Lecture 3 - 5:9 - Biology 172 Lecture 3: Monday, May 9,...

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1 Lecture 3: Monday, May 9, 2011 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 Example of exergonic reaction – Figure 3.17 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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3 Effect of a Enzyme on a reaction - Fig 3.18 - 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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Proteins RNA Catalysts Enzymes Ribozymes Biological catalysts include enzymes and ribozymes
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Carboxylesterase (Homo sapiens) -ase -ase -ase -ase -ase ENZYMES
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Enzymes are protein catalysts and typically catalyze a single reaction . Most biological chemical reactions occur at meaningful rates only in the presence of an enzyme . Enzymes bring substrates together in specific positions that facilitate reactions and are very specific as to which reactions they catalyze . Cleft or groove on the enzyme where the substrate binds is called the active site.
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7 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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Induced Fit You can think of enzyme catalysis as a lock and key model with the enzyme’s active site representing the lock and the substrate representing the key . HOWEVER , enzyme structure is not static, it is dynamic. when substrate is bound to the active site, the active site often changes conformation and we call this “induced fit”. Induced fit allows tighter binding between enzyme and substrate.
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Specificity: induced fit between enzyme and its substrate strate cose) yme xokinase) When the substrate binds to the enzyme’s active site, the enzyme changes shape slightly. This “induced fit” results in tighter binding of the substrate to the active site Figure 3.19
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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 Enzyme 1. Initiation: Reactants bind to the active site in a specific orientation, forming an enzyme-substrate complex Transition state 3. Termination: Products have lower affinity for active site and are released. Enzyme is unchanged after the reaction. Shape
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Lecture 3 - 5:9 - Biology 172 Lecture 3: Monday, May 9,...

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