10 Cellular Respiration

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Chapter 9

Cellular RespirationSome intermediates feed into other pathwaysCatabolic pathways provide building block molecules and energy for anabolic pathwaysMetabolic Pathways

energyenergyParticipants in Metabolic Pathways

NAD+hexokinasephosphoglucose isomerasephosphofructokinaseReactant (substrate)IntermediatesProductParticipants in Metabolic Pathways

NAD+hexokinasephosphoglucose isomerasephosphofructokinaseEnzymesCofactorsCoenzymesCellular Respiration & Photosynthesis

PHOTOSYNTHESISenergy-capturingCELLULAR RESPIRATIONenergy-releasing6O2 + 6CO2 + 6H2OSOLARENERGYC6H12O6ATPchemical energyglucoseWhich process is exergonic?

Which process is anabolic?Glucose:Hub of Energy Processing in Cells

Glucose production (anabolism) and storage

Glucose:Hub of Energy Processing in Cells

Breakdown of glucose (catabolism) for energyCellular RespirationCellular Respiration process by which cells produce ATP from a nutrient molecule (usually glucose) with high potential energyStep-wise release of energy from glucoseRequires O2Glucose is broken down (catabolized) to CO2 and H2OGlucose is oxidized to CO2Exergonic process (net)Released energy is used to make ATP (from ADP + Pi)

4 connected pathwaysGlycolysisPyruvate processing (prep rxn)Citric acid (Krebs) cycleElectron transport chain/chemiosmosis2 types of electron carriers2 compartments2 types of ATP synthesisCell Respiration

9ATP Cycle: Renewing Supplies of ATPEnergy from EXERGONIC reactions(e.g. cellular respiration)

Energy for ENDERGONIC reactions(e.g. protein synthesis, muscle contraction)Making ATPATP is produced using the energy stored in organic molecules (chemical energy; potential energy) such as glucose

One way of transferring energy is through the transfer of electronsElectrons and energy transferred to molecule BMethods of Producing ATPSubstrate-Level Phosphorylation enzyme catalyzes transfer of phosphate group from phosphorylated substrate to ADP (to make ATP)

Oxidative Phosphorylation (Electron Transport & Chemiosmosis) oxidation of NADH and FADH2 and electron transport produces proton gradient, which drives ATP synthesis (phosphorylation of ADP)

EnzymeADPATPPhosphorylatedsubstrateMethods of Producing ATPsubstrate-level phosphorylationoxidative phosphorylation

CytosolElectronsElectron transport chainGlycolysisSteps 1-3 (energy investment)Start with one glucose (hexose sugar) Rearrange structureAdd phosphate groupsSteps 4 & 5 (sugar splitting)Split hexose in halfBoth halves used in subsequent rxnsSteps 6-10 (energy harvest)Rearrange structure & remove phosphatesEnd with two pyruvates (3-carbon organic acid)

Glycolysis What goes in and what comes out

What comes out:What goes in:All 10 reactionsof glycolysisoccur in cytosolGlycolysis begins with anenergy-investmentphase: 2 ATP 2 ADPEnzymeGlucose-6-phosphateFructose-6-phosphateFructose-1,6-bisphosphateGlucose

PyruvateThe 2 indicates that glucosehas been split into two 3-carbonsugars (only one is shown)During the energy payoff phase, 4 ATPare produced for a net gain of 2 ATPSubstrate-level phosphorylationsGlycolysis What goes in and what comes outGlycolysisTracking Carbon and EnergyCarbonInputs: 1 glucose (6-C)Outputs: 2 pyruvate (3-C each)

EnergyInputs:potential energy contained in chemical bonds in glucose2 ATPOutputs:potential energy in bonds in pyruvate (less than in glucose)4 ATP (Net: 2 ATP)2 NADH (carry electrons/energy)Regulation of Glycolysis

GlucoseGlucose-6-phosphateFructose-6-phosphateFructose-1,6-bisphosphatePFKCommitted Stepcatalyzed by phosphofructokinase (PFK)PFK is inhibited by ATPATPFeedback InhibitionFeedback Inhibition an enzyme in a metabolic pathway is inhibited by the product of the reaction sequence

Why is feedback inhibition beneficial?

AllostericsiteFructose-1,6-bisphosphateat active siteATP/ADP atactive siteRegulation of Glycolysis: PFK

Fructose-6-phosphateFructose-1,6-bisphosphatePFKATPPFK has two binding sites for ATPActive site ATP as substrateAllosteric site ATP as allosteric inhibitorCellular Respiration or Fermentation?glucose2 pyruvate6 CO2 + 6 H2O2 ethanol + 2 CO2 or 2 lactateglycolysis2 ATPNo O2O2cellular respirationfermentation~25 ATPCellular Respiration or Fermentation?

