Lecture 25

Lecture 25 - Lecture 25 Monday 9:56 AM I II A B III...

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Announcements I. Regulation of carbon assimilation II. A ccp system in Gram Positive A. Light-dark transition in cyanobacteria B. Chemotaxis III. Review session on Sunday Gram Pos don’t make cAMP, no phosphorylation cascade. But they do have a catabolite regulator. Catabolite repression in Bacillus subtilis HPr activated by kinase and addition of Pi from ATP. Kinase activated by FBP. Resulting in HPr~P. HPr~P + CcpA + FBP = catabolite repression. Signal: high carbon interpreted as Fructose bisphosphate -- FBP activates the kinase and bind to the regulatory element. Messenger: HPr~P Effector: HPr~P (binds to regulatory element, CcpA, as a dimer) plus CcpA-FBP The level of FBP will determine how much this catabolic repression complex is created. Redox control of CO2 assimilation in cyanobacteria When light is not on, it must still alive, during the dark cycle there is stil processes going. Cyanobacteria focused on Reductive Pentose Phosphate metabolism : depedent on one key enzyme, phospho ribulose kinase. GAP-DH is NADPH dependent -- acid to aldehyde FBP Phosphatase Oxidative Pentose Phosphate cycle Two key enzymes: Glucose 6 phosphate DH 6 Phosphogluconate DH The cell want to work these pathways independently. Cells want to do the REDPP in light Cells want to do the OXPP w/o light to make its precursors. How do cells know if the light is on or off? They know from the e- transport chain, at the end of the chain based on level of reduced Ferredoxin. Ferredoxin is stable, it can reduce many proteins, NADPH, etc. so it is not Fd itself but the protein that Fd reduces. Signal: Fd Messenger Thioredoxin Tdreduced Fd R-S-H H-S-R R-S-S-R Thioredoxin reduces disulfide bonds When light goes off, Fd will drop, no Td. In light Thioredoxin can mess with/reduce all four proteins. Disulfide bridges reduced. Which will be inactive when disulfide is reduced? Enzymes: (D) (A,B,C)--all reduced and active when light is on. Chemotaxis: Coordinated cell movements: cells move by a random walk mechanisms. Lecture 25 Monday, November 28, 2011 9:56 AM MIC140 Page 1
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Bacterial cells can move: Swim 1. Twitch 2. Glide 3. Swimmers must have volume to swim towards Gliding and twitching must have contact with a substrate. Most of these movements are random with no seeming purpose, only when they sense something good they will move with purpose. Taxis: movement toward or away from stimulus. Chemotaxis: ability of a bacteria to move to or away from a chemical concentration gradient. Phototaxis: light Magnetotaxis: magnetic field Aerotaxis: oxygen Run vs. tumble Motility occurs by runs, counter clockwise rotation of the flagellum in e.coli Tumbles change direction---biased random walk. When it picks up a signal, it has a longer run than a tumble.
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Lecture 25 - Lecture 25 Monday 9:56 AM I II A B III...

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