Presentation on theme: "Cellular Respiration: Harvesting Chemical Energy"— Presentation transcript:
1 Cellular Respiration: Harvesting Chemical Energy Chapter 9Cellular Respiration: Harvesting Chemical Energy
2 Overview: Life Is Work Living cells Ex: The giant panda Require transfusions of energy from outside sources to perform their many tasksEx: The giant pandaObtains (chemical, potential) energy for its cells by eating plantsFigure 9.1
3 powers most cellular work EnergyFlows into an ecosystem as sunlight and leaves as heatLight energyECOSYSTEMCO2 + H2OPhotosynthesis in chloroplastsCellular respiration in mitochondriaOrganic molecules+ O2ATPpowers most cellular workHeat energyFigure 9.2
4 Review:1st law- Energy cannot be created or destroyed. Energy can be converted from one form to another. The sum of the energy before the conversion is equal to the sum of the energy after the conversion.2nd law- Some usable energy dissipates during transformations and is lost. During changes from one form of energy to another, some usable energy dissipates, usually as heat. The amount of usable energy therefore decreases.
5 Cellular Respiration Glucose + O2 energy (ATP) + CO2 + H2O This is exergonic –DG and converts one form of chemical energy (glucose) into another (ATP), with heat dissipatesConsumes oxygen and organic molecules (such as glucose)Glucose Oxidation is the most prevalent and efficient catabolic pathwayYields lots of ATPAn alternate catabolic process, fermentationIs a partial degradation of sugars that occurs without oxygen (in anaerobic conditions)
6 More on ATP ATP (adenosine triphosphate) ATP is a nucleotide. Nucleotides are the building blocks of nucleic acids such as DNA and RNA. They contain a nitrogen-containing base, a 5-carbon sugar, and phosphate groups.The energy in one glucose molecule is used to produce up to 38 ATP. ATP has approximately the right amount of energy for most cellular reactions.
7 ATP, ADP, AMPThe bonds between the phosphate groups are high-energy bonds. Energy is required (and stored) to form the bonds and energy is released when the bonds are broken. (below)
8 PhosphorylationATP is produced and used continuously. The entire amount of ATP in an organism is recycled once per minute. Most cells maintain only a few seconds supply of ATP.To keep working, cells must regenerate ATPWhen a phosphate group is transferred to another molecule, it is called PHOSPHORYLATION.ADP + Pi + energy ----> ATPIt takes about 7.3 kcals of energy to phosphorylate ADP into ATPEnzyme that catalyzes this reaction is ATP synthase
9 PhosphorylationPhosphate groups from ATP can also be transferred to other molecules.Enzymes that catalyze this reaction are called KINASES.In these phosphorylation reactions, energy is transferred from the phosphate group in ATP to the phosphorylated compound. This newly energized compound will participate in other reactions.
10 Redox Reactions: Oxidation and Reduction Catabolic pathways also yield energy due to the transfer of electronsIn oxidationA substance loses electrons, or is oxidizedIn reductionA substance gains electrons, or is reduced“Redox” reactionsTransfer electrons from one reactant to another by oxidation and reductionNa Cl Na Cl–becomes oxidized (loses electron)becomes reduced (gains electron)
11 “Redox” reactionsTransfer of electrons from one reactant to another by oxidation and reductionWhen the electron moves to a lower energy level, energy is released.
12 Redox cont’d Some redox reactions Do not completely exchange electrons, instead they change the degree of electron sharing in covalent bondsCH4HCOMethane (reducing agent)Oxygen (oxidizing agent)Carbon dioxideWater+2O2CO2Energy2 H2Obecomes oxidizedbecomes reducedReactantsProductsFigure 9.3
13 Oxidation of Organic Fuel Molecules During Cellular Respiration Glucose is oxidized and oxygen is reducedC6H12O6 + 6O CO2 + 6H2O + Energybecomes oxidizedbecomes reducedGlucose + Oxygen ----> Carbon dioxide + water + EnergyYields DG = -686 Kcal/moleThis energy is used to add phosphates to ADP + P ATPThere is a need to convert glucose (sugar) which is stored chemical energy into ATP which is usable cell energy
14 Electron carriersSome compounds can accept and donate electrons readily, and these are called electron carriers in organisms. There are a number of molecules that serve as electron carriers.NAD (nicotinamide adenine dinucleotide) is used in respiration. Reduced to NADH.NADP (nicotinamide adenine dinucleotide phosphate) is another used in photosynthesis. Reduced to NADPHThese molecules readily give up electrons (oxidized) and gain electrons (reduced).FAD (flavin adenine dinucleotide) is reduced to FADH2H often represents one electron, one proton.
