MICRB 265 (09/27/13) BIOENERGETICS: Part 1 - Energetics and Enzymes (con't) | Part 2 - Fermentation and Respiration

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Microbiology (Biological Sciences)
Brian Lanoil

MICRB 265 (September 27, 2013) BIOENERGETICS: Part 1 – Energetics and Enzymes | Part 2 – Fermentation and Respiration  Enzymes often bind substrates of similar structures Allosteric regulation – binding to enzyme of an effector molecule that causes an increase/decrease in protein activity  Binding of effector molecule to allosteric site  enzyme shape change  substrate’s ability to attach to enzyme is affected  Positive effector – CAUSES binding of substrate to catalyst  Negative effector – PREVENTS binding of substrate to catalyst (by changing the shape of the enzyme  “lock change”) Feedback inhibition of a Sequential Reaction  Concentration of end product acts as modulator. o If concentration is high, it binds to the first enzyme in the pathway (acts as a negative effector) to shut down its own production o Why the first enzyme in a sequential reaction?  Because the intermediates preceding the production of the end product may be toxic Feedback Inhibition: Branched Pathway  Glutamic acid has two production pathways… one for the production of ARGININE and one for the production of PROLINE o They are created on completely disjoint pathways so the feedback inhibition of one does not affect the production of another o Just like in single path sequential reactions, it is the first enzyme in the sequence that gets inhibited when end product concentrations get too high Covalent Modification  Reversible addition of phosphoryl, methyl, or adenyl groups will either inhibit or activate enzyme activity Start of Part II: Fermentation and Respiration Overview of Cell Metabolism “Auto-“ – organism can fix own carbon “Litho-” – organism implements inorganic carbon Mixotrophy – combined chemolithotrophy and chemoorganotrophy  H 2xidizing bacteria will either grow with C2 fixing bacteria or on their own as organotrophs  Some chemolithotrophs lack enzymes for CO fi2ation Respiration and Fermentation  Both are ways of getting ATP o Fermentation via substrate-level phosphorylation o Respiration via oxidative phosphorylation  More energy per molecule created than fermentation  Energized membrane used for phosphorylation  Respiration implements substrate-level phosphorylation too but is it not the cell’s main source of
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