How Cells Release Stored Energy – Cellular Respiration

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How Cells Release Stored Energy Cellular Respiration. Aerobic Respiration: Whole Organism. Aerobic respiration at the whole organism level = process by which gases are exchanged with the environment. O 2. CO 2. Aerobic Respiration: Whole Organism. - PowerPoint PPT Presentation


  • How Cells Release Stored Energy Cellular Respiration

  • Aerobic Respiration: Whole OrganismAerobic respiration at the whole organism level = process by which gases are exchanged with the environment. O2 CO2

  • Aerobic Respiration: Whole OrganismRespiratory Surface (= part of the organism where O2 diffuses into and CO2 diffuses out of the organism) must be moist, as gases must be dissolved in water before they can diffuse in or out.

  • Aerobic Respiration: Whole OrganismIn unicellular aquatic protozoans: O2 dissolved in water passes across the cell membrane by diffusion, and CO2 exits.O2 CO2

  • Aerobic Respiration: Whole OrganismIn multicellular aquatic plants and invertebrate animals: O2 dissolved in water enters cells by diffusion, and CO2 exits by diffusion.Elodea cellO2CO2Planarian

  • Aerobic Respiration: Whole OrganismIn insects: O2 enters through small openings in the body wall (spiracles) and is carried through tracheal tubes to moist cell membranes, across which respiratory exchange occurs. spiracleSpiraclesSEM

  • Aerobic Respiration: Whole OrganismIn fish: O2 (in H2O) diffuses across the surface of gills, into capillaries of the circulatory system and CO2 diffuses in the opposite direction.

  • Cellular Respiration:THE BIG PICTURECellular respiration is the process by which organisms can get energy (ATP) from their food (glucose)Cellular respiration is CRITICAL for lifeOccurs in BOTH plants and animalsTwo main mechanismsAerobic cellular Respiration Requires OxygenAnaerobic cellular Respiration Does not require Oxygen

  • Main Types of Cellular Respiration Pathways Aerobic Respiration

    Evolved laterRequire oxygenStart with glycolysis in cytoplasmCompleted in mitochondriaAnaerobic Respiration

    Evolved firstDont require oxygenStart with glycolysis in cytoplasmCompleted in cytoplasm

  • Aerobic RespirationOverall Equation:

    C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water dioxideSeveral steps occur in the middle (intermediates)Each step (rxn) catalyzed by enzymes

  • Aerobic respiration OverviewStage One:Glycolysis (cytoplasm)Stage Two:Preparation for Krebs (mitochondrial matrix)Krebs Cycle (matrix)Stage Three:Electron Transfer Chain (across inner membrane of mitochondria)

  • The Role of Carrier MoleculesSeveral oxidation-reduction rxns take place in aerobic respiration (Glucose gets oxidized to carbon dioxide)In order to aid in the redox rxns, enzymes use carrier molecules NAD+ and FAD to carry electrons from broken down glucose to the electron transfer chainNAD+ and FAD accept electrons and hydrogen to become NADH and FADH2 during the first two stages of aerobic respiration (Glycolysis, Krebs) and deliver electrons and hydrogen to the Electron Transfer Chain to make ATP

  • Stage One: GlycolysisGlucose (6-carbon) is broken down into 2 molecules of pyruvate (3-carbon)Yields 2 ATP by substrate level phosphorylation

  • 2 NADH2 NADHGlycolysis: Overall ReactionGlucose(6C)2 ATP2 ADPFructoseBisphosphate(6C)G3P(3C)G3P(3C)Pyruvate(3C)Pyruvate(3C)2 ADP2 ATP2 ADP2 ATP2 NAD+2 NAD+

  • Aerobic Respiration:1. Glycolysis

  • Glycolysis: Net Yield Energy requiring steps: 2 ATP invested

    Energy releasing steps:2 NADH formed 4 ATP formed

    Net yield: 2 ATP + 2 NADH + 2 molecules of Pyruvic Acid

  • What happens next?Depends on the organism and the presence of oxygenIf oxygen is around: Aerobic respiration, proceed to Krebs cycleIf no oxygen: Anaerobic respiration, Proceed to Fermentation

  • Second Stage: Krebs cyclePreparatory reactions: Oxidation of pyruvatePyruvic acid is oxidized into two-carbon acetyl CoA units and carbon dioxideNAD+ is reduced into NADH2Krebs cycleThe acetyl units are oxidized to carbon dioxideNAD+ and FAD are reduced into FADH and NAHD2

  • Oxidation of Pyruvate

  • The Krebs CycleOverall Products

    Coenzyme A2 CO23 NADHFADH2ATPOverall Reactants

    Acetyl-CoA3 NAD+FADADP and Pi

  • Results of the Second StageAll of the carbon atoms in pyruvate end up in carbon dioxideNAD and FAD are reduced (they pick up electrons and hydrogen)One molecule of ATP forms Four-carbon oxaloacetate regenerates

  • NAD/FAD Reductions during First Two Stages

    Glycolysis2 NADH2Preparatoryreactions 2 NADH2Krebs cycle 2 FADH2 + 6 NADH2

    Total 2 FADH2 + 10 NADH2

  • Occurs in the mitochondriaCoenzymes deliver electrons to electron transfer chainsElectron transfer sets up H+ ion gradientsFlow of H+ down gradients powers ATP formationElectron Transfer Chain

  • Importance of OxygenOxygen is the finial Electron acceptor

    Electron transport chain requires the presence of oxygen

    Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water

  • Summary of Energy Harvest(per molecule of glucose)Glycolysis2 ATP formed byKrebs cycle and preparatory reactions2 ATP formedElectron transport chain32 ATP formed

  • 686 kcal of energy are released 7.5 kcal are conserved in each ATPWhen 36 ATP form, 270 kcal (36 X 7.5) are captured in ATPEfficiency is 270 / 686 X 100 = 39 percent Most energy is lost as HEAT!Efficiency of Aerobic Respiration

  • Do not use oxygenProduce less ATP than aerobic pathwaysAnaerobic Pathways

  • Fermentation PathwaysBegin with glycolysisDo not break glucose down completely to carbon dioxide and waterYield only the 2 ATP from glycolysisSteps that follow glycolysis serve only to regenerate NAD+

  • When life originated, atmosphere had little oxygenEarliest organisms used anaerobic pathwaysLater, noncyclic pathway of photosynthesis increased atmospheric oxygenCells arose that used oxygen as final acceptor in electron transportEvolution of Metabolic Pathways

  • Summary of Cellular Respiration

    Respiration ProcessWhere Process OccursNet Gain of ATPPer GlucoseAnaerobic Glycolysis & FermentationCytoplasm2 ATPAerobic Krebs Cycle and Electron TransportMitochondrion36 ATP

  • ATP / ADP CycleATP is constantly being used and remade in the cell.Energy is released or stored by breaking or making a phosphate bond.



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