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U-M BIOLCHEM 415 - Enzymes: Basic Concepts and Catalysts
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BIOLCHEM 415 Lecture 6 Outline of Last Lecture II. Proteins can be purified according to their different physical properties III. Gel electrophoresis can be used to analyze proteinsIV. Antibodies can be used in protein identification and purificationOutline of Current Lecture I. Introduction to Enzymes and CofactorsII. Review Thermodynamics with respect to enzymesIII. Active sites and their structuresIV. Different types of enzyme catalysisCurrent LectureEnzymes are extremely efficient- greatly increase the rate of reactionsThere are 6 different classes- Oxidoreductases- transferases- hydrolases- lyases- isomerases- ligasesEnzyme cofactors- biological molecules that provide diversity necessary to catalyze a full range of reactions- can occasionally be metals- vitamins are precursersThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- can’t be synthesized in the body- contain enzymes and cofactors necessary to process the vitaminFree energy can tell whether or not a reaction can occur, not how fast- reaction occurs when ΔG < 0- when ΔG > 0 energy must be supplied for the reaction to occur- ΔG dependent on the reactants and productsGibbs Free Energy and EquilibriumA+B <-> C+DΔG° = ΔH – TΔS- ΔG° = Standard free energyΔG = ΔG° + RTln([C][D]/[A][B])- R = gas constant = 1.99 * 10^-3 kcal/K*molAt equilibriumΔG° = - RTln([C][D]/[A][B])ΔG°’ = - RTln([C][D]/[A][B])ΔG°’ = Biological standard at pH = 7Keq’ = [C][D]/[A][B]Increasing the concentration of reactants to a reaction and change a reaction from unfavorable to favorable- decreases ΔG by taking it away from equilibriumEnzymes accelerate rate of reaction- the equilibrium remains the same- activation energy is lowered so the rate can increase- they stabilize transition statesActive Sites of Enzymes- usually clefts in the enzyme’s structure- only a small part of the enzyme- substrates bond here with multiple weak interactions- often composed of noncontiguous amino acids- scattered throughout cleftLock and Key Active site- complementary fit between enzyme and substrateInduced Fit active site- more common- substrate induces conformational change in enzymeCatalytic strategies- Covalent catalyst- active site has reactive group- covalent intermediate is formed- General Acid-Base- active site molecule becomes a proton donor/acceptor- Metal ion- electrophilic catalyst (stabilizes negative charge)- increase acidity of neighboring molecules- alter redox state for an oxidation/reduction reaction- Approximation and Orientation- two or more substrates- bring in optimal proximity and orientation for the reaction to occurSerine Protease Chymotrypsin- Protease- hydrolyzes peptide bonds in proteins- activate H2O- polarizes peptide carbonyl group- stabilizes intermediate- cleave peptide bonds following Trp, Tyr, Phe, and Met- mostly hydrophobic amino acids- uses covalent catalyst to hydrolyze peptide bonds- acyl enzyme intermediate- the active site contains catalytic triad- Ser 195 (nucleophile- His 57 (Acid-Base)- Asp 102 (stabilize protonated states with hydrogen bonds)- oxyanion hole- negative charge on O- h-bond forms - offsets negative chargeSubstrate Specificity of Serine Proteases- Chymotrypsin- cleaves peptide bond on carboxyl side of Met, Phe, Trp, Tyr- Trypsin- cleaves peptide bond on carboxyl side of Lys and Arg- Thrombin- cleaves peptide bond between Arg and Gly in certain sequences- Elastase- cleaves peptide bond on carboxyl side of Ala and


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U-M BIOLCHEM 415 - Enzymes: Basic Concepts and Catalysts

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