How Cells Release Stored Energy Cell respiration

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  • How Cells Release Stored EnergyCell respiration

  • When a molecule has hydrogen, it has more energy and removing them releases the energy. The energy produced from the "burning" of glucose is used to make ATP. In chemistry this process is called the oxidation of glucose. The hydrogen carriers NAD and FAD are used to help release the energy in glucose by moving hydrogens and electrons around.

  • A simple sugar(C6H12O6)

    Atoms held together by covalent bondsGlucose In-text figure Page 136

  • Summary Equation for Aerobic Respiration

    C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water dioxide

  • Glycolysis -in cytoplasm-does not use oxygenOccurs in Two Stages Energy-requiring steps ATP energy activates glucose and its six-carbon derivativesActually uses 2 ATPsEnergy-releasing stepsThe products of the first part are split into 2 three carbon pyruvate molecules4 ATP and 2NADH form4 ATPs form 2 ATPs used = 2 net ATPs made

  • Glycolysis is often called anaerobic respriation because it does not need oxygen. This process occurs in the cytoplasm. Two net molecules of ATP are made for cell use. It involves glucose being converted to two molecules of pyruvic acid (or pyruvate).

    This process is not very efficient at converting the energy of glucose into ATP as only 2 ADP are phosphorylated instead of 32 as in Krebs and chemiosmosis.

  • Energy-Requiring Steps Figure 8.4(2) Page 137

  • Energy-Releasing StepsADPpyruvateADPpyruvateH2OPEPH2OPEP2-phosphoglycerate2-phosphoglycerateADP3-phosphoglycerateADP3-phosphoglycerateNAD+NADHPi1,3-bisphosphoglycerateNAD+NADHPi1,3-bisphosphoglyceratePGALPGALFigure 8.4 Page 137Phosphorylations

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

    Energy releasing steps:2 NADH formed 4 ATP formed

    Net yield is 2 ATP, 2 pyruvic acid and 2 NADH

  • After glycolysis:-If oxygen is present, the pyruvic acid will go into the mitochondria where the Krebs cycle (or citric acid cycle) is performed followed by the ETC. This allows the rest of the energy stored in the hydrogen to be extracted. -If no there is no oxygen, then the Kreb's cycle can not be completed (or started in some organisms). A cell can continue doing glycolysis in the absence of oxygen to produce some ATP, BUT it must regenerate NAD to keep glycolysis going. This is called anaerobic respiration (or fermentation). Pyruvate will form either lactic acid (muscles) or ethanol (bacteria, yeast or plants). In either case NAD is regenerated so that glycolysis can continue.

  • 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+

  • Lactate FermentationC6H12O6ATPATPNADH2 lactateelectrons, hydrogen from NADH2 NAD+22 ADP2 pyruvate24energy outputenergy inputGLYCOLYSISLACTATE FORMATION2 ATP net

  • Alcoholic FermentationC6H12O6ATPATPNADH2 acetaldehydeelectrons, hydrogen from NADH2 NAD+22 ADP2 pyruvate24energy outputenergy inputGLYCOLYSISETHANOL FORMATION2 ATP net2 ethanol2 H2O2 CO2

  • Anaerobic Electron TransportCarried out by certain bacteriaElectron transfer chain is in bacterial plasma membrane Final electron acceptor is compound from environment (such as nitrate), not oxygenATP yield is low

  • After glysolysis, if oxygen is present aerobic respiration proceeds in the mitochondria.

