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Lecture 6

BIOB11H3 Lecture Notes - Lecture 6: Rna Interference, Intron, Missense Mutation

Biological Sciences
Course Code
Dan Riggs

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LECTURE 6: RNA splicing, catalytic RNAs and RNA interference Part 1
SP 11.30- nucleotide sequences at splice sites of pre-mRNAs.
A pre-mRNA contains info that directs the machinery responsible for RNA splicing. The
nucleotide sequences shown in the regions of the splice sites are based on analysis of a large
number of pre-mRNAs = referred to as consensus sequences*
o Consensus Sequences are at splice junctions (points on a DNA sequence at which unnecessary
DNA is removed during the process of protein creation)
o Accurate splicing removes intron, so adjacent exons are joined to form a contiguous
coding sequence
What are the consequences of mis-splicing?
1. Accumulation of unspliced RNAs
Not exported to the cytoplasm, so likely degraded
No protein produced
2. Frameshift* resulting in a new/unusually interesting protein (maybe containing part
of an intron)
Fraeshift: additio/deletio of uleotides to hage the readig frae of the triplet geeti ode
Intron not spliced out precisely in
picture. When translated, makes aberrant
protein (has xtra amino acids- changes
structure, and potentially it’s function).
Triplet set of nucleotides encode each of these xtra amino acids
Missense protei produed… oral futio of protei ay e lost!
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Example: 1st sequence
shows normal splicing of
pre-mRNA (intron in red
completely taken out).
2nd sequence is mis-sense
protein… futio of this
protein may be lost
1982: To Ceh disovers self-spliig RNA in the organism Tetrahymena
some vocab that Cech coined…
1. Ribozyme: an RNA that has enzymatic activity
2. Group I introns: found in nuclear RNA of lower eukaryotes, some organelles
Forms elaborate 3D structure due to intra-strand/complimentary base-pairing
3. Group II introns: found in organelles, also self-splicing, but mechanism generates an
intermediate called a lariat.
SP 11.31- The structure and self-splicing pathway of group 2 introns
A) B)
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