Enzymes - Enzymes 1 Last Time Measuring the energy that can...

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Unformatted text preview: Enzymes 1 Last Time Measuring the energy that can perform work in the cell - Free energy - G Free energy and metabolism - exergonic and endergonic reactions Coupling exergonic reactions with endergonic reactions to do work 2 Enzymes Enzymes are proteins speed up exergonic chemical reactions Enzyme activity is affected by the cellular environment pH and temperature Regulation of enzyme activity Allosteric inhibition and activation Feedback 3 4 Sucrase = enzyme Exergonic ....however, will not happen quickly. Enzymes speed up exergonic reactions Fig. 8.13 http://www.lifeplusvitamins.com/images/captain-enzyme-3.jpg 5 Activation energy Activation energy (EA) - pushes reaction over energy barrier, so "downhill" part of reaction can occur Fig. 8.14 6 Enzymes lower activation energy barrier 7 Enzymes force reactants into unstable forms Reactants - move towards lower energy state (high free energy to low free energy) Allowing reaction to proceed. 8 Important points Exergonic reactions are spontaneous, -!G Rate can be slow because of the energy barrier - reactants require a small amount of energy to clear the energy barrier Enzymes DO NOT affect the !G of the reaction - Enzymes lower the activation energy (EA) required for the reaction to occur quickly. Enzymes affect RATE of reaction 9 How do enzymes work? (reactant) 10 ("induced fit" between enzyme and substrate) the handshake 11 1000 molecules per second! 12 Enzyme mechanisms for lowering EA 1. allows substrates to assemble in proper orientation 2. enzyme can stretch the bonds towards `transition state' conformation 3. provides appropriate microenvironment for reaction to occur 4. brief covalent interaction between side chain of amino acid and substrate 13 Enzymes are proteins! Denaturation properly folded protein denatured protein Renaturation 14 Temperature Environmental factors affect enzyme activity pH 15 Enzyme `helpers' Co - factors inorganic metals, like Cu, Mg, Zn, Fe Co - enzymes organic molecules, like Vitamins 16 Summary Enzymes are proteins that lower the EA of exergonic chemical reactions Enzymes, like all proteins, can be denatured depending on the environment Enzymes have optimal pH and temperatures for maximum function Sometimes associate with co-factors, which assist in the catalysis 17 Regulation of enzyme activity Inhibition competitive inhibition noncompetitive inhibition Activation Feedback 18 Competitive inhibitors Normal binding Competitive binding 19 Noncompetitive inhibitors Normal binding Non competitive inhibitor binding 20 Inhibitors Competitive - mimics - resemble normal substrate - bind active site - often reversible Noncompetitive - bind another part of enzyme (not active site) - enzyme changes shape as a result - loses activity 21 Regulation of metabolism allosteric regulation can inhibit enzyme activity can activate enzyme activity Allo = "shape" Steric = "space" protein's function at one site is affected by a protein binding at another site 22 Allosteric activator Fig. 8.20 23 Allosteric inhibitor 24 Cooperativity 25 Summary Enzymes are proteins speed up exergonic chemical reactions Enzyme activity is affected by the cellular environment pH and temperature Regulation of enzyme activity Allosteric inhibition and activation 26 Next Time Respiration: electron transfer http://www.cbs.dtu.dk/staff/dave/roanoke/mitochondriadrawing.gif 27 ...
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