Cellular Respiration: Harvesting Chemical Energy

Chapter 9Cellular Respiration:Harvesting Chemical EnergyPowerPoint Lecture Presentations forBiologyEighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan SharpCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Overview: Life Is Work Living cells require energy from outsidesources Some animals, such as the giant panda, obtainenergy by eating plants, and some animalsfeed on other organisms that eat plantsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-1

Energy flows into an ecosystem as sunlightand leaves as heat Photosynthesis generates O2 and organicmolecules, which are used in cellularrespiration Cells use chemical energy stored in organicmolecules to regenerate ATP, which powersworkCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-2LightenergyECOSYSTEMPhotosynthesisin chloroplastsCO2 H2OOrganic Omolecules 2Cellular respirationin mitochondriaATPATP powers most cellular workHeatenergy

Concept 9.1: Catabolic pathways yield energy byoxidizing organic fuels Several processes are central to cellularrespiration and related pathwaysCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Catabolic Pathways and Production of ATP The breakdown of organic molecules isexergonic Fermentation is a partial degradation ofsugars that occurs without O2 Aerobic respiration consumes organicmolecules and O2 and yields ATP Anaerobic respiration is similar to aerobicrespiration but consumes compounds otherthan O2Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cellular respiration includes both aerobic andanaerobic respiration but is often used to referto aerobic respiration Although carbohydrates, fats, and proteins areall consumed as fuel, it is helpful to tracecellular respiration with the sugar glucose:C6H12O6 6 O2(ATP heat)6 CO2 6 H2O EnergyCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Redox Reactions: Oxidation and Reduction The transfer of electrons during chemicalreactions releases energy stored in organicmolecules This released energy is ultimately used tosynthesize ATPCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Principle of Redox Chemical reactions that transfer electronsbetween reactants are called oxidation-reductionreactions, or redox reactions In oxidation, a substance loses electrons, or isoxidized In reduction, a substance gains electrons, or isreduced (the amount of positive charge isreduced)Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-UN1becomes oxidized(loses electron)becomes reduced(gains electron)

Fig. 9-UN2becomes oxidizedbecomes reduced

The electron donor is called the reducingagent The electron receptor is called the oxidizingagent Some redox reactions do not transfer electronsbut change the electron sharing in covalentbonds An example is the reaction between methaneand O2Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-3ReactantsProductsbecomes oxidizedbecomes )Carbon dioxideWater

Oxidation of Organic Fuel Molecules DuringCellular Respiration During cellular respiration, the fuel (such asglucose) is oxidized, and O2 is reduced:Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-UN3becomes oxidizedbecomes reduced

Fig. 9-UN4Dehydrogenase

Stepwise Energy Harvest via NAD and the ElectronTransport Chain In cellular respiration, glucose and otherorganic molecules are broken down in a seriesof steps Electrons from organic compounds are usuallyfirst transferred to NAD , a coenzyme As an electron acceptor, NAD functions as anoxidizing agent during cellular respiration Each NADH (the reduced form of NAD )represents stored energy that is tapped tosynthesize ATPCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-42 e– 2 H 2 e– H NADHH DehydrogenaseReduction of NAD NAD H 2[H]Oxidation of NADHNicotinamide(reduced form)Nicotinamide(oxidized form)

NADH passes the electrons to the electrontransport chain Unlike an uncontrolled reaction, the electrontransport chain passes electrons in a series ofsteps instead of one explosive reaction O2 pulls electrons down the chain in an energyyielding tumble The energy yielded is used to regenerate ATPCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-5H2 1/2 O22H(from food via NADH)Controlledrelease of –2H 2eenergy forsynthesis ofATP1/2 O2Explosiverelease ofheat and lightenergy1/(a) Uncontrolled reaction(b) Cellular respiration2 O2

The Stages of Cellular Respiration: A Preview Cellular respiration has three stages:– Glycolysis (breaks down glucose into twomolecules of pyruvate)– The citric acid cycle (completes thebreakdown of glucose)– Oxidative phosphorylation (accounts formost of the ATP synthesis)Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-6-1Electronscarriedvia evelphosphorylation

