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Midterm

BIOB11H3 Study Guide - Midterm Guide: Snrnp, Spliceosome, Intron


Department
Biological Sciences
Course Code
BIOB11H3
Professor
Dan Riggs
Study Guide
Midterm

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Lecture 6
consensus sequence: The most common version of a conserved sequence. The TTGACA
sequence of a bacteria promoter (known as the -35 element) is an example of a consensus
sequence.
frameshift: Mutations in which a single base pair is either added to or deleted from the DNA,
resulting in an incorrect reading from from the point of mutation through the reminder of the
coding sequence.
missense mutation: if an insertion or deletion occurs then if it is anything but a multiple of
three then it shifts the code and creates a missense protein so it doesn't work
snRNP (small nuclear ribonuclear protein particle): RNAs required for the mRNA processing
that are small (90 - 300 nucleotides long) and that function in the nucleolus.
spliceosome: a macromolecular complex containing a variety of proteins and a number of
distinct ribonucleoprotein particles that functions in removal of introns. (11.4)
ribozyme (self-splicing RNA): An RNA molecule that functions as a catalyst in a cellular
reactions.
group 1 intron: found in nuclear RNA of lower eukaryotes, and some organelles. Forms
elaborate 3D structure due to intra-strand base-pairing
group 2 intron: found in organelles, also self-splicing, but mechanism generates an
intermediate called a lariat
lariat: loop like structure formed by group 2 introns during transcription
branch point A: a very reactive nucleotide which participates in the cleavage event close to the
three prime exon
magic bullets: can be created to downgrade the overregulation of a specific gene
Suppress what is wrong without affecting anything else is called magic bullet
siRNA: Small (21-23 nucleotide), double stranded fragments formed when double-stranded
RNA initiates the response during RNA silencing.
microRNA: Small RNAs (20-23 nucleotides long) that are synthesized from many sites in the
genome and involved in inhibiting translation or increasing degradation of complementary
mRNAs. (11.5)
Lecture 6 RNA splicing and related phenomena
What happens if things dont go according to plan
Consequences of mis splicing?
1. Accumulation of unspliced dna figure 11-2
If splicing is right then the RNA should be exported to the Cytoplasm where the interact with
ribosomes to be Translated
But if they are not exported then they are usually degraded

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Then no protein is produced
The second thing that can happen is called frameshift
2.Frame shift
This can result in a novel protein
And perhaps containing a protein sequence which is coded by an intron
During an aberrant splicing part of intron 1 still has not been spliced
So if this aberrant protein is transferred to the cytoplasm and translated into a protein and
what you get is a protein which's normal function does not work
The frames are the triplets set of nucleotides which encode the amino acids
If it is anything but a multiple of three then it gets shifted and create a missense protein
Missense protein produced so it doesn't work
A frameshift Results from the addition or deletion of nucleotide To alter the reading frame of
the triplet genetic code
If a frameshift occurs due to misplicing of the entire intron then the beginning of the protein
will be the same but after that intron all of the nucleotide triplets will differ Causing a
missense protein

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In 1982 Tom Cech discovered that RNA that exhibits Self splicing enzymatic activity-called
ribozymes- rna enzyme
There are two types of introns that you called group one Intron and group 2 introns
In the group one Intron's Part of the protein is complementary to self so to can fold onto its self
In group two introns they form something called a lariat
Figure 11 31
The two blue stripes are exons and the red are Introns
There are stems and loops of Introns and the stems are where complementary base pairing
happen
Something important for self splicing RNA is the Structure called branch point A Which is a
very reactive nucleotide which participates in the cleavage event close to the three prime exon.
The elaborate structure of the Intron's strategically align the exons Such that the cleavage
reactions can take place at both the ends and since they are close together they can be ligated
easily.
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