The poly-A tail is added to which end of eukaryotic mRNA?

The poly-A tail is added to which end of eukaryotic mRNA?

• A. 3' end
• B. 5' end
• C. Both ends
• D. Internal sequence

Answer: (A)

The poly-A tail is added to the 3' end of eukaryotic mRNA. During processing, the pre-mRNA is cleaved downstream of a polyadenylation signal, and then poly(A) polymerase adds a stretch of adenine nucleotides to that 3' end. This tail does not occur at the 5' end, nor in the middle of the molecule. The 5' end receives a cap instead, while the poly-A tail remains at the end. This tail serves important roles: it protects the mRNA from rapid degradation, assists in exporting the transcript from the nucleus, and enhances translation efficiency by promoting binding of proteins that help recruit ribosomes.

The poly-A tail is added to the 3' end of eukaryotic mRNA. During processing, the pre-mRNA is cleaved downstream of a polyadenylation signal, and then poly(A) polymerase adds a stretch of adenine nucleotides to that 3' end. This tail does not occur at the 5' end, nor in the middle of the molecule. The 5' end receives a cap instead, while the poly-A tail remains at the end.

This tail serves important roles: it protects the mRNA from rapid degradation, assists in exporting the transcript from the nucleus, and enhances translation efficiency by promoting binding of proteins that help recruit ribosomes.