Chapter 13

Chapter 13 - Chapter 13 enzymes o proteins and RNA...

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Chapter 13 enzymes o proteins and RNA specialized to catalyze metabolic reactions o can catalyze thermodynamically favorable reactions by lowering E a o provide cells w/ ability to exert kinetic control over thermodynamic potentiality o form metabolic pathways (nutrients degraded, energy released and converted into useful forms) o regulatory enzymes: set at key junctions; capable of sensing momentary metabolic needs of cell and adjusting catalytic rates accordingly Enzyme Characteristics o catalytic power enzyme-catalyzed rate of reaction : uncatalyzed rate of reaction; can be as much as 10 16 o specificity: very selective in substrates and the rxns it catalyzes; no wasteful by-prod.; active sites are specific; controlled by structure o regulation of enzymes in many ways o nomenclature: traditionally w/ -ase oxidoreductase: oxid-red. rxns transferases: transfer of functional groups hydrolases: hydrolysis rxns lysases: addition to double bonds isomerases (isomerization rxns) ligases: formation of bonds w/ ATP cleavage o coenzymes and cofactors provide proteins w/ chemically versatile functions not found in aa side chains tend to be heat stable conenzymes (type of cofactor), usuallyfirmly associated w/ enzyme prosthetic groups: tightly bound coenzymes holoenzyme vs. apoenzyme Rate of Enzyme-Catalyzed Reaction o kinetics: branch of science concerned w/ rates of chemical rxns o enzyme kinetics: addresses biological roles of enzymatic catalysts and how they accomplish their feats o irreversibility assumed for A P if P A is slow/[P] is negligible under the conditions
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o rate/velocity: amount of P formed/A consumed per unit time o rate constant: k (in 1/s); proportionality constant o order: given by exponent in rate equation; almost always 1 st or 2 nd order found o molecularity: number of molecules that must simultaneously interact; >2 rarely found, >3 = never found o rxns almost always proceed via unimolecular/bimolecular elementary steps o transition state: reactive condition; probability very high that particular
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Chapter 13 - Chapter 13 enzymes o proteins and RNA...

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