11 Figure 8.2 Transformations between kinetic and potential energy On the platform, a diverhas more potential energy.Diving converts potentialenergy to kinetic energy.Climbing up converts kineticenergy of muscle movementto potential energy.In the water, a diver hasless potential energy.
12 The two laws of thermodynamics Figure 8.3The two laws of thermodynamicsHeatChemical energyFigure 8.3 The two laws of thermodynamics.(a) First law of thermodynamics(b) Second law of thermodynamics12
16 Figure 8.6 Free energy changes (G) in exergonic and endergonic reactions (a) Exergonic reaction: energy releasedReactantsProductsEnergyProgress of the reactionAmount ofenergyreleased (∆G<0)Free energyreleased (∆G>0)(b) Endergonic reaction: energy required
18 Figure 8.8 The structure of adenosine triphosphate (ATP) CH–OOCH2HOHNCHCNH2AdenineRiboseO–PPhosphate groups
19 Figure 8.9 The hydrolysis of ATP Adenosine triphosphate (ATP)H2O+EnergyInorganic phosphateAdenosine diphosphate (ADP)P i
20 Figure 8.11 How ATP drives cellular work Motor proteinP iProtein moved(a) Mechanical work: ATP phosphorylates motor proteinsMembraneproteinATPSoluteP iADP+Solute transported(b) Transport work: ATP phosphorylates transport proteinsGluNH3NH2(c) Chemical work: ATP phosphorylates key reactantsReactants: Glutamic acidand ammoniaProduct (glutamine)made+
21 Figure 8.12 The ATP cycle ATP synthesis from ADP + P i requires energy Energy for cellular work(endergonic, energy-consuming processes)Energy from catabolism(exergonic, energy yieldingprocesses)ATP hydrolysis toADP + P i yields energy
23 Figure 8.13 The effect of enzymes on reaction rate. Progress of the reactionProductsCourse ofreactionwithoutenzymeReactantswith enzymeEAEA withis lower∆G is unaffectedby enzymeFree energy
24 Figure 8.14 Induced fit between an enzyme and its substrate Active siteEnzyme(a)(b)Enzyme- substratecomplex
25 Figure 8.15 The active site and catalytic cycle of an enzyme 1 Substrates enter active site; enzymechanges shape so its active siteembraces the substrates (induced fit).SubstratesProductsEnzymeEnzyme-substratecomplex5 Products areReleased.2 Substrates held inactive site by weakinteractions, such ashydrogen bonds andionic bonds.3 Active site (and R groups ofits amino acids) can lower EAand speed up a reaction by• acting as a template forsubstrate orientation,• stressing the substratesand stabilizing thetransition state,• providing a favorablemicroenvironment,• participating directly in thecatalytic reaction.4 Substrates areConverted intoProducts.6 Active siteis available fortwo new substratemolecules.
26 Figure 8.16 Environmental factors affecting enzyme activity Optimal pH for two enzymesRate of reaction20406080100Temperature (Cº)(a) Optimal temperature for two enzymes(b) Optimal pH for two enzymespHOptimal temperature fortypical human enzymeenzyme of thermophilicOptimal pH for pepsin(stomach enzyme)Optimal pHfor trypsin(intestinalenzyme)12345678910(heat-tolerant)bacteria
29 Figure 8.17 Inhibition of enzyme activity Normal binding(b) Competitive inhibitionA substrate canbind normally to theactive site of anenzyme.A competitiveinhibitor mimics thesubstrate, competingfor the active site.SubstrateActive siteEnzymeNoncompetitive inhibitor(c) Noncompetitive inhibitionCompetitiveinhibitorA noncompetitiveinhibitor binds to theenzyme away fromthe active site, alteringthe conformation ofthe enzyme so that itsactive site no longerfunctions.
31 Figure 8.19 Allosteric regulation of enzyme activity Stabilized inactive formAllosteric activater stabilizes active fromAllosteric enyzme with four subunitsActive site (one of four)Regulatory site (one of four)Active formActivatorStabilized active formAllosteric activater stabilizes active formInhibitorInactive formNon- functional active site(a) Allosteric activators and inhibitors. In the cell, activators and inhibitors dissociate when at low concentrations. The enzyme can then oscillate again.Oscillation
32 Stabilized active form Binding of one substrate molecule to active site of one subunit locks all subunits in active conformation.SubstrateInactive formStabilized active form(b) Cooperativity: another type of allosteric activation. Note that the inactive form shown on the left oscillates back and forth with the active form when the active form is not stabilized by substrate.