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  • Q: Given single and double bonds, which do you suppose requires more energy to break?
  • Q: How much work energy is available in a reaction in equilibrium? - 0
  • Q: What happens to the energy? - it needs to be focused
  • Q: What reaction do you know of that would be classified as redox? - NaCl


  • 1. EnergyTransformationATP Hydrolysis & CouplingATP Synthesis & RedoxThermochemistry
  • 2. Types of EnergyEnergy: capacity to do workExamples:KineticElectricNuclearSoundThermalGravitationalChemical
  • 3. PotentialEnergy Energy that matter possesses becauseof its location or structure Applied to many types of energy Example: gravitational potential energy Biological importance: Chemical energy is a form of potentialenergy in molecules because of thearrangement of atoms
  • 4. EnergyThe greater the bondenergy, the morechemically stable thebond.Bond stability is notrelated to chemicalreactivity.Bond Type Average BondEnergy (kJ/mol)H-H 436C-H 411O-H 459N-H 391C-C 346C-O 359C=O 799O=O 494
  • 5. ThermodynamicsThermodynamics: study of energytransformationsSystem: the matter under studySurroundings: everything outside the systemClosed system: isolated from its surroundingsOpen system: energy (and often matter) can betransferred between the system andsurroundingsExample: Organisms absorb energy in organicmolecules and release heat and metabolic wasteproducts
  • 6. First Law of ThermodynamicsThe total amount of energy in the universe isconstant.Thus energy cannot be created or destroyed.Energy can be transferred and transformed,converting from one form to another
  • 7. Energy Transformation ExampleExample: Climbing a slide &sliding downConverting kinetic energy topotential energy back to kineticenergyQuestion: Where did the initialkinetic energy for climbingcome from?Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 8. Energy Transformation Answer: From potentialenergy in food eaten earlierthat was stored in the body Cellular respiration unleashesthe potential energy in thefoods that we consume
  • 9. Energy Transformation Q: Where did the chemical energy in food come from? A: From light energy by plants during photosynthesis
  • 10. Energy Transformation Sunlight provides a dailysource of free energy for thephotosynthetic organisms. Plants transform light tochemical energy; they do notproduce energy. Nonphotosyntheticorganisms depend on atransfer of free energy fromphotosynthetic organisms inthe form of organicmolecules.Light energyECOSYSTEMCO2 + H2OPhotosynthesisin chloroplastsCellular respirationin mitochondriaOrganicmolecules+ O2ATPpowers most cellular workHeatenergyFigure 9.1
  • 11. Energy TransformationThe quantity of energyis constant, but thequality is not.Organisms take inorganized energy likelight or organicmolecules and replacethem with less orderedforms, especially heat.Light energyECOSYSTEMCO2 + H2OPhotosynthesisin chloroplastsCellular respirationin mitochondriaOrganicmolecules+ O2ATPpowers most cellular workHeatenergyFigure 9.1
  • 12. Second Law of ThermodynamicsEnergy transformation make the universe moredisordered.Example: C6H12O6 + O2  CO2 + H2O + energyEntropy: a measure of disorder, chaos, orrandomnessAlthough order can increase locally in a particularsystem, it requires the input of energy and theuniverse will still trend towards randomization.Example: CO2 + H2O + energy  C6H12O6 + O2
  • 13. HeatEnergy of random molecular motion; energy in itsmost random stateMuch of the increased entropy of universe takesthe form of increasing heatLiving cells unavoidably convert organized forms ofenergy to heat.The metabolic breakdown of food ultimately isreleased as heat even if some of it is divertedtemporarily to perform work for the organism.
