Biology, Eighth Edition (Raven)

Chapter 15: Genes and How They Work

How Spliceosomes Process RNA

What is the purpose of introns? DNA is composed of sections known as exons and introns. The exons are the portions that eventually exit the nucleus in the form of mRNA and are used in translation. The introns are removed from the mRNA shortly after transcription. There are a number of hypotheses about the function of introns. One hypothesis is that alternative splicing may allow a single gene to code for more than one version of a protein. In other words a piece of the gene may be an intron in one case and an exon in another case. Another possible explanation is that each exon codes for a module of a protein. Spatially separating the exons may allow for the evolution of proteins by removing, adding, or replacing entire modules.

View the animation below, then complete the quiz to test your knowledge of the concept.



1.

The snRNPs are also called
A)smurfs.
B)snurps.
C)snores.
D)snippets.
E)splits.
2.

Which of the following do snRNPs bind to?
A)exon only
B)exon and the 5' end of the intron
C)5' end of the intron only
D)3' end of the intron only
E)5' and 3' ends of the intron
3.

Which of the following statements about RNA splicing is FALSE?
A)it removes the introns
B)it is performed by the spliceosome
C)it shortens the RNA molecule
D)it always occurs in the nucleus
E)all of the above statements are true
4.

The cutting out of the intron involves the formation of a loop in the mRNA.
A)True
B)False
5.

Only a few eukaryotic genes contain introns.
A)True
B)False
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