lecture03 - Biology 172 Lecture 3 Monday Todays Outline...

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1 Lecture 3: Monday, May 10, 2010 Biology 172 Today’s Outline Announcements • Tomorrow’s Discussion: Enzymes. No Quiz (meet at Science learning ctr.) ENZYMES : Activation Energy Enzymes Specificity • Kinetics • Molecular Structure • Regulation Enzymes and Drugs
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2
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3 Example of exergonic reaction – Figure 3.18 Activation energy (E A ) – energy required for reactants to reach the transition state (unstable intermediate) …..can be overcome by heat or a catalyst Transition state Reactants Products Activation energy
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4 Effect of a Enzyme on a reaction - Fig 3.19 - does increase the rate of the reaction - is not itself changed by the reaction - does lower the energy of activation, E A
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5 enzymes are substrate- specific Characteristics of Enzyme Action region that binds substrate is active site binding involves interactions between enzyme’s R-groups and substrate binding destabilizes bond(s) in substrate Substrates Products Enzyme Enzyme-substrate complex
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6 Specificity: induced fit between enzyme and its substrate Fig. 3.20
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7 What do enzymes do ? Active site binds substrates (reactants) –> substrate specificity Binding involves interactions between enzyme’s R-groups and substrate Binding destabilizes chemical bonds in substrate –> lowers the activation energy –> reaction goes faster Substrates (S) Active site* Products (P) Enzyme (E) ES complex Figure 3-22
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8 Enzyme Kinetics Basic enzymatic reaction: Reaction Rate = amount of product formed (or substrate used) time S + E ES E + P
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9 Enzyme Kinetics V = rate of reaction [S] = substrate conc. V max is reached when enzyme is processing substrate to product as fast as it can (saturation)
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10 Reaction rate (V) Substrate Concentration [S] V max is reached when enzyme is processing substrate to product as fast as it can (saturation) K M is the substrate concentration when the reaction rate is half maximum Enzyme Kinetics 1/2 V max
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12 V = rate of reaction [S] = substrate conc. 2 enzymes 4 enzymes Enzyme Concentration Affects Vmax, but not Km
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13 Enzyme K M Depends on Affinity for Substrate M
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14 K M describes the affinity of an enzyme for its substrate. A low K M means that the enzyme holds the substrate tightly ( high affinity ) and is very efficient at converting it to product. A high K M means that the enzyme holds the substrate more loosely ( lower affinity ) and is less efficient at converting it to product.
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15 Do Enzymes Act Alone?
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