Cellular respirationIf electron acceptor(such as oxygen)is presentIf electron acceptor(such as oxygen)is NOT present

Inefficient!Do not completely oxidize glucoseOnly utilize glycolysisOnly make 2 ATP per glucoseRegenerate NAD+

Do not produce enough energy to sustain large, active, multicelled organisms

Fermentation PathwaysFermentation PathwaysFirst step - GlycolysisGlucose 2 pyruvateGenerates 2 ATP and 2 NADH

Lactic Acid Fermentation2 Pyruvate 2 LactateRegenerates 2 NAD+

Alcoholic Fermentation2 Pyruvate 2 Ethanol (Ethyl Alcohol) + 2 CO2Regenerates 2 NAD+

No intermediate;pyruvate acceptselectrons from NADH2 Acetylaldehyde2 Pyruvate2 Pyruvate2 Lactate2 EthanolPyruvate ProcessingInputs:2 Pyruvate2 Coenzyme A2 NAD+

Outputs:2 Acetyl CoA2 NADH2 CO2

Location: mitochondiral matrixPyruvate ProcessingCoenzyme A enzyme cofactor that acts as acetyl group carrierwhen acetyl group has bound CoA, it is activated (easily transferred to acceptor molecule)

acetyl groupactivated

Coenzyme APyruvate ProcessingTracking Carbon and EnergyCarbon:Inputs:2 pyruvate (3-C each)Outputs:2 acetyl groups (carried by Coenzyme A) (2-C each)2 CO2

EnergyInputs:potential energy contained in bonds in pyruvateOutputs:potential energy in bonds in acetyl groups (carried by Coenzyme A)2 NADH (carry electrons/energy)Regulation of Pyruvate ProcessingPyruvate conversion to Acetyl CoA is catalyzed by the pyruvate dehydrogenase complex; key regulatory point in glucose oxidationInhibited by: (feedback inhibition)ATPAcetyl CoANADHActivated by:AMPCoANAD+

pyruvate dehydrogenase complexCitric Acid CycleCitrate is oxidized in a step-wise mannerElectrons (energy) transferred to NAD+ and FAD

Citric Acid CycleTracking Carbon and EnergyCarbon:Inputs:2 Acetyl groups (carried by Coenzyme A) (2-C each)Outputs:4 CO2

EnergyInputs:potential energy contained in bonds of acetyl groupsOutputs:2 ATP (substrate-level ATP synthesis)6 NADH (carry electrons/energy)2 FADH2 (carry electrons/energy)So Farsummary of steps 1-3Glucose has been fully oxidized to 6 CO2Potential energy released from glucose has been used to generate 4 ATP (substrate-level ATP synthesis) andElectrons (energy) released from glucose during oxidation have been used to reduce:2 FAD 2 FADH210 NAD+ 10 NADHGlucose(reduced)6 CO2(oxidized)NAD+ and FADH(oxidized)NADH and FADH2(reduced)This is were the energy is!Cellular Respiration: Overview

Electron Transport Chain and Chemiosmosis: SummaryElectrons (carried by NADH and FADH2) are delivered to the electron transport chain (ETC)Electrons are passed down the ETC to oxygen undergo redox reactions; release energyReleased energy is used to pump protons (H+) across inner mitochondrial membrane; generates a proton gradientEnergy in gradient (proton-motive force) is used to drive synthesis of ATP (via chemiosmosis) by ATP synthaseElectron Transport Chain - Overview

Membraneof cristaeComplexIIntermembranespaceComplexIIMitochondrialmatrixComplex IComplex IIComplex IIIComplex IVComplexIIIComplexIVThe electron transportchain occurs in theinner membrane of themitochondrion(membranes of cristae)Chemiosmosis- Overview

IntermembranespaceMitochondrialmatrixFo unitStatorRotorF1 unitElectron Transport ChainElectrons from NADH and FADH2 are passed down ETC to O2 (final electron acceptor); generates H+ gradient


ChemiosmosisProton (H+) electrochemical gradient drives ATP synthesis via ATP synthaseProton-Motive Force Energy associated with movement of H+ ions down their concentration gradient across the IMM Chemiosmosis production of ATP via a proton gradient

Cellular Respiration: Overview

GlycolysisPyruvate Processing and Citric Acid CycleGlucoseAcetyl CoAPyruvateOxaloacetateIn each of these drops,energy is transferred toenergy-storing moleculesATP, NADH, and FADH2

Series of chemical reactions, each catalyzed by a specific enzymeCellular respiration is a step-wise release of energy from glucoseDisruption of Chemiosmosis by PoisonsElectron Transport BlockersCyanideCO (carbon monoxide)UncouplerDNP (dinitrophenol)

Disruption of Chemiosmosis by PoisonsElectron Transport BlockersCyanideCO (carbon monoxide)UncouplerDNP (dinitrophenol)

Anaerobic RespirationWhat is the difference between anaerobic fermentation (previous slides) and anaerobic respiration?Anaerobic respiration involves the citric acid cycle and an electron transport chain, but this ETC uses a different final electron acceptor e.g. NO3- , SO42-, S, or Fe3+.Most species that perform anaerobic respiration are prokaryotes that live in environments devoid of O2.For more information, including the ecological and economic significance of these organisms, see Wikipedia: anaerobic respiration.Big Picture