Fig. 9-6-2Electrons carriedvia NADH andFADH2Electronscarriedvia Substrate-levelphosphorylation

Fig. 9-6-3Electrons carriedvia NADH andFADH2Electronscarriedvia ivephosphorylation:electron osphorylationOxidativephosphorylation

The process that generates most of the ATP iscalled oxidative phosphorylation because it ispowered by redox reactionsBioFlix: Cellular RespirationCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Oxidative phosphorylation accounts for almost90% of the ATP generated by cellularrespiration A smaller amount of ATP is formed inglycolysis and the citric acid cycle bysubstrate-level phosphorylationCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-7EnzymeEnzymeADPPSubstrate ProductATP

Concept 9.2: Glycolysis harvests chemical energyby oxidizing glucose to pyruvate Glycolysis (“splitting of sugar”) breaks downglucose into two molecules of pyruvate Glycolysis occurs in the cytoplasm and has twomajor phases:– Energy investment phase– Energy payoff phaseCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-8Energy investment phaseGlucose2 ADP 2 P2 ATPused4 ATPformedEnergy payoff phase4 ADP 4 P2 NAD 4 e– 4 H 2 NADH 2 H 2 Pyruvate 2 H2ONetGlucose4 ATP formed – 2 ATP used2 NAD 4 e– 4 H 2 Pyruvate 2 H2O2 ATP2 NADH 2 H

Fig. phateATP1HexokinaseADPGlucose-6-phosphate

Fig. e

Fig. kinaseADPADPFructose1, 6-bisphosphateFructose1, 6-bisphosphate

Fig. hosphoglucoisomeraseFructose1, sphofructokinaseADP5IsomeraseFructose1, hosphateGlyceraldehyde3-phosphate

Fig. 9-9-52 NAD 2 NADH 2 H 6Triose phosphatedehydrogenase2 Pi2 1, 3-BisphosphoglycerateGlyceraldehyde3-phosphate2 NAD 2 NADH6Triose phosphatedehydrogenase2 Pi 2 H 2 1, 3-Bisphosphoglycerate

Fig. 9-9-62 NAD 2 NADH 2 H 6Triose phosphatedehydrogenase2 Pi2 1, 3-Bisphosphoglycerate2 ADP7Phosphoglycerokinase2 ATP2 1, 3-Bisphosphoglycerate2 ADP23-Phosphoglycerate2 ATP27Phosphoglycerokinase3-Phosphoglycerate

Fig. 9-9-72 NAD 2 NADH 2 H 6Triose phosphatedehydrogenase2 Pi2 1, 3-Bisphosphoglycerate2 ADP7 Phosphoglycerokinase2 te22-Phosphoglycerate

Fig. 9-9-82 NAD 2 NADH 2 H 6Triose phosphatedehydrogenase2 Pi2 1, 3-Bisphosphoglycerate2 ADP7 Phosphoglycerokinase2 lyceromutase922 H2O2-PhosphoglycerateEnolase9Enolase2 H2O2Phosphoenolpyruvate2Phosphoenolpyruvate

Fig. 9-9-92 NAD 6Triose phosphatedehydrogenase2 Pi2 NADH 2 H 2 1, 3-Bisphosphoglycerate2 ADP7 Phosphoglycerokinase2 ATP2Phosphoenolpyruvate2 ADP23-Phosphoglycerate8Phosphoglyceromutase2 ATP210Pyruvatekinase2-Phosphoglycerate92 H2OEnolase2 Phosphoenolpyruvate2 ADP10Pyruvate kinase2 ATP22PyruvatePyruvate

Concept 9.3: The citric acid cycle completes theenergy-yielding oxidation of organic molecules In the presence of O2, pyruvate enters themitochondrion Before the citric acid cycle can begin, pyruvatemust be converted to acetyl CoA, which linksthe cycle to glycolysisCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-10CYTOSOLMITOCHONDRIONNAD NADH H 21PyruvateTransport protein3CO2Coenzyme AAcetyl CoA

