9-25-09_kinetics2A - Enzymes are things invented by...

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Enzymes are things invented by biologists that explain things which otherwise require harder thinking” –Jerome Lettvin Pinky : Egad. You astound me, Brain. Brain : That's a simple task, Pinky.
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Quiz 3 available today at noon. Due Wednesday at noon. Covers through today’s class. Research article summary due October 5, 2009. “How to read a research article” posted on Blackboard in “Papers for Written Assignments” folder.
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What a catalyst does A catalyst lowers the activation energy (E A ) of a reaction – increasing the fraction of molecules that can reach the transition state - reaction proceeds faster in both directions - No effect on position of equilibrium – because G initial and final do not change, Keq = k +1 /k -1 www.bioweb. uncc .edu/Faculty/Yengo/images/ Enzyme %20 Catalysis %203. ppt -
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Schematic of enzyme action (adapted from Briggs and Haldane 1925) Substrate binding - Substrate wanders at random until finds enzyme. Enzyme shape – similar but not identical to substrate Deformation of E and S to lower free energy and complement binding interactions – ES formation Altering E and S conformations is called the “induced fit” model Reduce activation barrier of bond of interest by deformation from ES interactions ES isomerizes to EP – increased rate of S to P than without enzyme Product dissociation www.bioweb. uncc .edu/Faculty/Yengo/images/ Enzyme %20 Catalysis %203. ppt -
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Models of How Enzymes Act Catalysts Active Site – location where the reactants (substrate) bind with specificity – pocket or cleft - lock and key hypothesis Active site
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Transfer of phosphate from PEP to ADP is catalyzed by PEP kinase through substrate alignment The active site confers substrate specificity
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Non-covalent bonds usually bind substrate to enzyme Sites of interaction between ribulose bisphosphate (RuBP), CO2, and the enzyme RuBP decarboxylase (Rubisco) Enzyme substrate interactions bring molecules very close to one another (often 2-5 angstroms), so the weaker bonds are important
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Change in charge environment is another enzymatic mechanism Can very locally change reactivity of amino acid side chains
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After binding a substrate, complex may undergo conformational changes that promote transitions through intermediate states
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Example: Glucose binding to hexokinase induces a shape change When glucose binds, hexokinase shifts to put mechanical strain on bonds
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This note was uploaded on 02/09/2010 for the course BIOL 230 taught by Professor Bartlett,e during the Fall '08 term at Purdue University-West Lafayette.

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9-25-09_kinetics2A - Enzymes are things invented by...

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