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24 Cards in this Set
- Front
- Back
Why do we need to control gene expression? |
Different cell types, vary massively in size structure and function eg compare neuron to another cell |
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3 experiments that prove theres no loss of DNA during development |
1. Nucleus of fully differentiated frog injected into a frog egg cell whos nucleus has been removed, develops into normal tadpole 2. Chromosomes have same banding pattern in the same cell of every individual |
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At what levels can gene expression be regulated? |
1. DNA processing - DNA can be re-arranged, amplified or activated |
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Where does the majority of gene control take place? |
The transcriptional level |
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What are Cis-regulatory elements? |
regions of non-coding DNA which affects the expression of near-by genes on the same helix |
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What are GRPs? |
Gene regulatory proteins bind to cis dominant recognition element to inflict either positive or negative regulation. they recognise short sections of DNA through structural motifs. |
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What are master regulatory proteins? |
1 GPR which can regulate many genes in different ways eg +ve and -ve regulation. For example, Drosphila has just 30 master regulatory proteins have 300,000 genes to be expressed |
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What's a good example of a master regulatory protein? |
MyoD in muscle cell development. MyoD Myf5 and Myogenin are all master regulators. Stem cells differentiate into myoblasts which differentiate into myotubules all of these processes are controlled by the 3 GPRs which turn many genes on and off during embronic development |
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Describe the tryptophan operon |
5 E.coli genes code for the enzymes that manufacture the amino acid tryptophan. When tryptophan is present in the medium then bacteria no longer needs to express these genes so cuts off their production. |
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Describe the lac operon in response to lactose levels |
lac operon consists of 3 structural genes lac Z= Gene for ß-galactosidase converts lactose into glucose and galactose lac Y=Gene for ß-galactoside permease transports lactose into the cell lac A=Gene for ß-galactoside transacetylase and a promoter, terminator, regulator and an operator. Its under both positive and -ve control In the absence of lactose, lactose repressor binds to the operator so RNA polymerase cannot bind, no gene transcription. |
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Describe the lac operon in response to glucose levels |
CAP (catabolite activator protein) is a GRP for the lac operon and enables E.coli to use alternative food sources in the absence of glucose eg lactose. |
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Describe control of nitrogen metabolism by E.coli |
In time of nitrogen deficiency: 7. ntrC activates transcription |
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What sequences do eukaryotes have that are lacking in prokaryotes? |
Upstream promotor complex = DNA that must be in a fixed position relative to the start of transcription, it can include TATA but excludes promoter |
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What experiments were carried out to find GPR binding domains? |
1. Mutational analysis - took enchancer for beta-globulin which is 108bp long and mutated every 4th base giving 27 mutant forms. Insert into a plasmid with beta-globulin promoter and a reporter gene and test see which mutation blocks binding of GPR, map activity |
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How do GPRs at enchancers and upstream promoter complex act combinationally? |
GAL4 in yeast bound at enchancer and flips over to help load transcription factors at TATA box |
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How many domains do GRPs have? |
2, shown by domain swap experiments. |
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how do GRPs bind? |
recognise a DNA sequwnce because their surfaced are highly complimentary. Makes a series of contacts with the DNA including H bonds, ionic bonds and hydrophobic interactions. |
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What are the 4 types of DNA binding domains? |
Helix-turn-helix |
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Describe helix-turn-helix |
one of simplist and most common motifs found in 100s of DNA binding proteins |
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C2H2 zinc finger |
cystein and histidine co-ordinate a zinc atom creating finger-like projections which project into DNA eg transcription factoer SP1 has a series of 3 zinc fingers |
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Leucine Zipper |
2 alpha helices, one from each monomer. Every 7a.a there is hydrophobic side chain (usually leucine) which is responsible for holding dimers together. beyond dimer interface the 2 helices seperate into Y shape with very basic (postively charged amino acids) which binds to DNA. Eg: AP-1 |
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Helix-loop-helix |
NOT to be confused with helix turn helix this motif is structurally similar to the leucine zipper. Dimerise at helices, can be a heterodimer or a homo dimer, Consists of short alpha helix connected by a loop to a longer alpha helix with basic regions that bind to DNA |
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Intro into DNA re-arrangements |
It is clear that differentiation in higher eukaryotes usually occurs without changes to DNA. In contrast some prokaryotes carry out DNA re-arrangements to activate or inactivate specific genes. This pattern of gene regulation can be stabley inherited to all progeny of the cell lone in contrast to simple, transient changes eg typ operon |
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Describe Phase Variation |
Happens in Salmonella bacteria. |