  • 14. Gibbs Free EnergyThe energy that is able to perform workΔG = Gfinal – Ginitial = Gproducts - GreactantsCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 15. Exergonic EndergonicGibbs Free EnergyCharacteristics Exergonic EndergonicEnergy Released AbsorbedΔG Negative PositiveReaction Spontaneous NonspontaneousProducts More stabile, less energy Less stable, more energyCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 16. Cellular EnergyEnergy transfer in a cell depends on bond energyAll chemical reactions break and form bonds:Breaking bonds require energyForming bonds releases energyThe net energetic effect of the reaction:Exergonic when energy for breaking bonds is lessthan formingEndergonic when energy for breaking bonds is morethan forming
  • 17. Cellular EnergyCharacteristics Exergonic EndergonicEnergy Released AbsorbedΔG Negative PositiveReaction Spontaneous NonspontaneousProductsMore stabileLess energyLess stableMore energyBond energy Breaking < forming Breaking > forming
  • 18. Cellular Energy Cellular respiration: C6H12O6 + O2  CO2 + H2O + energy Photosynthesis: CO2 + H2O + energy  C6H12O6 + O2Example Cellular Respiration PhotosynthesisEnergy Released AbsorbedΔG-2870 kJ/mol-686 kcal/mol+2870 kJ/mol+686 kcal/molReaction Spontaneous NonspontaneousClassification Exergonic Endergonic
  • 19. Equilibrium A system at equilibrium is at maximum stability. Equilibrium reactions convert back and forth with minimalenergy. ΔG = 0 Example: In a chemical reaction, the rate of forward andbackward reactions are equal. There is no change in theconcentration of products or reactants.
  • 20. EquilibriumReactions in closed systems eventually reachequilibrium and can do no work.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 21. EquilibriumCells are open systems which maintainsdisequilibriumA cell that has reached metabolic equilibrium hasa ΔG = 0 and is dead!Metabolic disequilibrium is one of the definingfeatures of lifeCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 22. Adenosine Triphosphate (ATP)In most cases, the immediate source of energythat powers cellular work is ATPCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 23. ATP HydrolysisHydrolysis releases the end phosphate group:ATP  ADP + PiΔG is -7.3 kcal/mol under standard conditionsΔG is -13 kcal/mol in a cellCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 24. Phosphate BondsReferred to as high-energy phosphate bonds butare actually fairly weak covalent bondsEach of the three phosphate groups has a negativechargeTheir repulsion contributes to the instability of thisregion of the ATP molecule.Their hydrolysis yields energy as the products aremore stable
  • 25. CouplingEnergy from thehydrolysis of ATP iscoupled toendergonic processesby transferring thephosphate group toanother molecule.The phosphorylatedmolecule is now morereactive.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 26. Types of Cellular Work Transport work pumping substances acrossmembranes against the direction ofspontaneous movement Mechanical work beating of cilia contraction of muscle cells movement of chromosomes Chemical work driving endergonic reactions such asthe synthesis of polymers frommonomersFig 9.2
  • 27. ATP Coupling and workFigure 9.2
  • 28. ATP CouplingATP hydrolysis does not occur on its own.Process is carried out with enzymes that can transferthe phosphate
  • 29. ATP SynthesisATP is continually regenerated by adding aphosphate group to ADPIn a working muscle cell the entire pool of ATP isrecycled once each minuteOver 10 million ATP consumed and regenerated persecond per cellCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 30. ATP SynthesisRegeneration of ATP is an endergonic process:investment of energy: ΔG = +7.3 kcal/molEnergy for renewal comes from catabolicreactions in the cellRelocation of electrons in organic compoundsreleases chemical potential energy to drivesynthesis of ATPCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
  • 31. Methods of ATP SynthesisSubstrate-level phosphorylationOxidative phosphorylation
  • 32. Substrate-level PhosphorylationDirect method of ATP synthesisFood
  • 33. Substrate-level Phosphorylation An enzyme transfers phosphatefrom substrate to ADP Example from glycolysis incellular respiration(Pyruvate Kinase)
  • 34. Oxidative PhosphorylationIndirect method of ATP synthesisUses redox reactions where electrons aretransferred to an intermediate forming highenergy molecules (NADH, FADH2)NADHFoodElectrontransport chainNAD+
  • 35. Redox Reactionsreactions involving electron transfer
