Chapter 8Organization of the Chemistry of Life into Metabolic PathwaysSlide 3The Laws of Energy TransformationThe Second Law of ThermodynamicsBiological Order and DisorderFree Energy, Stability, and EquilibriumExergonic ReactionEndergonic ReactionEquilibrium and MetabolismSlide 11The Structure and Hydrolysis of ATPHow ATP Performs WorkSlide 14Slide 15The Regeneration of ATPSlide 17How Enzymes Lower the EA BarrierSlide 19Catalysis in the Enzyme’s Active SiteThe catalytic cycle of an enzymeEffects of Temperature and pHHas an optimal pH in which it can functionEnzyme InhibitorsSlide 25Allosteric Activation and InhibitionFeedback InhibitionYou should now be able to:Slide 29PowerPoint Lectures for Biology, Eighth EditionNeil Campbell and Jane ReeceChapter 8Chapter 8An Introduction to MetabolismOrganization of the Chemistry of Life into Metabolic Pathways•A metabolic pathway has many steps–That begin with a specific molecule and end with a product–That are each catalyzed by a specific enzymeEnzyme 1 Enzyme 2 Enzyme 3ABCDReaction 1 Reaction 2 Reaction 3StartingmoleculeProduct•Energy can be converted from one form to anotherOn the platform, a diverhas more potential energy.Diving converts potentialenergy to kinetic energy.Climbing up converts kineticenergy of muscle movement to potential energy.In the water, a diver has less potential energy.Figure 8.2The Laws of Energy TransformationFirst law of thermodynamics: Energy can be transferred or transformed but Neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b).(a)ChemicalenergyThe Second Law of ThermodynamicsSecond law of thermodynamics: Every energy transfer or transformation increasesthe disorder (entropy) of the universe. For example, disorder is added to the cheetah’ssurroundings in the form of heat and the small molecules that are the by-productsof metabolism.(b)Heatco2H2O+Biological Order and Disorder50µm•At maximum stability, the system is at equilibriumChemical reaction. In a cell, a sugar molecule is broken down into simpler molecules. .Diffusion. Molecules in a drop of dye diffuse until they are randomly dispersed.Gravitational motion. Objectsmove spontaneously from ahigher altitude to a lower one.• More free energy (higher G)• Less stable• Greater work capacity• Less free energy (lower G)• More stable• Less work capacity In a spontaneously change • The free energy of the system decreases (∆G<0) • The system becomes more stable• The released free energy can be harnessed to do work (a)(b)(c)Figure 8.5 Free Energy, Stability, and Equilibrium•Proceeds with a net release of free energy and is spontaneousReactantsProductsEnergyProgress of the reactionAmount ofenergyreleased (∆G <0)Free energy(a) Exergonic reaction: energy releasedExergonic ReactionEndergonic Reaction•Is one that absorbs free energy from its surroundings and is non-spontaneousEnergyProductsAmount ofenergyreleased (∆G>0)ReactantsProgress of the reactionFree energy(b) Endergonic reaction: energy requiredEquilibrium and Metabolism•Reactions in a closed system eventually reach equilibrium(a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium.∆G < 0∆G = 0•Cells in our body experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium(b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium.∆G < 0The Structure and Hydrolysis of ATP•ATP (adenosine triphosphate)–Is the cell’s energy shuttle–Provides energy for cellular functionsOOOOCH2HOH OHHNH HONCHCNCCNNH2AdenineRibosePhosphate groupsOOOOOO-- - -CHHow ATP Performs WorkPAdenosine triphosphate (ATP)H2O+EnergyInorganic phosphateAdenosine diphosphate (ADP)PPP PP i•The three types of cellular work are powered by the hydrolysis of ATP(c) Chemical work: ATP phosphorylates key reactantsPMembraneprotein Motor proteinP iProtein moved(a) Mechanical work: ATP phosphorylates motor proteinsATP(b) Transport work: ATP phosphorylates transport proteinsSolutePP itransportedSoluteGluGluNH3NH2P iP i++Reactants: Glutamic acid and ammoniaProduct (glutamine)madeADP+P•ATP hydrolysis can be coupled to other reactionsEndergonic reaction: ∆G is positive, reaction is not spontaneous ∆G = +3.4 kcal/molGluGlu∆G = + 7.3 kcal/molATPH2O++NH3ADP+NH2GlutamicacidAmmoniaGlutamineExergonic reaction: ∆ G is negative, reaction is spontaneous PCoupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/molFigure 8.10The Regeneration of ATP•Catabolic pathways–Drive the regeneration of ATP from ADP and phosphateATP synthesis from ADP + P i requires energyATPADP + P iEnergy for cellular work(endergonic, energy-consuming processes)Energy from catabolism(exergonic, energy yieldingprocesses)ATP hydrolysis to ADP + P i yields energyFigure 8.12•The energy profile for an exergonic reactionFree energyProgress of the reaction∆G < OEAFigure 8.14ABCDReactantsACDBTransition stateABC DProductsProgress of the reactionProductsCourse of reaction without enzymeReactantsCourse of reaction with enzymeEAwithoutenzymeEA with enzymeis lower∆G is unaffected by enzymeFree energyFigure 8.15How Enzymes Lower the EA Barrier•An enzyme catalyzes reactions–By lowering the EA barrier•The active site is the region on the enzyme where the substrate bindsSubstateActive siteEnzyme(a)•Induced fit of a substrate(b)Enzyme- substratecomplexCatalysis in the Enzyme’s Active SiteThe catalytic cycle of an enzymeSubstratesProductsEnzymeEnzyme-substratecomplex 1 Substrates enter active site; enzymechanges shape so its active siteembraces the substrates (induced fit). 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 for substrate orientation,• stressing the substrates and stabilizing the transition state,• providing a favorable microenvironment,• participating directly in the catalytic reaction.4 Substrates are Converted intoProducts.5 Products areReleased.6 Active siteIs available fortwo new
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