12A diver has more potential energy on the platform than in the water. Fig. 8-2A diver has more potentialenergy on the platformthan in the water.Diving convertspotential energy tokinetic energy.Figure 8.2 Transformations between potential and kinetic energyClimbing up converts the kineticenergy of muscle movementto potential energy.A diver has less potentialenergy in the waterthan on the platform.
16(a) First law of thermodynamics (b) Second law of thermodynamics Fig. 8-3HeatCO2+ChemicalenergyH2OFigure 8.3 The two laws of thermodynamics(a) First law of thermodynamics(b) Second law of thermodynamics
24Fig. 8-5 More free energy (higher G) Less stable Greater work capacity In a spontaneous changeThe free energy of the systemdecreases (∆G < 0)The system becomes morestableThe released free energy canbe harnessed to do workLess free energy (lower G)More stableLess work capacityFigure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change(a) Gravitational motion(b) Diffusion(c) Chemical reaction
25More free energy (higher G) Less stable Greater work capacity Fig. 8-5aMore free energy (higher G)Less stableGreater work capacityIn a spontaneous changeThe free energy of the systemdecreases (∆G < 0)The system becomes morestableThe released free energy canbe harnessed to do workFigure 8.5 The relationship of free energy to stability, work capacity, and spontaneous changeLess free energy (lower G)More stableLess work capacity
26(a) Gravitational motion (b) Diffusion (c) Chemical reaction Fig. 8-5bSpontaneouschangeSpontaneouschangeSpontaneouschangeFigure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change(a) Gravitational motion(b) Diffusion(c) Chemical reaction
29Progress of the reaction Fig. 8-6ReactantsAmount ofenergyreleased(∆G < 0)EnergyFree energyProductsProgress of the reaction(a) Exergonic reaction: energy releasedProductsFigure 8.6 Free energy changes (ΔG) in exergonic and endergonic reactionsAmount ofenergyrequired(∆G > 0)EnergyFree energyReactantsProgress of the reaction(b) Endergonic reaction: energy required
30Amount of energy released (∆G < 0) Fig. 8-6aReactantsAmount ofenergyreleased(∆G < 0)Free energyEnergyProductsFigure 8.6a Free energy changes (ΔG) in exergonic and endergonic reactionsProgress of the reaction(a) Exergonic reaction: energy released
31Amount of energy required (∆G > 0) Fig. 8-6bProductsAmount ofenergyrequired(∆G > 0)EnergyFree energyReactantsFigure 8.6b Free energy changes (ΔG) in exergonic and endergonic reactionsProgress of the reaction(b) Endergonic reaction: energy required
33Fig. 8-7 ∆G < 0 ∆G = 0 (a) An isolated hydroelectric system (b) An open hydroelectricsystem∆G < 0Figure 8.7 Equilibrium and work in isolated and open systems∆G < 0∆G < 0∆G < 0(c) A multistep open hydroelectric system
34(a) An isolated hydroelectric system Fig. 8-7a∆G < 0∆G = 0Figure 8.7a Equilibrium and work in isolated and open systems(a) An isolated hydroelectric system
35(b) An open hydroelectric system Fig. 8-7b∆G < 0Figure 8.7b Equilibrium and work in isolated and open systems(b) An open hydroelectric system
36(c) A multistep open hydroelectric system Fig. 8-7c∆G < 0∆G < 0∆G < 0Figure 8.7c Equilibrium and work in isolated and open systems(c) A multistep open hydroelectric system
43∆G = +3.4 kcal/mol Glutamic acid Ammonia Glutamine Fig. 8-10NH2NH3+∆G = +3.4 kcal/molGluGluGlutamicacidAmmoniaGlutamine(a) Endergonic reaction1ATP phosphorylatesglutamic acid,making the aminoacid less stable.P+ATP+ADPGluGluNH2P2Ammonia displacesthe phosphate group,forming glutamine.NH3++PiGluGluFigure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis(b) Coupled with ATP hydrolysis, an exergonic reaction(c) Overall free-energy change
45Membrane protein Solute Solute transported Vesicle Cytoskeletal track Fig. 8-11Membrane proteinPPiSoluteSolute transported(a) Transport work: ATP phosphorylatestransport proteinsADPATP+PiVesicleCytoskeletal trackFigure 8.11 How ATP drives transport and mechanical workATPMotor proteinProtein moved(b) Mechanical work: ATP binds noncovalentlyto motor proteins, then is hydrolyzed
47+ H2O Energy for cellular work (endergonic, energy-consuming Fig. 8-12ATP+H2OEnergy fromcatabolism (exergonic,energy-releasingprocesses)Energy for cellularwork (endergonic,energy-consumingprocesses)Figure 8.12 The ATP cycleADP+Pi
