Chapter 6 (Fall2010)

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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

BIOA01FALL2010 CHAPTER 6 Energy Enzymes and Metabolism 63 What are EnzymesRate of reaction the speed at which the reaction moves towards equilibriumCatalysts substances that speed up a reaction without being permanently altered by that reactionEnzymes made of protein biological catalystsActivation energy the energy barrier represents the amount of energy needed to start the reactionIn a chemicalthe activation energy is the energy needed to change the reactants into unstable molecules called transitionstate speciesThey have higher free energies than either the reactants or the productsCan use kinetic energy of motion to overcome barrierSubstrates reactants in a catalyzed reactionSubstrates bind to a special site called the active site and catalysis occursSpecific 3D shape where only substrates can fitEnzymesubstrate complex held together by hydrogen bonding electrical attraction or covalent bondingLowers activation energy for the reaction but not change the equilibrium stateTherefore reaction speeds up 64 How do Enzymes workEnzyme orient substratesEnzyme induce strain in the substrateunstable transition stateEnzymes temporarily add chemical groups to substratesside chains of amino acids of enzyme can make substrate more reactiveacidicbase catalysismay transfer H to or from the substrate destabilizing a covalent bond in the substrate and so permitting it to breakcovalent catalysis functional group oin side chain forms a temporary covalent bond with a portion of the substratemetal ion catalysismetal ions such as copper and iron can firmly bound to side chains of the enzyme can lose or gain electrons without detaching from the enzyme therefore making them important in redox reactionsActive site is specific to the substrateEnzyme changes shape when it binds to the substrate induced fit causes side chains to become ligned with the substrate and therefore facilitating catalysisSome enzymes require other molecules cofactors iron copper zincredox reaction bind to enzymescoenzymes biotin coenzyme A NAD FAD ATPcarbon containing mo
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