  • Preparatory reactionsPyruvate is decarboxylated and oxidized (releasing carbon dioxide)NAD+ is reducedAcetyl Co-A is formedEx. 1PreparatoryStepsEx. 2

  • The Krebs CycleOverall Products

    Coenzyme A2 CO23 NADHFADH2ATPOverall Reactants

    Acetyl-CoA3 NAD+FADADP and Pi

  • The enzymes for Kreb's is found in the inner compartment of the mitochondria. Summary of Krebs- Occurs in Mitochondria 2X'sPyruvate---> 3 CO2 6 CO2 1 ADP ---> 1 ATP 2 ATP4 NAD ---> 4 NADH 8 NADH1 FAD ---> 1 FADH2 2 FADH2(also, oxaloacetate regenerates so cycle can continue)

  • Coenzyme Reductions during First Two Stages

    Glycolysis2 NADHPreparatoryreactions 2 NADHKrebs cycle 2 FADH2 + 6 NADH

    Total 2 FADH2 + 10 NADH

  • Occurs in the mitochondriaCoenzymes deliver electrons to electron transfer chainsElectron transfer sets up H+ ion gradientsFlow of H+ down gradients powers ATP formation (chemiosmotic)Electron Transfer Phosphorylation

  • The purpose of chemiosmosis is to extract the energy found in NADH and FADH2 to make more ATP. This involves the cristae. There are electron transport chains that are used.The electrons from the NADH and FADH2 are used to move on the electron transport chain. As the electrons move down the electron transport chain, H+ ions are pumped across the membrane.The electrons from one NADH can pump 6 H+ across the membrane, but the electrons from FADH2 can only pump 4 H+ across the membrane.


  • The outer compartment of the mitochondria becomes positive and the inside becomes negative like a battery. This "battery" can do work. The hydrogen ions can cross an F1 particle and make ATP.It takes 2 H+ to cross the F1 particle to provide enough energy to make ATP.

  • Making ATP: Chemiosmotic ModelATPADP + PiINNER COMPARTMENT

  • Summary8 NADH2 x 6 H = 48 H+2 FADH2(Krebs)x 4 H = 8 H+2 FADH2(glyc.) X 4 H = 8 H+ 64 H+

    64 H+ --> 32 ATP

  • Importance of OxygenElectron transport phosphorylation 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 by substrate-level phosphorylationKrebs cycle and preparatory reactions2 ATP formed by substrate-level phosphorylationElectron transport phosphorylation32 ATP formed

  • Overview of Aerobic RespirationCYTOPLASMGlycolysisElectron Transfer PhosphorylationKrebsCycleATPATP2 CO24 CO2232water2 NADH8 NADH2 FADH22 NADH2 pyruvatee- + H+e- + oxygen(2 ATP net)glucoseTypical Energy Yield: 36 ATPe-e- + H+e- + H+ATPH+e- + H+ATP24Figure 8.3 Page 135

  • 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 (at best)Most energy is lost as heatEfficiency of Aerobic Respiration

  • **Fats/Lipids = Glycerol and 3 fatty acidsGlycerol is converted to PGAL and respired in glycolysis. The fatty acids are chopped into 2 carbon acetyl groups and used in the Krebs or citric acid cycle. **Proteins = amino acidsThe amino acids are sent to the liver where the liver removes the amine group. The left over acid is then used at some point in the Krebs cycle.

  • Alternative Energy SourcesFOODcomplex carbohydratessimple sugars

    pyruvateacetyl-CoAglycogenfatsproteinsamino acidscarbon backbonesfatty acidsglycerolNH3PGALglucose-6-phosphateGLYCOLYSISKREBS CYCLEureaFigure 8.11 Page 145Other organic molecules can be involved in respiration.

  • When life originated, atmosphere had little (none) free oxygenEarliest organisms used anaerobic pathwaysLater, noncyclic pathway of photosynthesis increased atmospheric oxygenCells arose that used oxygen as final acceptor in electron transport and were more efficient Evolution of Metabolic Pathways

  • Processes Are Linked sunlight energywater+carbon dioxidePHOTOSYNTHESISAEROBIC RESPIRATIONsugar moleculesoxygenIn-text figure Page 146

  • Linked ProcessesPhotosynthesis

    Energy-storing pathway

    Releases oxygen

    Requires carbon dioxide

    Makes carbsAerobic Respiration

    Energy-releasing pathway

    Requires oxygen

    Releases carbon dioxide

    Breaks carbs



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