Biology / Unit 6 Bio 1273 short lesson, about 20 seconds
The Poly-A Tail
Captions available
The idea
A eukaryotic pre-mRNA's 3' end receives a poly-A tail, roughly 200 adenine nucleotides added after the RNA is cleaved at a specific site.
In practice
An enzyme adds a long run of adenine nucleotides to the pre-mRNA's cleaved 3' end, forming the poly-A tail.
Where people slip
The poly-A tail is added after transcription and cleavage, distinct from the 5' cap added near transcription's start.
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