Overview: Life Is WorkSlide 2Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels and use it to make ATPRedox Reactions: Oxidation and ReductionRedox Reaction: Oxidation and ReductionOxidation of Organic Fuel Molecules During Cellular RespirationStepwise Energy Harvest via NAD+ and the Electron Transport ChainSlide 8The Stages of Cellular Respiration: A PreviewSlide 10During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesisSlide 12Slide 13Fermentation enable cells to produce ATP without the use of oxygenSlide 15Overview: Life Is Work•Living cells require energy from outside sources•Some animals, obtain energy by eating plants, and some animals feed on other organisms that eat plants•Energy flows into an ecosystem as sunlight and leaves as heat•Photosynthesis generates O2 and organic molecules, which are used in cellular respiration(aerobic) •Cells use chemical energy stored in organic molecules to regenerate ATP, which powers workFig. 9-2LightenergyECOSYSTEMPhotosynthesis in chloroplastsCO2 + H2OCellular respirationin mitochondriaOrganicmolecules+ O2ATP powers most cellular workHeatenergyATPConcept 9.1: Catabolic pathways yield energy by oxidizing organic fuels and use it to make ATP•Fermentation is a partial degradation of sugars that occurs without O2•Aerobic respiration consumes organic molecules and O2 and yields ATP•Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)Redox Reactions: Oxidation and Reduction•The transfer of electrons during chemical reactions releases energy stored in organic molecules•This released energy is ultimately used to synthesize ATP•Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions•In oxidation, a substance loses electrons, or is oxidized•In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)Fig. 9-UN1becomes oxidized(loses electron)becomes reduced(gains electron)Redox Reaction: Oxidation and ReductionFig. 9-UN3becomes oxidizedbecomes reducedOxidation of Organic Fuel Molecules During Cellular Respiration•During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced:Stepwise Energy Harvest via NAD+ and the Electron Transport Chain•In cellular respiration, glucose and other organic molecules are broken down in a series of steps•Oxidation of glucose is carried out by certain enzymes. These enzymes need the help of coenzymes like, NAD+ and FAD•Electrons from organic compounds are usually first transferred to NAD+, a coenzyme•As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration, and converts from NA D+ to NADH after accepting electrons•Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP•NADH then passes the electrons to the electron transport chain•O2 pulls electrons down the chain in an energy-yielding tumble•The energy yielded is used to regenerate ATPThe Stages of Cellular Respiration: A Preview•Cellular respiration has three stages:1. Glycolysis (breaks down glucose into two molecules of pyruvate, ocurs in Cytoplasm, Glycolysis can take place both in presence and absence of Oxygen)2. The citric acid cycle (completes the breakdown of glucose, only in presence of oxygen, occurs in mitochondrial matrix)3. Oxidative phosphorylation (accounts for most of the ATP synthesis, occurs in inner mitochondrial memebrane)Fig. 9-6-3MitochondrionSubstrate-levelphosphorylationATPCytosolGlucosePyruvateGlycolysisElectronscarried via NADHSubstrate-levelphosphorylationATPElectrons carriedvia NADH andFADH2OxidativephosphorylationATPCitricacidcycleOxidativephosphorylation:electron transportandchemiosmosisDuring oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis•Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food•These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation•Oxidative phosphorylation Consists of •1. Electron transport chain•2. ChemiosmosisFig. 9-16Protein complexof electroncarriersH+H+H+Cyt cQVFADH2FADNAD+NADH(carrying electronsfrom food)Electron transport chain2 H+ + 1/2O2H2OADP +PiChemiosmosisOxidative phosphorylationH+H+ATP synthaseATP21Fig. 9-17Maximum per glucose:About36 or 38 ATP+ 2 ATP+ 2 ATP + about 32 or 34 ATPOxidativephosphorylation:electron transportandchemiosmosisCitricacidcycle2AcetylCoAGlycolysisGlucose2Pyruvate2 NADH2 NADH6 NADH 2 FADH22 FADH22 NADHCYTOSOLElectron shuttlesspan membraneorMITOCHONDRIONFermentation enable cells to produce ATP without the use of oxygen•In the absence of O2, fermentation undergoes Glycolysis alone(which is the the 1st stage) to produces ATP•Two common types are alcohol fermentation and lactic acid fermentation•Alcohol fermentation by yeast is used in brewing, winemaking, and baking•Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt•Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarceFig. 9-19GlucoseGlycolysisPyruvateCYTOSOLNo O2 present:FermentationO2 present: Aerobic cellular respirationMITOCHONDRIONAcetyl