49Sucrose (C12H22O11) Sucrase Glucose (C6H12O6) Fructose (C6H12O6) Fig. 8-13Sucrose (C12H22O11)SucraseFigure 8.13 Example of an enzyme-catalyzed reaction: hydrolysis of sucrose by sucraseGlucose (C6H12O6)Fructose (C6H12O6)
53Progress of the reaction Fig. 8-15Course ofreactionwithoutenzymeEAwithoutenzymeEA withenzymeis lowerReactantsFree energyCourse ofreactionwith enzyme∆G is unaffectedby enzymeFigure 8.15 The effect of an enzyme on activation energyProductsProgress of the reaction
57Substrates enter active site; enzyme Fig. 8-17Substrates enter active site; enzymechanges shape such that its active siteenfolds the substrates (induced fit).1Substrates held inactive site by weakinteractions, such ashydrogen bonds andionic bonds.2SubstratesEnzyme-substratecomplexActive site can lower EAand speed up a reaction.3Activesite isavailablefor two newsubstratemolecules.6Figure 8.17 The active site and catalytic cycle of an enzymeEnzyme5Products arereleased.Substrates areconverted toproducts.4Products
60Optimal temperature for typical human enzyme Optimal temperature for Fig. 8-18Optimal temperature fortypical human enzymeOptimal temperature forenzyme of thermophilic(heat-tolerant)bacteriaRate of reaction20406080100Temperature (ºC)(a) Optimal temperature for two enzymesOptimal pH for pepsin(stomach enzyme)Optimal pHfor trypsin(intestinalenzyme)Figure 8.18 Environmental factors affecting enzyme activityRate of reaction12345678910pH(b) Optimal pH for two enzymes
67Fig. 8-20 Figure 8.20 Allosteric regulation of enzyme activity Allosteric enyzmewith four subunitsActive site(one of four)Regulatorysite (oneof four)ActivatorActive formStabilized active formOscillationNon-functionalactivesiteInhibitorInactive formStabilized inactiveformFigure 8.20 Allosteric regulation of enzyme activity(a) Allosteric activators and inhibitorsSubstrateInactive formStabilized activeform(b) Cooperativity: another type of allosteric activation
68Stabilized active form Fig. 8-20aAllosteric enzymewith four subunitsActive site(one of four)Regulatorysite (oneof four)ActivatorActive formStabilized active formOscillationFigure 8.20a Allosteric regulation of enzyme activityNon-functionalactivesiteInhibitorInactive formStabilized inactiveform(a) Allosteric activators and inhibitors
70(b) Cooperativity: another type of allosteric activation Fig. 8-20bSubstrateInactive formStabilized activeformFigure 8.20b Allosteric regulation of enzyme activity(b) Cooperativity: another type of allosteric activation
72Hypothesis: allosteric inhibitor locks enzyme in inactive form Fig. 8-21EXPERIMENTCaspase 1ActivesiteSubstrateSHSHKnown active formActive form canbind substrateAllostericbinding siteSHS–SAllostericinhibitorKnown inactive formHypothesis: allostericinhibitor locks enzymein inactive formFigure 8.21 Are there allosteric inhibitors of caspase enzymes?RESULTSCaspase 1InhibitorActive formAllostericallyinhibited formInactive form
73EXPERIMENT Allosteric binding site Allosteric inhibitor Caspase 1 Fig. 8-21aEXPERIMENTCaspase 1ActivesiteSubstrateSHSHKnown active formActive form canbind substrateFigure 8.21 Are there allosteric inhibitors of caspase enzymes?Allostericbinding siteSHS–SAllostericinhibitorKnown inactive formHypothesis: allostericinhibitor locks enzymein inactive form
74RESULTS Caspase 1 Inhibitor Active form Allosterically inhibited form Fig. 8-21bRESULTSCaspase 1InhibitorFigure 8.21 Are there allosteric inhibitors of caspase enzymes?Active formAllostericallyinhibited formInactive form
76Fig. 8-22 Initial substrate (threonine) Active site available in active siteEnzyme 1(threoninedeaminase)Isoleucineused up bycellIntermediate AFeedbackinhibitionEnzyme 2Active site ofenzyme 1 nolonger bindsthreonine;pathway isswitched off.Intermediate BEnzyme 3Intermediate CFigure 8.22 Feedback inhibition in isoleucine synthesisIsoleucinebinds toallostericsiteEnzyme 4Intermediate DEnzyme 5End product(isoleucine)
78Living Organisms and Order How do living organisms create macromolecules, organelles, cells, tissues, and complex higher-order structures?A The laws of thermodynamics do not apply to living organisms.B Living organisms create order by using energy from the sun.C Living organisms create order locally, but the energy transformations generate waste heat that increases the entropy of the universe.Answer: cThis question relates to Concept 8.1.
