BIOL253 - L14

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  • Created by: Katherine
  • Created on: 21-04-17 11:20
Can you get transcription of DNA 1000s of base pairs away from the transcriptional start site?
Yes - In eukaryotes
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What do Enhancer regions contain?
A high density of DNA binding sites
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How do enhancer sequences regulate transcription?
By bending DNA
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What does the transcription factor do?
Recruits other proteins
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What forms the nucleosome?
DNA is wrapped by histone octamer
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What are the changes to the histone called?
Epigenetic effects
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What are histones with low levels of acetylation called?
Hypoacetylation
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What happens when histone is deacetylated?
You get a chemical change - you introduce a negative charge which introduces electrostatic effects in the DNA, The histone tails don't bind as tightly to the DNA, and you don' get the constraining of the wrapping around the nucleosome.
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What is the the other effect of histone acetylation?
It induces a landing platform for particular proteins called bromodomain proteins. The acetylgroup is recognised by the proteins and these can in turn recruit other proteins.
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What are the two ways that acetylation can turn on gene expression
Making a looser structure and by activily recruiting these bromodomain proteins
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Binding sites for transcription factors can be inacessible...how?
As they are wrapped around nucleosomes
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What uses ATP to move the histone otctomer?
Chromatin remodelling complexes (SWI/SNF). They an be recruited either sequence specifically (a) or by histone modification (b)
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How does methylation affect the chromatin structure?
It makes it more densely packaged
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What can changes in methylation pattern result in?
Fragile X syndrome, cander, aging
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Deacetylation is associated with...
Transcriptional silecning
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How does RNA pol 2 recognise the site of transcription, it needs
The function of general transcription factors
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RNA pol II requires the presence of general transcriptio factors (e.g. TFIID) to bind to the promoter. It also requires..
The mediator complex, which consists of approximately 20 proteins and is 1MDA in size
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Without the mediator, the more activator they were putting in, the less transcription was occuring..why
Due to squelching - it was binding to something else and therefore it's function was not carried out
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What does mediator do?
It interacts with other transcription factors - mediatees the interacton between RNA polymerase 2 and our transcription factors - it brings them together.
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What is ELK1?
A transcription factor that drives the expression of genes associated with proliferation.
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Proliferation is only driven by ...
Growth factors binding to their receptors
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In the absence of mitogen, what happens to ELK 1?
It binds to SRF (serum response factor) but doesn't activate transcription
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In the presence of mitogens, what whappens?
Mitogen activated signal transduction pathways phosphorylate ELK1. The phosphorylated protein recruits mediator, promoting transcription.
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What happens when you have glucose in E.coli?
Catabolitite repression - genes transcribing galactose are turned off
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What happens when you have galactose present and glucose absent?
Rapid transcription - glucose exerts catabolite repression
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What is the regulatory protein for E.coli?
GAL4 - It activates transcription by binding to the UASg sequence
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Why can't Gal4 activate transcription in the absence of galactose?
Because gal80 binds to Gal4, preventing transcription.
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How does transcription occur when Galactose is present?
Gal3 binds to Gal80, preventing it from binding to Gal4. This allows Gal4 to recruit SAGA and Mediator which activates transcription
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Ligand binding to a nuclear receptor protein leads to...
A conformational change that allows them to drive transcription
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How is the nuclear receptor protein kept out of the nucleus?
It binds to Hsp90 which keeps it in the cytoplasm
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What does Ume6 do?
Regulates transcription in yeast - it responds to particular nutritional cues and can activate or repress transcription.
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What happens when there is enough N and C in the cell? What does Ume6 do?
It binds DNA and recruits co-repressors (Sin3,Rpd3 and Isw2).
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What is Rpd3?
A histone deacetylase
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What is Isw2?
It is a nucleosome remodeling enzyme
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What happens to Ume6 in the absence of N and C?
It is phosphorylated. Sin3 and Rpd3 dissociate and a co-activator, Ime1 is recruited.
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What is a type of regulation of transcription that occurs after transcription?
In many genes, RNA pol 2 stalls after 50bp are transcribed (promoter proximal pausing) and promotedby negative elongation factors (e.g NELF and DSIF). Relief of this pausing allows transcriptional elongation to proceed (allowing cells to respond quic
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Give an example of where promoter proximal pausing occurs?
The gene that encodes Drosophila Hsp70 protein, a chaperone that protects cells from high temeratures
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What is hsp70?
It is a chaperone protein that allows the cells to be able to respond to heat stress - it's important that organisms can respond quickly to heat stress.
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What happens in the absence of heat stress?
GAGA transcription factor binds and recruits NURF. NURF alters the structure of chromatin exposing the control elements. Negative elongation factors (NELF and DSIF) prevent the phosphorylation of the Rpb1 CTD.
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What happens when heat shock occurs?
If temperature rises, Hsf proteins form a trimer. The trimer binds to the HSE sequence. It interacts with mediator to recruit a kinase and the CTD is then phosphorylated, relieving pausing.
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Other cards in this set

Card 2

Front

What do Enhancer regions contain?

Back

A high density of DNA binding sites

Card 3

Front

How do enhancer sequences regulate transcription?

Back

Preview of the front of card 3

Card 4

Front

What does the transcription factor do?

Back

Preview of the front of card 4

Card 5

Front

What forms the nucleosome?

Back

Preview of the front of card 5
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