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Enzymes AP Biology 2007-2008 Exothermic vs. endothermic reactions exothermic endothermic - energy released - digestion - energy invested - synthesis +G -G All chemical reactions require energy AP Biology G = change in free energy = ability to do work Activation energy Breaking down large molecules requires an initial input of energy activation energy large biomolecules are stable must absorb energy to break bonds AP Biology cellulose energy CO2 + H2O + heat Too much activation energy for life Activation energy moves the reaction over an “energy hill” glucose AP Biology Why is activation energy important?? Reducing Activation energy Catalysts reducing the amount of energy to start a reaction uncatalyzed reaction Pheeew… that takes a lot less energy! catalyzed reaction NEW activation energy reactant product AP Biology Catalysts So what’s a cell got to do to reduce activation energy? get help! … chemical help… ENZYMES Call in the ENZYMES! G The ENZYMES are here AP Biology Enzymes Biological catalysts Proteins facilitate chemical reactions increase rate of reaction without being consumed reduce activation energy don’t change free energy (G) released or required required for most biological reactions highly specific thousands of different enzymes in cells AP Biology control reactions of life Enzymes vocabulary substrate reactant which binds to enzyme enzyme-substrate complex: temporary association product end result of reaction active site enzyme’s catalytic site; substrate fits into active site active site substrate enzyme AP Biology products Lock and Key model Simplistic model of enzyme action substrate fits into 3-D structure of enzyme’ active site H bonds between substrate & enzyme AP Biology like “key fits into lock” In biology… Size doesn’t matter… Shape matters! Induced fit model More accurate model of enzyme action 3-D structure of enzyme fits substrate substrate binding cause enzyme to change shape leading to a tighter fit “conformational change” bring chemical groups in position to catalyze reaction AP Biology Properties of enzymes Reaction specific each enzyme works with a specific substrate H bonds & ionic bonds between active site and substrate Not consumed in reaction single enzyme molecule can catalyze thousands or more reactions per second Affected by cellular conditions any condition that affects protein structure temperature, pH, salinity - Denaturation AP Biology Naming conventions Enzymes named for reaction they catalyze sucrase breaks down sucrose proteases break down proteins lipases break down lipids DNA polymerase builds DNA adds nucleotides to DNA strand pepsin breaks down proteins (polypeptides) AP Biology Got any Questions?! AP Biology 2007-2008 Factors that Affect Enzymes AP Biology 2007-2008 Enzyme concentration reaction rate as enzyme = reaction rate enzyme concentration AP Biology What’s happening here?! Substrate concentration reaction rate as substrate = reaction rate substrate concentration AP Biology What’s happening here?! Temperature Optimum T° greatest number of molecular collisions reaction rate What’s happening here?! 37° temperature AP Biology Optimal To Enzymes and temperature Different enzymes function in different organisms in different environments reaction rate human enzyme hot spring bacteria enzyme 37°C AP Biology temperature 70°C (158°F) pH What’s happening here?! trypsin reaction rate pepsin pepsin trypsin 0 AP Biology 1 2 3 4 5 6 pH 7 8 9 10 11 12 13 14 Salinity reaction rate Salinity is salt concentration salt concentration AP Biology What’s happening here?! IMPORTANT!!!!! So sit up! Compounds which help enzymes cofactors coenzymes non-protein small inorganic non-protein organic compounds & ions molecules bound within enzyme molecule Examples: Mg, K, Ca, Zn, Fe, Cu bind temporarily or permanently to enzyme near active site Examples: many vitamins NAD (niacin; B3) FAD (riboflavin; B2) Coenzyme A AP Biology Show me some coenzymes homeskillet! Fe in hemoglobin Mg in chlorophyll AP Biology Compounds which regulate enzymes Inhibitors molecules that reduce enzyme activity competitive inhibition noncompetitive inhibition feedback inhibition AP Biology Competitive Inhibitor Inhibitor & substrate “compete” for active site disulfiram (Antabuse) treats chronic alcoholism blocks enzyme that breaks down alcohol severe hangover & vomiting 5-10 minutes after drinking How can I beat a competitive inhibitor? AP Biology Non-Competitive Inhibitor Inhibitor binds to site other than active site allosteric inhibitor binds to allosteric site causes enzyme to change shape conformational change active site is no longer functional binding site keeps enzyme inactive AP Biology Metabolic pathways ABCDEFG 5 6 enzyme enzyme enzyme enzyme enzyme enzyme enzyme 1 2 3 4 Many enzymes are used in chemical reactions efficiency control = regulation When might Inhibitors be helpful? AP Biology Feedback Inhibition Regulation & coordination of production product is used by next step in pathway final product is inhibitor of earlier step allosteric inhibitor of earlier enzyme feedback inhibition no unnecessary accumulation of product ABCDEFG 1 2 3 4 5 6 X enzyme enzyme enzyme enzyme enzyme enzyme AP Biology allosteric inhibitor of enzyme 1 threonine Feedback inhibition Example synthesis of amino acid, isoleucine from amino acid, threonine isoleucine becomes the allosteric inhibitor of the first step in the pathway as product accumulates it collides with enzyme more often than substrate does AP Biology isoleucin e Don’t be inhibited! Ask Questions! AP Biology 2007-2008 Extra Info AP Biology Factors affecting enzyme function pH changes in pH adds or remove H+ disrupts bonds, disrupts 3D shape disrupts attractions between charged amino acids affect 2° & 3° structure denatures protein optimal pH? most human enzymes = pH 6-8 depends on localized conditions pepsin (stomach) = pH 2-3 trypsin (small intestines) = pH 8 AP Biology 0 1 2 3 4 5 6 7 8 9 10 11 Factors affecting enzyme function Salt concentration changes in salinity adds or removes cations (+) & anions (–) disrupts bonds, disrupts 3D shape disrupts attractions between charged amino acids affect 2° & 3° structure denatures protein enzymes intolerant of extreme salinity Dead Sea is called dead for a reason! AP Biology