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Metabolism, Photosynthesis, and Cellular Respiration

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Chapters 8, 9, and 10. Metabolism, Photosynthesis, and Cellular Respiration. Chapter 8. 8.1: An organism’s metabolism transforms the matter and energy, subject to the laws of thermodynamics Metabolism – totality of an organism’s chemical reactions - PowerPoint PPT Presentation

Text of Metabolism, Photosynthesis, and Cellular Respiration

Metabolism, Photosynthesis, and Cellular Respiration

Metabolism, Photosynthesis, and Cellular RespirationChapters 8, 9, and 10Chapter 88.1: An organisms metabolism transforms the matter and energy, subject to the laws of thermodynamicsMetabolism totality of an organisms chemical reactionsEmergent property of life that comes from molecular interactionsOrganization of the Chemistry of Life into Metabolic PathwaysMetabolic pathway begins with a specific molecule, molecule is altered in a series of steps, results in a specific productOne enzyme per step

StartingmoleculeACatabolic PathwaysDegradative processesRelease energyComplex molecules into simpler moleculesThink: CATs (CATabolic pathways) tear things apartAnabolic PathwaysConsume energySimpler molecules combined into a more complex oneSometimes called biosynthetic pathwaysExample: protein synthesis from amino acidsBioenergetics: study of how energy flows through living organismsForms of EnergyEnergy the capacity to cause changeThe ability to arrange a collection of matterCan be used to do workKinetic energy energy associated with the relative motion of objectsHeat (thermal energy) kinetic energy associated with the random movement of atoms or moleculesLight is also energyForms of EnergyPotential energy energy that is not kinetic; energy that matter possesses because of its location or structureChemical energy term used by biologists to refer to the potential energy available for release in a chemical reactionE.g. potential energy available through a catabolic reactionLaws of Energy TransformationThermodynamics the study of energy transformations that occur in a collection of matterSystems matter under studySurroundings everywhere outside of the systemIsolated system unable to exchange energy or matter with surroundingsOpen system exchanges energy and matter with surroundingsorganismsFirst Law of ThermodynamicsThe energy of the universe is constant Energy can be transferred and transformed, but it cannot be created or destroyedAlso known as the principle of conservation of energy Second Law of ThermodynamicsEvery energy transfer or transformation increases the entropy of the universeEntropy measure of disorder or randomnessSpontaneous process that can occur without input of energyMust increase entropy of the universeFor a process to occur spontaneously, it must increase the entropy of the universeBiological Order and DisorderLiving systems increase the entropy of their surroundingsOrdered structures created from less organized materialsCan go the other way as wellEntropy of a particular system can decrease, as long as the universe becomes more random at the same time8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneouslyFree-Energy Change, Delta GGibbs free energy, or free energy portion of s systems energy that can perform work when temperature and pressure are uniform throughout the system, as in a living cellDelta G = delta H TdeltaSDeltaH change in the systems enthalpy (equivalent to total energy)DeltaS - entropyFree Energy, Stability, and EquilibriumDeltaG = final G initial GNegative G is spontaneousTendency of a system to change to a more stable stateEquilibriumReversibleDoes not mean that forward and backward reactions stopSame rate or reaction, relative concentrations stay constantRefer to Figure 8.5Free Energy and MetabolismExergonic and Endergonic Reactions in MetabolismExergonic Energy outwardProceeds with a net release of free energyDeltaG is negativeEndergonicenergy inwardAbsorbs free energy from its surroundingDeltaG is positiveRefer to Figure 8.6

Equilibrium and MetabolismReactions in an isolated system would reach equilibrium and not be able to do any workA cell that has reached metabolic equilibrium is deadMetabolism as a whole is never at equilibrium8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactionsThree main kinds of workChemical work pushing of endergonic reactionsTransport work pumping of substances across membranes against the direction of spontaneous movementMechanical work actions such as beating of cilia, contracting of muscles, etc.Energy coupling the use of an exergonic reaction to power an endergonic oneATP usually responsibleThe Structure and Hydrolysis of ATPATP (adenosine triphosphate)Contains ribose, adenine, and three phosphate groupsOne of the nucleoside triphosphates used to make ATPBonds broken by hydrolysisATP + H2O ADP + HOPO32-High energy phosphate bondsHow ATP Performs WorkHydrolysis of ATP releases heatShiveringHeat usually harnessed to perform cellular workPhosphorylation the transfer of a phosphate group from ATP to some other molecule; the other molecule is now phosphorylatedTransport and mechanical work are nearly always powered by ATP hydrolysisLeads to a change in shape in the proteinThe Regeneration of ATP