The citric acid cycle, also called the Krebscycle, takes place within the mitochondrialmatrix The cycle oxidizes organic fuel derived frompyruvate, generating 1 ATP, 3 NADH, and 1FADH2 per turnCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-11PyruvateCO2NAD CoANADH H Acetyl CoACoACoACitricacidcycleFADH22 CO23 NAD 3 NADHFAD 3 H ADP P iATP

The citric acid cycle has eight steps, eachcatalyzed by a specific enzyme The acetyl group of acetyl CoA joins the cycleby combining with oxaloacetate, forming citrate The next seven steps decompose the citrateback to oxaloacetate, making the process acycle The NADH and FADH2 produced by the cyclerelay electrons extracted from food to theelectron transport chainCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-12-1Acetyl CoACoA—SH1OxaloacetateCitrateCitricacidcycle

Fig. 9-12-2Acetyl cacidcycle

Fig. 9-12-3Acetyl CoACoA—SH1H2OOxaloacetate2CitrateIsocitrateNAD Citricacidcycle3NADH H CO2-Ketoglutarate

Fig. 9-12-4Acetyl CoACoA—SH1H2OOxaloacetate2CitrateIsocitrateNAD CitricacidcycleNADH H 3CO2CoA—SH-Ketoglutarate4NAD SuccinylCoANADH H CO2

Fig. 9-12-5Acetyl CoACoA—SH1H2OOxaloacetate2CitrateIsocitrateNAD CitricacidcycleNADH H 3CO2CoA—SH-Ketoglutarate4CoA—SH5NAD SuccinateGTP GDPADPATPPiSuccinylCoANADH H CO2

Fig. 9-12-6Acetyl CoACoA—SHH2O1Oxaloacetate2CitrateIsocitrateNAD CitricacidcycleNADH H NAD FADSuccinateGTP GDPADPATPPiSuccinylCoANADH H CO2

Fig. 9-12-7Acetyl eNAD Citricacidcycle7H2ONADH H NAD FADSuccinateGTP GDPADPATPPiSuccinylCoANADH H CO2

Fig. 9-12-8Acetyl CoACoA—SHNADH H H2O1NAD 8Oxaloacetate2MalateCitrateIsocitrateNAD Citricacidcycle7H2ONADH H NAD FADSuccinateGTP GDPADPATPPiSuccinylCoANADH H CO2

Concept 9.4: During oxidative phosphorylation,chemiosmosis couples electron transport to ATPsynthesis Following glycolysis and the citric acid cycle,NADH and FADH2 account for most of theenergy extracted from food These two electron carriers donate electrons tothe electron transport chain, which powers ATPsynthesis via oxidative phosphorylationCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Pathway of Electron Transport The electron transport chain is in the cristae ofthe mitochondrion Most of the chain’s components are proteins,which exist in multiprotein complexes The carriers alternate reduced and oxidizedstates as they accept and donate electrons Electrons drop in free energy as they go downthe chain and are finally passed to O2, formingH 2OCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-13NADH502 e–NAD FADH22 e–40FADMultiproteincomplexesFADFMNFe SFe SQCyt b30Fe SCyt c1IVCyt cCyt aCyt a320102 e–(from NADHor FADH2)02 H 1/2 O2H2O

Electrons are transferred from NADH or FADH2to the electron transport chain Electrons are passed through a number ofproteins including cytochromes (each with aniron atom) to O2 The electron transport chain generates no ATP The chain’s function is to break the large freeenergy drop from food to O2 into smaller stepsthat release energy in manageable amountsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in the electron transport chaincauses proteins to pump H from themitochondrial matrix to the intermembrane space H then moves back across the membrane,passing through channels in ATP synthase ATP synthase uses the exergonic flow of H todrive phosphorylation of ATP This is an example of chemiosmosis, the use ofenergy in a H gradient to drive cellular workCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-14INTERMEMBRANE SPACEH StatorRotorInternalrodCatalyticknobADP PiATPMITOCHONDRIAL MATRIX