  • 36. The Principle of Redox Oxidation A substance loses electrons Is oxidized Reduction A substance gains electrons Is reduced Loss of Electrons is Oxidation Gain of Electron is ReductionLEO the lion says GER
  • 37. Redox ReactionsReducing Agent:substance that LOSES electronscauses the other substance to be reducedOxidizing Agent:substances that GAIN electronscauses the other substance to be oxidized
  • 38. Examples of Redox ReactionsNa + Cl Na++ Cl–becomes oxidized(loses electron)becomes reduced(gains electron)Xē + Y X + Yēbecomes oxidizedbecomes reducedWe could generalize a redox reaction this way:X is the electron donor, is called the reducing agent, it reduces Y which accepts the donated electronY is the electron acceptor, it oxidizes X by removing its electron is the reducing agent
  • 39. Redox and ElectronegativitySome redox reactionsdo not completelyexchange electronsChange the degree ofelectron sharing incovalent bondsAn electron losespotential energy whenit shifts from a lesselectronegative atomtoward moreelectronegative oneCH4HHHHC O O O O OCH HMethane(reducingagent)Oxygen(oxidizingagent)Carbon dioxide Water+ 2O2 CO2 + Energy + 2 H2Obecomes oxidizedbecomes reducedReactants ProductsFigure 9.3
  • 40. Redox in Cellular RespirationOxidation ofmethane is the maincombustion reactionthat occurs at theburner of a gas stoveReplace equationwith glucose to getthe equation forcellular respirationCH4HHHHC O O O O OCH HMethane(reducingagent)Oxygen(oxidizingagent)Carbon dioxide Water+ 2O2 CO2 + Energy + 2 H2Obecomes oxidizedbecomes reducedReactants ProductsFigure 9.3
  • 41. Redox in Cellular RespirationGlucose is oxidized and oxygen is reducedOrganic molecules are excellent fuels becausetheir hydrogens are a source of electrons with apotential to “fall” closer to oxygenC6H12O6 + 6O2 6CO2 + 6H2O + Energybecomes oxidizedbecomes reduced
  • 42. Oxidizing Agent in MetabolismNAD+Nicotinamide adenine dinucleotidea coenzymeaccept electrons from organiccompounds forming NADHacts as an oxidizing agent
  • 43. Redox with NAD+/NADHNAD ++ e- NADH (electron carrier)
  • 44. NAD+HOOO O–OO O–OOOPPCH2CH2HO OHHHHO OHHOHHN+C NH2HNHNH2NNNicotinamide(oxidized form)NH2+ 2[H](from food)DehydrogenaseReduction of NAD+Oxidation of NADH2 e–+ 2 H+2 e–+ H+NADHOH HNC +Nicotinamide(reduced form)NH+H+Figure 9.4Redox with NAD+/NADH Dehydrogenase enzyme removes a pair of hydrogenatoms (2 electrons and 2protons) from the substrate (eg.sugar) 2 electrons and 1 H+ stay onnicotinamide leaving 1 H+
  • 45. Oxidative PhosphorylationIndirect method of ATP SynthesisFood  NADH  ATP  WorkNADHFoodElectrontransport chainNAD+Reduction Oxidation
  • 46. Reducing Agent in MetabolismEach NADH molecule represents stored energythat can make ATPWhen electrons in NADH fall down an energygradient to oxygen, the exergonic reactionreleases a free energy change of – 53 kcal/molOccurs in the mitochondria through a processcalled the electron transport chain (ETC)Oxygen is the final electron acceptor
  • 47. Redox in the CellMany metabolic processes consist of chains ofredox reactions.A-AB-BC-C DD-
  • 48. Harnessing Free EnergyWholesale releaseof energy from fuelis difficult toharness efficientlyfor workExample: explosionof a gas tank can’tdrive a car
  • 49. Harnessing Free EnergyCells release free energy by gradually breakingdown organic fuel in a series of reactions eachcatalyzed by an enzymeHydrogens are taken from organic fuelSome are transferred first to a coenzyme (NAD+)before going to oxygen
  • 50. Electron Transport Chain (ETC)Consists of a number ofproteins that aid withthe transfer ofelectrons, thuscontrolling the releaseof energy for ATPsynthesisCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings2 H 1/2 O2(from food via NADH)2 H++ 2 e–2 H+2 e–H2O1/2 O2Controlledrelease ofenergy forsynthesis ofATPATPATPATPElectrontransportchainFreeenergy,G+Figure 9.5 BOrganic fuel NADH ETC Oxygen→ → →
  • 51. If electron transfer is not stepwise…A large release of energy occursExample: Oxidation of sugarExample: Reaction of hydrogen andoxygen to form water reactionFigure 9.5 AFreeenergy,GH2OExplosiverelease ofheat and lightenergyH2 + 1/2 O2
  • 52. Food & Activation EnergyMain energy foods are reservoirs of electronsassociated with hydrogenActivation energy is the barrier that preventselectrons from falling to a lower energy stateWithout it, food substances would combinespontaneously with oxygen
  • 53. Demo: Food & Activation EnergySupply activation energy to glucose by igniting itReleases 686 kcal of heat per mole