15 The electron transport chain NADH, the reduced form of NAD+Passes the electrons along an electron transport chainElectron are passed in a series of steps instead of in one explosive reactionIf electron transfer is not stepwiseA large release of energy occurs = dangerous to living cellsUses the energy from the electron transfer to form ATP2 H1/2 O2(from food via NADH)2 H e–2 H+2 e–H2OControlled release of energy for synthesis of ATPATPElectron transport chainFree energy, G(b) Cellular respiration+Figure 9.5 B
16 ATP originates in cellular respiration What happens is that sugar is broken down into smaller molecules and energy is released.This energy is used to generate ATP from ADP and P.Sugar > smaller molecules >ADP + Pi > ATP
17 The Stages of Cellular Respiration: A Preview Respiration is a cumulative function of three metabolic stagesGlycolysisBreaks down glucose into two molecules of pyruvateThe citric acid (Krebs) cycleCompletes the breakdown of glucoseOxidative phosphorylationIs driven by the electron transport chain (ETC)Generates ATP
18 Oxidative phosphorylation: electron transport and chemiosmosis An overview of cellular respirationFigure 9.6Electronscarriedvia NADHGlycolsisGlucosePyruvateATPSubstrate-levelphosphorylationElectrons carriedvia NADH andFADH2Citric acid cycleOxidative phosphorylation: electron transport and chemiosmosisOxidativeMitochondrionCytosol
19 Both glycolysis and the citric acid cycle Can generate ATP by substrate-level phosphorylationFigure 9.7EnzymeATPADPProductSubstrateP+
20 Glycolysis Means “splitting of sugar” Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvateGlycolysisMeans “splitting of sugar”Breaks down glucose into pyruvateOccurs in the cytoplasm of the cell
21 Energy investment phase Glycolysis consists of two major phasesEnergy investment phaseEnergy payoff phaseGlycolysisCitric acid cycleOxidative phosphorylationATP2 ATP4 ATPusedformedGlucose2 ATP + 2P4 ADP + 42 NAD+ + 4 e- + 4 H +2 NADH+ 2 H+2 Pyruvate + 2 H2OEnergy investment phaseEnergy payoff phase4 ATP formed – 2 ATP used2 NAD+ + 4 e– + 4 H +Figure 9.8exergonic, energy liberating -DG endergonic, energy intake +DG
22 A closer look at the energy investment phase: [Step 1] Energy input required Terminal P from an ATP (-->ADP) is bonded to the C6 of a glucoseDG = (enzyme: hexokinase)[Step 2] glucose phosphate------> fructose-6-phosphateatoms rearrangedDG = (enzyme: phosphoglucoisomerase)[Step 3] fructose-6-phosphate------> fructose 1,6 biphosphatePhosphate added to C1DG = (enzyme: phosphofructokinase) splits into two products[Step 4] fructose -1, 6 - biphosphate---> dihydroxyacetone phosphateAND glyceraldehyde phosphate*DG = ( enzyme: aldolase)Our 6-carbon sugar is split into TWO 3-carbon products[Step 5] *Ultimately, all of the dihydroxyacetone phosphate will be converted into glyceraldehyde-3-phosphate, so each step is actually x 2 from here (because each of the two molecules will proceed through Steps 5- 9 )dihydroxyacetone phosphate > glyceraldehyde-3-phosphate(enzyme: isomerase)DihydroxyacetonephosphateGlyceraldehyde-3-phosphateHOHHOCH2OHOPCH2OCH2CCHOHATPADPHexokinaseGlucoseGlucose-6-phosphateFructose-6-phosphatePhosphoglucoisomerasePhosphofructokinaseFructose-1, 6-bisphosphateAldolaseIsomeraseGlycolysis12345OxidativephosphorylationCitricacidcycleFigure 9.9 A
