alleryStart learning →Why must every intron be removed with single-nucleotide accuracy?
AAn error would leave the transcript uncapped
BAn error would shift the frame of joined exons
CAn error would block export from the nucleus
DAn error would shorten the poly-A tail added
Answer & Solution
Correct answer: B. An error would shift the frame of joined exons
1. Translation reads the joined exons as consecutive triplets from the start codon onward.
2. An error of even one nucleotide shifts the reading frame of the rejoined exons.
3. Every amino acid after the junction is then mis-specified and the protein comes out dysfunctional.
4. Splicing accuracy is enforced by a sequence-specific mechanism precisely because of this sensitivity.
5. Capping happens at the 5' end while the transcript is still being made, so a splicing slip cannot undo it.
6. Tail length is set by poly-A polymerase and is independent of where the exons were joined.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 15 "Genes and Proteins", section 15.4 RNA Processing in Eukaryotes_
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