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35 Cards in this Set
- Front
- Back
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What is the stationary phase?
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growth is arrested when the bacterial cells have reached a certain density of population
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At what density do most stationary phases occur?
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10^9 cells
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What else can cause stationary phase?
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nutrient limitation, oxygen limitation, or waste toxicity
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What controls stationary phase?
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sigma factor S
Sigma 38 which is the product of the rpoS gene |
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How much of the genome does sigmaS regulate?
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about 10%
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What two things do cells do in response to starvation which activate the SigmaS regulon?
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-in the short term: switch nutrition source
- long term : induce stationary phase |
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What two processes are most of the cellular resources allocated to?
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Growth/Reproduction and Maintenance/survival
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Where are resources allocated in Feast and in Famine?
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Feast: mostly reproduction, some maintenance
Famine: most maintenance, some reproduction |
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what happens during stationary phase? How do cell numbers change?
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They stay the same, probably due to some cells replicating while others are dying at the same rate
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What happens to B-Gal when cells start to starve?
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when cells start to starve, there is an accumulation of sigma S. Beta-Gal is then produced and levels of SigmaS start to lower.
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Where are the 3 promotors for rpoS?
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nlpD gene and rpoS gene form a txn operon with three main promotor regions in the nlpD portion, this will translate functional rpoS gene
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What is the major promotor for the rpoS gene?
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the rpoS promotor
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How is rpoS mRNA translationally inhibited?
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the mRNA folds into secondary structure, that contains the shine-delgarno sequence inhibiting translation
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What does DsrA do?
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it is an anti-antisense RNA which allows high levels of rpoS translation by relieving the secondary structure allowing the ribosome to bind
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When is DsrA unregulated?
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when temperatures are low, so that more sigmaS can be made
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What does the mRNA do that is energetically unfavourable for the cell?
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The rpoS mRNA is always being made, and degraded quickly so it is energetically unfavourable, however when this mRNA is actually needed it does lower the energetic load.
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What other molecule behaves like DsrA stimulating translation?
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RprA
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What type of RNA are RprA and DsrA?
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small RNA's - they are regulatory RNA's so they influence regulation of other genes at low temps that can trigger stationary phase
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What is ArcZ?
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-Similar to RprA and DsrA because they positively regulate translation of Sigma S
-also an sRNA regulator of rpoS |
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What does ArcZ respond to?
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Low Energy, High oxygen conditions
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How does DsrA control translation?
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-hfq is needed for translational initiation of sRNA's
-hfq binds in middle of RNase E cleavage site preventing cleavage of the mRNA |
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Why does oxyS inhibit rpoS translation?
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it inhibits stationary phase in response to low oxygen because you don't want to induce whole response. OxyS sequesters the hfq from DsrA allowing for cleavage of DsrA and no translation of the rpos mRNA
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How is DsrA a positive regulator of stationary phase?
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-It inhibits other pathways while inducing positive regulation of the rpoS mRNA
-acts like an activator and a repressor at the same time |
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Why are there multiple RNA's to regulate rpoS?
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so you can get the same type of stationary response to different signals/conditions.
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What is a three component system?
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System that has one histidine kinase ( ArcB) and 2 response regulators ( ArcA and RssB) which can down regulate or up regulate sigmaS in response to different conditions
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What does ArcB do?
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It is the histidine Kinase which will phosphorylate the Response Regulator either ArcA or RssB
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What happens when ArcA is phosphorylated?
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It will inhibit rpos transcription
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What happens when RssB is phosphorylated?
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It destabilizes SigmaS
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what happens in conditions of high energy and Low oxygen?
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-ArcA and RssB are both phosphorylated.High energy in the cell causes RssB to be made and it will induce Sigma S proteolysis which will down regulate Sigma S which stops stationary phase.
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What happens in conditions of low energy and High Oxygen?
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ArcA is phosphorylated which inhibits RssB. Phosphorylated ArcA will still inhibit rpoS transcription but other signals made during this condition will induce it causing txn of rpoS and up regulation of sigmaS
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How is Sigma S degraded in the high energy, low oxygen condition?
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-SigmaS interacts with RssB-P, RssB-P then delivers sigmaS to clpXP (protease chaperone)
-sigmaS is degraded in presence of phosphorylated clpXP |
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What is ArcZ?
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-protein expressed in high oxygen low energy conditions
-it inhibits production of ArcB which increases translation of rpoS |
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What happens to Arcz under low oxygen high energy conditions?
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ArcB phosphorylates ArcA inhibiting transcription of arcZ, which limits translation of rpoS
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What is ClpXP?
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protease system of E.Coii, degrades rpoS when phosphorylated.
- rpoS will be stabilized when Ira proteins prevent RssB from binding rpoS and delivering them to clpXP |
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Why do CAP/CRP and LRP proteins affect sigmaS?
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Because those proteins are an indication of low glucose so you are interacting with the stationary phase
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