Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyeasymcq1 pt

Which statement describes how a eukaryotic mRNA receives its poly(A) tail and what the tail achieves?

A.After the transcript is cleaved beyond a polyadenylation signal, polymerase adds many adenosines that guard the 3' end from degradation
B.Ribosomes assemble the tail from spare ATP molecules after finishing translation
C.Spliceosomes insert adenines between exons while excising each intron from the pre-mRNA
D.RNA polymerase II reads a stretch of T's in the gene, copying adenines directly into the transcript

Explanation

Core Concept

Once cleavage exposes a fresh 3' end downstream of the AAUAAA-type signal, poly(A) polymerase strings on roughly 100 to 250 adenines without any template. The tail slows 3' exonucleases, lengthening the message's lifespan. It also assists nuclear export and efficient translation initiation.

Correct Answer

AAfter the transcript is cleaved beyond a polyadenylation signal, polymerase adds many adenosines that guard the 3' end from degradation

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