Presentation on theme: "Enzymes Biological catalysts Increase rate of reactions"— Presentation transcript:
1 Enzymes Biological catalysts Increase rate of reactions by lowering activation energy (EA)Spontaneous reactions can take a long time!Need enzymes to speed reactions for cell survival
2 Activation Energy (EA) Needed to destabilize bonds of reactants
3 Could raise temp. to break bonds A B C D Transition state A B EA LE 8-14ABCDTransition stateCould raise temp.to break bondsABEAFree energyCDReactantsABDG < OCDProductsProgress of the reaction
4 Why don’t cells rely on increases in temperature to break bonds? Because proteins could be denatured causing cell damage.
5 Progress of the reaction LE 8-15Course ofreactionwithoutenzymeEAwithoutenzymeEA withenzymeis lowerReactantsFree energyCourse ofreactionwith enzymeDG is unaffectedby enzymeProductsProgress of the reaction
6 LE 8-13Example:SucroseC12H22O11GlucoseC6H12O6FructoseC6H12O6
7 Structure & Function of Enzyme DRAW Enzymes bind substrate molecules (the reactant)Substrates bind to active site on enzymeBinding induces conformational change in enzyme--better ”fit” for substrateActive sites are highly specific and discriminatory i.e. sucrase does not accept lactose
8 LE 8-16SubstrateActive siteEnzymeEnzyme-substratecomplex
9 How does enzyme lower activation energy of reaction? Orients substrates for optimal interactionStrains substrate bondsProvides a favorable microenvironment-May covalently bond to the substrate
10 LE 8-17Substrates enter active site; enzymechanges shape so its active siteembraces the substrates (induced fit).Substrates held inactive site by weakinteractions, such ashydrogen bonds andionic bonds.Active site (and R groups ofits amino acids) can lower EAand speed up a reaction byacting as a template forsubstrate orientation,stressing the substratesand stabilizing thetransition state,providing a favorablemicroenvironment,participating directly in thecatalytic reaction.SubstratesEnzyme-substratecomplexActivesite isavailablefor two newsubstratemolecules.EnzymeProducts arereleased.Substrates areconverted intoproducts.Products
11 Environmental Conditions Affect Enzyme Function ?Temperature: cold-->decreased chance of bumping into substratehot--> good chance of substrate interaction butchance of denaturation at some pointpH->change in charge (H+ or OH-) can denature proteinsand substrateExamples of pH sensitive enzymes?
12 What is your normal body temp.? LE 8-18 Optimal temperature for typical human enzymeOptimal temperature forenzyme of thermophilic(heat-tolerantbacteria)What isyournormalbodytemp.?Rate of reaction20406080100Temperature (°C)Optimal temperature for two enzymesOptimal pH for pepsin(stomach enzyme)Optimal pHfor trypsin(intestinalenzyme)Rate of reaction12345678910pHOptimal pH for two enzymes
13 Cofactors Non-protein enzyme helpers (like metal, Fe) Coenzymes organic cofactors (con-enzyme A)Vitaminse.g. Vitamin K: required for blood clotting &Required in certain carboxylation reactions
14 Regulation of Enzymes Enzyme Inhibitors Competitive inhibitorbinds to active site of enzymeblocks substrate binding by competitionNoncompetitive inhibitorbinds to another part of enzymecauses enzyme to change shapeprevents active site from binding substrateAllosteric effectDRAW
15 Example of allosteric effect A substrate canbind normally to theactive site of anenzyme.SubstrateActive siteEnzymeNormal bindingA competitiveinhibitor mimics thesubstrate, competingfor the active site.CompetitiveinhibitorCompetitive inhibitionA noncompetitiveinhibitor binds to theenzyme away from theactive site, altering theconformation of theenzyme so that itsactive site no longerfunctions.Example of allosteric effectNoncompetitive inhibitorNoncompetitive inhibition
16 Allosteric Regulation of Enzymes Where protein function at one site is affected by binding of a regulatory molecule at another siteMay inhibit or stimulate enzyme activity
17 Allosteric Activation and Inhibition Most allosterically regulated enzymes are made from polypeptide subunitsactive and inactive formsbinding of activator stabilizes active form of enzymebinding of inhibitor stabilizes inactive form of enzyme
18 Active site (one of four) LE 8-20aAllosteric activatorstabilizes active form.Allosteric enzymewith four subunitsActive site(one of four)Regulatorysite (oneof four)ActivatorActive formStabilized active formOscillationAllosteric inhibitorstabilizes inactive form.Non-functionalactive siteInhibitorInactive formStabilized inactiveformAllosteric activators and inhibitors
19 Binding of one substrate molecule to LE 8-20bBinding of one substrate molecule toactive site of one subunit locks allsubunits in active conformation.SubstrateInactive formStabilized active formCooperativity another type of allosteric activation
20 Shift from regulation of one enzyme to regulation of an enzymatic pathway
21 Feedback InhibitionEnd product of a metabolic pathway shuts down the pathwayPrevents over-production of unneeded molecules
22 LE 8-21 Initial substrate (threonine) Active site available Threonine in active siteEnzyme 1(threoninedeaminase)Isoleucineused up bycellIntermediate AFeedbackinhibitionEnzyme 2Active site ofenzyme 1 can’tbindtheoninepathway offIntermediate BEnzyme 3Intermediate CIsoleucinebinds toallostericsiteEnzyme 4Intermediate DEnzyme 5End product(isoleucine)
23 Metabolic pathways are often localized in cell Cellular structures organize and concentrate components of enzymatic pathwayse.g. organelles (mitochondria, chloroplast, lysosomes)Pathways: respiration, photosynthesis, hydrolysis
24 sites of cellular respiration LE 8-22Mitochondria,sites of cellular respiration1 µm
25 It’s nice to get so much attention! LE 8-22It’s nice to get so much attention!
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