In eukaryotes, the process of processing of primary transcript involves

Options

A. removal of introns
B. capping at 5' end
C. tailing (polyadenylation) at 3' end
D. all of these.

Explanation

To answer the question regarding the processing of primary transcripts in eukaryotes, we will break down the steps involved in this process.

### Step-by-Step Solution:

1. **Understanding Primary Transcript**:
- In eukaryotic cells, the primary transcript is initially synthesized as heterogeneous nuclear RNA (hnRNA), which contains both coding (exons) and non-coding (introns) sequences.

2. **Removal of Introns (Splicing)**:
- The first step in processing the primary transcript is the removal of introns. This process is known as splicing. During splicing, the introns are cut out from the hnRNA, and the exons are joined together to form a continuous coding sequence.

3. **Capping at the 5' End**:
- The next step is the addition of a 5' cap to the primary transcript. This cap is a modified guanine nucleotide (7-methylguanylate) that protects the mRNA from degradation and assists in ribosome binding during translation.

4. **Tailing at the 3' End**:
- Following capping, a poly-A tail is added to the 3' end of the mRNA. This tail consists of a long chain of adenine nucleotides (adenylate residues) and serves to stabilize the mRNA and facilitate its export from the nucleus.

5. **Final Process**:
- After splicing, capping, and tailing, the processed mRNA is now ready to be transported out of the nucleus and translated into a protein.

### Conclusion:
- Therefore, the processing of the primary transcript in eukaryotes involves the removal of introns (splicing), capping at the 5' end, and tailing at the 3' end. Thus, the correct answer is that all of these processes are involved.

### Final Answer:
- The processing of primary transcript in eukaryotes involves: **removal of introns (splicing), capping at the 5' end, tailing at the 3' end, and all of these processes.**

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