During mRNA processing, the 5' cap and 3' poly-A tail are added before intron removal.

During mRNA processing, the 5' cap and 3' poly-A tail are added before intron removal.

• A. False
• B. True
• C. Not specified
• D. Always after splicing

Answer: (B)

The key idea here is how mRNA is matured in the nucleus. The 5' cap is added very early, essentially as soon as the transcript starts being made, and it protects the 5' end and helps ribosomes recognize the mRNA. The 3' poly-A tail is added later, after transcription finishes and the pre-mRNA is cleaved at the polyadenylation site; this tail helps stabilize the molecule and aids export from the nucleus. Intron removal (splicing) is another processing step that occurs during maturation and can overlap with capping and tailing, but the cap and tail are already in place as part of the maturation process before the message is exported. Therefore, describing the cap and poly-A tail as being added before intron removal aligns with how these processing events are coordinated in many cellular contexts.

The key idea here is how mRNA is matured in the nucleus. The 5' cap is added very early, essentially as soon as the transcript starts being made, and it protects the 5' end and helps ribosomes recognize the mRNA. The 3' poly-A tail is added later, after transcription finishes and the pre-mRNA is cleaved at the polyadenylation site; this tail helps stabilize the molecule and aids export from the nucleus. Intron removal (splicing) is another processing step that occurs during maturation and can overlap with capping and tailing, but the cap and tail are already in place as part of the maturation process before the message is exported. Therefore, describing the cap and poly-A tail as being added before intron removal aligns with how these processing events are coordinated in many cellular contexts.