In eukaryotic 5′-capping in m-RNA is required for-
(1) Initiation of transcription
(2) Initiation of translation
(3) Intron removal
(4) Termination of transcription

Role of 5′-Capping in Eukaryotic mRNA

Correct Answer:

(2) Initiation of translation

Detailed Explanation:

The 5′ cap of eukaryotic mRNA is a specially modified nucleotide (7-methylguanosine) added to the 5′ end of the nascent mRNA transcript shortly after transcription begins. This cap plays several critical roles in mRNA metabolism, but its most important function is to facilitate the initiation of translation.

• The 5′ cap protects mRNA from degradation by exonucleases, increasing mRNA stability.

• It aids in nuclear export of the mRNA by interacting with the cap-binding complex.

• Crucially, the 5′ cap is recognized by the eukaryotic translation initiation factor eIF4E, which recruits the ribosome to the mRNA, enabling efficient translation initiation.

• The cap also influences pre-mRNA splicing but is not directly involved in intron removal itself.

• It does not play a role in the initiation or termination of transcription.

Why Other Options Are Incorrect:

1. Initiation of transcription
   The 5′ cap is added after transcription initiation; it does not influence the start of transcription.

2. Intron removal
   While the cap can promote splicing efficiency by interacting with the spliceosome, it is not directly responsible for intron removal.

3. Termination of transcription
   The 5′ cap has no role in transcription termination.

Summary Table

Conclusion

The 5′ cap on eukaryotic mRNA is essential for the initiation of translation, protecting the mRNA from degradation and enabling ribosome binding. This modification ensures efficient protein synthesis from the mature mRNA transcript.