In eukaryotic mRNA processing, the 5' cap added co-transcriptionally is composed of:

• A Adenosine connected by a standard 3'-5' phosphodiester bond
• B 7-methylguanosine connected by a 5'-5' triphosphate linkage ✓
• C Cytidine connected by a 2'-5' phosphodiester bond
• D Guanosine connected by a 3'-5' triphosphate linkage

Explanation

The 5' cap is a 7-methylguanosine (m7G) residue added by guanylyl transferase via an unusual 5'-5' triphosphate bridge to the first transcribed nucleotide, which is also subsequently methylated at the 2' position. This unique linkage protects the mRNA from 5'-exonuclease degradation, facilitates nuclear export, is recognized by eIF4E during cap-dependent translation initiation, and marks the mRNA as 'self' for the innate immune system.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.