23 A closer look at the energy payoff phase [Step 6] 2 Glyceraldehyde-3-phosphate molecules are then oxidized2 hydrogens (with e-) are removed, and NAD+ is reduced to NADH and H+Also, a free phosphate attaches to each of the glyceraldehyde-3-phosphates2 Glyceraldehyde-3-phosphate > 1, 3 biphosphoglycerate (x2)NAD+ is reduced to NADH and H+Pi = free phosphates, not taken from another molecule such as ATPNAD = nicotinamide adenine dinucleotide (niacin derivative)DG = (enzyme: triose phosphate dehydrogenase)[Step 7] a P is released from each 1,3 biphosphoglycerate molecule and is used to "recharge" 2 ADPs----> 2 ATPsthus, converting the 1,3 biphosphoglycerate to 3-phosphoglycerate(highly exergonic= large DG to pull preceding reactions forward)(x2) 1,3 Diphosphoglycerate > 3-phosphoglycerateADP---> ATPDG = (enzyme: phosphoglycerokinase)(x 2) [Step 8] The remaining P group is enzymatically transferred from the 3C tothe 2C3- phosphoglycerate > 2 - phosphoglycerateDG = (enzyme: phosphoglyceromutase)(x 2) [Step 9] A molecule of H2O removed2 - phosphoglycerate > phosphoenolpyruvate- H2ODG = (enzyme: enolase)(x 2) [Step 10] Another phosphate P is transferred to ADP( highly exergonic, pulls 2 preceding rxns!!!)phosphoenolpyruvate > pyruvate (pyruvic acid) DG = ( enzyme: pyruvate kinase)2 NAD+NADH2+ 2 H+Triose phosphatedehydrogenaseP iPCCHOHOCH2O–1, 3-Bisphosphoglycerate2 ADP2 ATPPhosphoglycerokinase3-PhosphoglyceratePhosphoglyceromutaseCH2OHH2-Phosphoglycerate2 H2OEnolasePhosphoenolpyruvatePyruvate kinaseCH3687910Pyruvate
24 Mitochondria ReviewThe mitochondrion is surrounded by two membranes. The outer is smooth and the inner folds inwards. The inner folds are called cristae. Within the inner compartment of the mitochondrion, surrounding the cristae, there is a dense solution known as the matrix. The matrix contains enzymes, co-enzymes, water, phosphates, and other molecules needed in respiration.The outer membrane is permeable to most small molecules, but the inner one permits the passage of only certain molecules, such as pyruvic acid and ATP.Proteins are built into the membrane of the cristae. These proteins are involved with the Electron Transport Chain. The inner membrane is about 80% protein and 20% lipids. 95% of the ATP generated by the heterotrophic cell is produced by the mitochondrion.
25 The Fate of the Pyruvate The pyruvate passes from the cytoplasm (where its produced thru glycolysis) and crosses the outer & inner membranes of the mitochondriaBefore entering the Krebs Cycle, the 3-C pyruvate molecule is oxidized: the carbon and oxygen atoms of the carboxyl group are removed (into CO2) and a 2-C acetyl group is left (CH3CO)In the course of this rxn, the carboxyl hydrogen reduces a molecule of NAD+ to NADHThe acetyl is momentarily accepted by a "coenzyme A" molecule (a large, complex molecule formed from pantothenic acid (vitamin B)), forming Acetyl-CoAFrom here the Acetyl CoA can enter the Krebs (aka, Citric Acid) Cycle. Acetyl CoA moves into the mitochondria and is completely dismantled by the enzymes in the mitochondria.
