During eukaryotic mRNA processing, which modification prevents exonuclease degradation of the 5' end of pre-mRNA?

• A Polyadenylation (poly-A tail addition)
• B Splicing of introns
• C AAUAAA polyadenylation signal recognition
• D 7-methylguanosine 5' cap (m7G cap) ✓

Explanation

The 7-methylguanosine (m7G) cap is added co-transcriptionally to the 5' end of pre-mRNA via an unusual 5'-to-5' triphosphate linkage. It protects the mRNA from 5'-exonuclease degradation, facilitates nuclear export, and is recognised by eIF4E (eukaryotic initiation factor) for ribosome recruitment during translation initiation. Poly-A tail at the 3' end protects from 3' exonucleases and aids in mRNA stability and nuclear export. Splicing removes introns but does not directly protect the 5' end.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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