ADPP+ATP+H2OEnergy fromcatabolism (exergonic,energy-releasingprocesses)Energy fromcatabolism (exergonic,energy-releasingprocesses)8.4: Enzymes speed up metabolic reactions by lowering energy barriersFigure 8.13Enzyme macromolecule that acts as a catalystCatalyst a chemical agent that speeds up a reaction without being consumed by the reactionThe Activation BarrierActivation energy (free energy of activation) The initial investment of energy for starting a reactionenergy required to contort reaction molecules so that they can breakOften supplied in the form of heat from surroundingsRefer to Figure 8.14How Enzymes Lower the EA BarrierFigure 8.15Heat can be used to speed up a reaction, but most organisms would die.Lowering the EA barrier enables the reactants to absorb enough energy to reach the transition state without reaching high temperatures.Substrate Specificity of EnzymesSubstrate the reactant an enzyme acts onForms an enzyme-substrate complex when the enzyme and substrate have joined togetherEnzyme + Substrate Enzyme-substrate complex Enzyme+ProductsMost enzyme names end in -aseSubstrate Specificity of EnzymesActive site region where the enzyme binds to the substrate; where catalysis occursInduced fit modelCatalysis in the Enzymes Active SiteFigure 8.17Occurs very quicklyReusable

Catalysis in the Enzymes Active SiteVariety of mechanisms to lower EAProvides template for substrates to come togetherEnzyme can stretch substrates to transition-state formActive site provides optimal microenvironmentDirect participation of active site in reactionRate related to initial substrate concentrationEffects of Local Conditions on Enzyme ActivityTemperaturepHChemicalsEffects of Temperature and pHUp to a point, ROR increases with temperatureOptimal pH value usually between 6 and 8Figure 8.18CofactorsCofactors nonprotein helpers for catalytic activityMay be tightly bound to enzyme permanently, or loosely bound with substrateInorganicCoenzyme cofactor that is an organic moleculevitaminsEnzyme InhibitorsCertain chemicals inhibit the action of specific enzymesTwo kinds:Competitive inhibitionBlock substrates from entering active sitesNoncompetitive inhibitionBind to another part of the enzyme so that it changes its shape, preventing the substrate from bindingFigure 8.198.5: Regulation of enzyme activity helps control metabolismREGULATION IS IMPORTANTAllosteric Regulation of EnzymesAllosteric regulation term used to describe any case in which a proteins function at one site is affected by the binding of a regulatory molecule to another siteLike reversible noncompetitive inhibitionFigure 8.20Allosteric Activation and Inhibition Enzymes made up of subunitsSubunits made up of polypeptide chainsThe binding of an activator stabilizes the active form of the enzymeThe binding of an inhibitor stabilizes the inactive form of the enzyme Identification of Allosteric RegulatorsNot that many metabolic enzymes are allosterically regulatedPharmaceutical companies interested in allosteric regulatorsExhibit higher specificity than do inhibitors binding to the active siteFigure 8.21Feedback InhibitionFeedback inhibition in which a metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme early in the pathwayFigure 8.22Specific Localization of Enzymes Within a CellThe cell is not a bag of chemicals with thousands of different kinds of enzymes and substrates in a random mix.Compartmentalized Chapter 9Cellular Respiration: Harvesting Chemical Energy9.1: Catabolic pathways yield energy by oxidizing organic fuelsThe breakdown of organic molecules is exergonicFermentation a partial degradation of sugars that occurs without O2Aerobic respiration consumes organic molecules and O2 and yields ATPAnaerobic respiration is similar to aerobic respiration but consumes compounds other than O2

Cellular RespirationContains both aerobic and anaerobic processes, but usually used to refer to aerobic respirationC6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)The breakdown of glucose is exergonicRedox ReactionsOxidation and ReductionReleases energy stored in organic moleculesLEO the lion says GER Oxidizing agent gets reduced, and reducing agent gets oxidizedChanging of electron sharing as opposed to transferring

Stepwise Energy Harvest via NAD+ and the Electron Transport ChainIn cellular respiration, glucose and other organic molecules are broken down in a series of stepsElectrons from organic compounds are usually first transferred to NAD+, a coenzymeAs an electron acceptor, NAD+ functions as an oxidizing agent during cellular respirationEach NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP

Electrons passed to ETC by NADHSeries of steps instead of all at once Stages of Cellular RespirationGlycolysis breaks down glucose into two molecules of pyruvateThe citric acid cycle completes the breakdown of glucoseOxidative phosphorylation -most of the ATP synthesis

9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvateGlycolysis means sugar splittingGlucose (six-carbon sugar) is split into two three-carbon sugarsSmaller sugars oxidizedRemaining molecules turned into pyruvate

GlycolysisOccurs in the cytoplasmDivided into:Energy investment Cell spends ATPEnergy payoff ATP is produced with substrate-level phosphorylation and NAD+ is reduced to NADHFigure 9.99.3: The citric acid cycle completes the energy yielding oxidation of organic moleculesPyruvate enters mitochondrion Must be converted to acetyl coenzyme A (acetyl CoA) before the citric acid cycle can beginFigure 9.10Citric acid cycle also called the Krebs cycle or the tricarboxylic acid cycleThe Citric Acid CycleTakes place within the mitochondrial matrixFigure 9.11Figure 9.12