Transcription and processing of eukaryotic genes - part 2

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Two important steps following transcription
Modification of the ends. and removal of introns.
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What end gets polyadenylated?
The 3' end. The 5' end gets capped.
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Why are both these things important?
The cell can tell if both ends are present and therefore the mrna is intact before it exports it from the nucleus
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What does poly-adenylation result in?
stabilisation, longer half life, nuclear export, and it's involved in translation
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In polyadenylation - What binds to the polyA signal?
CPSF - cleavage and poly-adenylation specificity factor.
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What additional proteins bind?
CstF cleavage stimulatory factor. Cleavage factors 1 and 2.
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What binds next to the complex
PAP - poly A polymerase.
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Where does cleavage take place?
10-35nt upstream of the polyA signal
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What happens after cleavage?
the free 3' end is slowly polyadenylated. the cleavage factors are released along with the downstream cleavage product
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How does rapid polyadenylation take place
Multiple copies of PABII bind to the short A tail, which accelerates the rate of addition by PAP.
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When does polyadenlyation stop? How?
after 200-250 residues have been added. PABII signals PAP to stop polymerisation
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Splicing- when is RNA correctly termed mRNA
After splicing and 5'/3' capping has taken place.
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In the first step in spilcing, what associates with pre-mRNA
u1 and u2 snRNPs
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What then joins and what do they form?
U4, U5 and U6. This forms the spliceosome
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How many other protiens are involved in making the spliceosome
at least 50
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What converts the spliceosome into a catalytically active conformation?
Re-arrangement of base pairs between snRNAs.
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What happens after it becomes catalytically acitve?
U1 and U4 are destablished and released
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Which two make the catalytic core
U2 and U6.
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What does the catalytic core do?
Catalyses the first transestierification reaction, forming and intermediate 2'-5' phosphodiester bond
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When does the 2nd transesterification reaction occur?
Following further rearrangements between the snRNPS.
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What is the result of the 2nd transesterification bond?
the two exons are joined by a standard 3' - 5' phosphodiester bond.
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What happens to the intron
It's released as a lariat structure
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What happens to the latriat structure?
converted into linear RNA by a debranching enzyme
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What is the main mechanism for regulating mRNA processing?
Alternative splicing
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what comprise >98% of splice junctions in the human genome
GU-AG introns
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Example of differential splicing to produce differential protiens
fibronectin, Dxl in drosophila
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What is fibronectin?
A long adhesive multi-domain protien secreted from the cell
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How big is the gene
75 kb with multiple exons
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Where are two places where fibronectin is expressed differently
in the liver and fibroblasts
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What does fibronectin in the liver do?
secreted into the blood and circulates, it contains fibrin binding domains which can bind fibrin during blood cots and allows platelets to stick
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What does fibronectin in the fibroblasts do?
adheres fibroblasts to the ECM
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Which two exons are removed in the liver form - but are present in the fibroblast form
EIIB and EIIA
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How many other types of fibronectin have been described?
over 20
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What is the first gene to act in the cascade that regualates sexual differention in drosophila
Sxl protein
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What transcribes Sxl?
A promotor that is only active in females early in development
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What happens to this promoter later in development
its shut off and a different promotor becomes active in males and females
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What happens in males?
The absence of the SXL protein leads to pre-mrna being spliced to include exon 3 and becoming non-functional
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How does Sxl create a functional protein>?
Promotes the removal of exon 3.
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What else does the sxl protein regulate
splicing of the transformer gene mRNA.
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How does this differ in males and females
males have no functional sxl protein, so no fucntional tra is produced. in females, sxl proteins binds to 3' end of the intron between ex1 and ex2 - blocks binding of U2AF. Ex1 spliced to a farther 3'site = functional
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What does the tra protien do?
regulates splicing of the double sex gene, which ends up different in males and females.
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What is the male dsx
a transcriptional repressor of genes required for female development
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what is the female dsx
a transcriptional repressor of genes required for female development
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What two protiens does tra act with
rbp1 and rbp2
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U1A
yeah
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an example of 2 proteins encoded by rna editing
the apo-B gene. Apo-B100 in hepatocytes, Apo-b48 in intestinal epithelial cells
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Card 2

Front

What end gets polyadenylated?

Back

The 3' end. The 5' end gets capped.

Card 3

Front

Why are both these things important?

Back

Preview of the front of card 3

Card 4

Front

What does poly-adenylation result in?

Back

Preview of the front of card 4

Card 5

Front

In polyadenylation - What binds to the polyA signal?

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Preview of the front of card 5
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