79A the change in enthalpy (ΔH) is negative. Free Energy, Enthalpy, and Entropy When sodium chloride (table salt) crystals dissolve in water, the temperature of the solution decreases. This means that, for dissociation of Na+ and Cl– ions,A the change in enthalpy (ΔH) is negative.B the change in enthalpy (ΔH) is positive, but the change in entropy is greater.C the reaction is endergonic, because it absorbs heat.D the reaction must be coupled to an exergonic reaction.E the reaction cannot occur spontaneously.Answer: bThis question relates to Concept 8.2.
80Life and Chemical Equilibrium Are chemical reactions at equilibrium in living cells? yesnoonly the exergonic reactionsall reactions except those powered by ATP hydrolysisAnswer: bThis question relates to Concept 8.2. At equilibrium, the free energy change is zero, and no work can be done. A cell at equilibrium is dead!
81Free Energy A reaction has a ∆G of -5. 6 kcal/mol Free Energy A reaction has a ∆G of -5.6 kcal/mol. Which of the following would most likely be true?A The reaction could be coupled to power an endergonic reaction with a ∆G of +8.8 kcal/mol.B The reaction would result in an increase in entropy (S) and a decrease in the energy content (H) of the system.C The reaction would result in products with a greater free-energy content than in the initial reactants.Answer: cThis question relates to Concepts 8.2 and 8.3.
82B There is too much CO2 in the air. Rate of a Chemical Reaction The oxidation of glucose to CO2 and H2O is highly exergonic: ΔG = –636 kcal/mole. Why doesn’t glucose spontaneously combust?A The glucose molecules lack the activation energy at room temperature.B There is too much CO2 in the air.C CO2 has higher energy than glucose.D The formation of six CO2 molecules from one glucose molecule decreases entropy.E The water molecules quench the reaction.Answer: aThis question relates to Concept 8.4.
83Enzymes Firefly luciferase catalyzes the reaction luciferin + ATP ↔ adenyl-luciferin + pyrophosphate then the next reaction occurs spontaneously: adenyl-luciferin + O2 → oxyluciferin + H2O + CO2 + AMP + light What is the role of luciferase?A Luciferase makes the ΔG of the reaction more negative.B Luciferase lowers the transition energy of the reaction.C Luciferase alters the equilibrium point of the reaction.D Luciferase makes the reaction irreversible.E all of the aboveAnswer: bThis question relates to Concept 8.4.
84Enzyme-Catalyzed Reactions In the energy diagram below, which of the lettered energy changes would be the same in both the enzyme-catalyzed and uncatalyzed reactions?ABCDEAnswer: cThis question relates to Concept 8.4.
85A competitive inhibitors. B noncompetitive inhibitors. Enzyme Inhibitors Vioxx and other prescription non-steroidal anti-inflammatory drugs (NSAIDs) are potent inhibitors of the cycloxygenase-2 (COX-2) enzyme. High substrate concentrations reduce the efficacy of inhibition by these drugs. These drugs areA competitive inhibitors.B noncompetitive inhibitors.C allosteric regulators.D prosthetic groups.E feedback inhibitors.Answer: aThis question relates to Concepts 8.4 and 8.5.Sources:Copeland et al. Mechanism of Selective Inhibition of the Inducible Isoform of Prostaglandin G/H Synthase 1994, PNAS 91:Chan et al. Rofecoxib [Vioxx, MK-0966; 4-(4'-Methylsulfonylphenyl)-3-phenyl-2-(5H)-furanone]: A Potent and Orally Active Cyclooxygenase-2 Inhibitor. Pharmacological and Biochemical Profiles 1999, Pharmacology 290:
86Enzyme Regulation Adenosine monophosphate (AMP) activates the enzyme phosphofructokinase (PFK) by binding at a site distinct from the substrate binding site. This is an example ofA cooperative activation.B allosteric activation.C activation by an enzyme cofactor.D coupling exergonic and endergonic reactions.Answer: bThis question relates to Concept 8.5.