CH08b_6_ - Enzymes Overview Overview Enzymes Overview...

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Unformatted text preview: Enzymes Overview Overview Enzymes Overview Overview Most enzymes are proteins Catalytic Cycle Factors influencing rate of enzyme-catalyzed reaction enz me Enzyme inhibitors Some are RNA (ribozymes) Role: catalyze reactions l substrates, products lower EA Competitive Non-Competitive Non- Specificity Definition of Enzymes Enzymes are proteins (& RNA) that catalyze chemical reactions in living organisms reactions Fig. 8-13: Sucrose Hydrolysis by Sucrase 8- Sucrose Glucose + Fructose Fig. 8-17: 8Enzyme’s Catalytic Cycle InducedInduced-Fit Hypothesis Fig. 8-16 8- Bio 230, Summer 2010, Ch8b, Page 1 Definition of Enzymes Fig. 8-14: Exergonic Reactions 8- As catalysts enzymes: Speed rate of reaction Are not consumed by reaction Can’t change G G (-) Can’t change a non-spontaneous nonreaction into a spontaneous reaction Can change activation energy: (EA) Fig. 8-14: Endergonic Reactions 8- Exergonic Reaction w & w/o Enzyme Figs. 8-15 8Transition G (+) Free Energy (G) Reaction without enzyme EA Reaction with enzyme Substrates Reaction Progress 20% 25o C 60% 30% 150o C 10% G G (-) Products G 20% 30% Enzyme Enzyme 5% Free Energy (G) Number of Molecules 75% Enzyme Enzyme Exergonic Reaction w & w/o Enzyme Thermal Energy Levels of Substrates 4o C EA With EA Without 50% Reaction Progress Bio 230, Summer 2010, Ch8b, Page 2 Exergonic Reaction w & w/o Enzyme 4oC Exergonic Reaction w & w/o Enzyme 25o C 5% Reaction runs w/o enzyme 10% Reaction runs w/o enzyme 20% Reaction runs with enzyme 30% Reaction runs with enzyme 60% Reaction does not run N G Reaction Progress 150o C Reaction does not run N G Reaction Progress Exergonic Reaction w & w/o Enzyme 20% Reaction runs with enzyme Enzyme Mechanisms Reaction runs w/o enzyme 50% 30% Free Energy (G) Free Energy (G) Free Energy (G) 75% How enzymes can lower EA: Reaction does not run N G Change acid/base environment of substrate Attack substrates with reactive R groups on amino acids surrounding active site Example: Serine Proteases Reaction Progress Enzyme Mechanisms How enzymes can lower EA Bend substrate so that bonds are strained Stabilize transition state Factors Influencing Rate of Reaction Substrate and product concentrations Reaction is saturable is saturable Bio 230, Summer 2010, Ch8b, Page 3 ConcentrationConcentration-Dependence ConcentrationConcentration-Dependence MichaelisMichaelis-Menten Equation: Vmax Vmax [S] V= Vm/2 Km + [S] V= Vmax [S] Km + [S] Km Temp and [E] are constant Factors Influencing Rate of Reaction ConcentrationConcentration-Dependence Amount of enzyme Vmax 50% [Enzyme] Temp is constant Factors Influencing Rate of Reaction TemperatureTemperature-Dependence Fig. 8-18a 8- Temperature denaturation at excess temperature temperature Denaturation Denaturation [E] is constant Bio 230, Summer 2010, Ch8b, Page 4 Fig. 5-20: Temp & Protein Tertiary Structure Val Ser Factors Influencing Rate of Reaction pH Changes charge on titratable groups such as NH groups such as NH2 and COOH COOH Val Cys Cys Asp Lys Asp Factors Influencing Rate of Reaction pHpH-Dependence Fig. 8-18b 8- Substrate and product concentrations Enzyme concentration concentration Temperature pH Stomach Small Intestine Temp and [E] are constant Fig. 5-20: pH & Protein Tertiary Structure Val Ser Salt concentrations Cofactors Val Cys Inorganic constituents Cys E.g., Mg++ Asp Lys Factors Influencing Rate of Reaction Asp Coenzymes (organic) E.g., NAD+ Inhibitors Bio 230, Summer 2010, Ch8b, Page 5 Inhibition of Enzymes Fig. 8-19a 8- Competitive Inhibitor Fig. 8-19b 8- Inhibition of Enzymes Competitive: Inhibitor competes with substrate for active site on enzyme active site on enzyme ConcentrationConcentration-Dependence Vmax Competitive Inhibitor Resembles substrate Acts as if substrate concentration has been lowered NonNon-Competitive Inhibitior Fig. 8-19c 8- 50 Inhibition of Enzymes Non-Competitive: Inhibitor Noninactivates enzyme at site other than active site than active site Does not necessarily resemble substrate Acts as if enzyme concentration has has been lowered Bio 230, Summer 2010, Ch8b, Page 6 ConcentrationConcentration-Dependence Inhibition of Enzymes Significant enzyme inhibitors: Vmax Non-Comp Inhibitor Inhibitor Allosteric Regulation penicillin nerve gas heavy metals anti-HIV protease inhibitors anti- Allosteric Regulation Fig. 8-20a2 8- Fig. 8-20a1 8- Cooperativity ConcentrationConcentration-Dependence Vmax Normal Fig. 8-20b 8- Cooperative Temp and [E] are constant Bio 230, Summer 2010, Ch8b, Page 7 Feedback Inhibition (Ile Synthesis) Fig. 8-21 8- Bio 230, Summer 2010, Ch8b, Page 8 ...
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This note was uploaded on 11/28/2011 for the course BIOL 230 taught by Professor J.breckler during the Spring '11 term at S.F. State.

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