occur during this phase:
- **Splicing**: This is the process where introns (non-coding regions) are removed from the primary RNA transcript, and exons (coding regions) are joined together. This results in a mature mRNA molecule.
- **Capping**: A 7-methylguanosine cap is added to the 5' end of the RNA transcript. This cap is important for mRNA stability and initiation of translation.
- **Polyadenylation**: A poly A tail (a sequence of adenine nucleotides) is added to the 3' end of the RNA transcript. This process is known as tailing and enhances the stability of the mRNA and aids in its export from the nucleus.

3. **Analyzing the Options**:
- The question provides several options regarding events that take place during post-transcriptional modification. We need to evaluate each option based on our understanding of the processes involved.

4. **Evaluating Each Statement**:
- **Option 1**: "Introns are removed from the primary transcript."
- This is true and refers to splicing.
- **Option 2**: "7-methylguanosine cap is added at the 3' end of the RNA transcript."
- This is false; the cap is added at the 5' end.
- **Option 3**: "Addition of poly A segment at the 5' end of transcript."
- This is false; the poly A tail is added at the 3' end.
- **Option 4**: "Adenylated residues are added in a template-independent manner."
- This is true and refers to the process of polyadenylation.

5. **Conclusion**:
- The correct events that take place during post-transcriptional modification in eukaryotes include splicing (removal of introns), the addition of a 7-methylguanosine cap at the 5' end, and the addition of a poly A tail at the 3' end in a template-independent manner.

### Final Answer:
The correct events that take place during post-transcriptional modification in eukaryotes are:
- Introns are removed from the primary transcript (splicing).
- A 7-methylguanosine cap is added at the 5' end.
- A poly A tail is added at the 3' end in a template-independent manner.