26 Before the citric acid cycle can begin Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysisCYTOSOLMITOCHONDRIONNADH+ H+NAD+231CO2Coenzyme APyruvateAcetyle CoASCoACCH3OTransport proteinO–Figure 9.10
27 An overview of the citric acid cycle Discovered 1937 by British biochemist Sir Hans Adolf KrebsCO2 is produced.Acetyls are dismantled and reconfigured. The electrons are what's important.The Krebs's cycle only gives us two molecules of ATP. Added with the two molecules of ATP made in Glycolysis, the total is now a meager four molecules of ATP.The remainder of the ATPs come from the Electron Transport System, which takes the electrons produced in the Krebs's cycle and makes ATP.ATP2 CO23 NAD+3 NADH+ 3 H+ADP + P iFADFADH2Citric acid cycleCoAAcetyle CoANADHCO2Pyruvate (from glycolysis, 2 molecules per glucose)GlycolysisOxidative phosphorylationFigure 9.11
28 A closer look at the citric acid cycle In general:2-C acetyl combines with 4-C oxaloacetic acid to form a 6-C citric acid.Two carbons (per cycle) are oxidized to CO2 which regenerates a molecule of oxaloacetic acidEach turn of the cycle uses up one acetyl group and regenerates a oxaloacetic acid, then begins the cycle again.Energy is released by breaking C-H and C-C bonds and is stored by transforming ADP to ATP (1 molecule per turn of the cycle) and to convert NAD+ to NADH and H+ (3x per cycle)Also, FAD (flavin adenine dinucleotide) is converted to FADH2 (one molecule per cycle)1. No oxygen is required in Krebs Cycle2. All e- and p+ are accepted by either NAD+ or FADThere are 8 steps in the cycle and the aim is to totally dismantle the Acetyl CoA, using only its electrons.We have totally taken apart the glucose molecule.Only four ATPs have resulted, 2 from glycolysis and 2 from the CAC.But we still have a lot of ELECTRONS captured in the form of NADH and FADH2 = potential energyAcetyl CoANADHOxaloacetateCitrateMalateFumarateSuccinateSuccinylCoAa-KetoglutarateIsocitrateCitricacidcycleSSHFADH2FADGTPGDPNAD+ADPP iCO2H2O+ H+CCH3OCOO–CH2HOHCCH12345678GlycolysisOxidativephosphorylationATPFigure 9.12Figure 9.12
29 Oxidative phosphorylation Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesisNADH and FADH2Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
30 The Pathway of Electron Transport In the electron transport chainElectrons from NADH and FADH2 lose energy in several stepsAt the end of the chainElectrons are passed to oxygen, forming waterTransport Chain carriers are called CYTOCHROMES (consist of protein and a heme group = atom of iron enclosed in a porphyrin ring (note the similarity to hemoglobin!)electrons are "passed down" a "staircase" of cytochromes and the energy released in lowering the energy level is stored in additional ATP molecules...called Oxidative Phosphorylationremember, the energy from lowering electrons can do this: ADP + P = ATP---> for every e- passed down the chain from NADH, 3 ATPs are formed---> for every 2e- from FADH2, 2 ATP's are formedH2OO2NADHFADH2FMNFe•SOFADCyt bCyt c1Cyt cCyt aCyt a32 H + + 12IIIIIIIVMultiprotein complexes1020304050Free energy (G) relative to O2 (kcl/mol)Figure 9.13
31 Chemiosmosis: The Energy-Coupling Mechanism ATP synthaseIs the enzyme that actually makes ATPINTERMEMBRANE SPACEH+P i+ADPATPA rotor within the membrane spins clockwise when H+ flows past it down the H+ gradient.A stator anchored in the membrane holds the knob stationary.A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob.Three catalytic sites in the stationary knob join inorganicPhosphate to ADP to make ATP.MITOCHONDRIAL MATRIXFigure 9.14
32 ChemiosmosisIs an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular workAt certain steps along the electron transport chain, electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane spaceThe resulting H+ gradientStores energyDrives chemiosmosis in ATP synthaseIs referred to as a “proton-motive force”
33 Electron transport chain Oxidative phosphorylation Chemiosmosis and the electron transport chainOxidativephosphorylation.electron transportand chemiosmosisGlycolysisATPInnerMitochondrialmembraneH+P iProtein complexof electroncarnersCyt cIIIIIIIV(Carrying electronsfrom, food)NADH+FADH2NAD+FAD+2 H+ + 1/2 O2H2OADP +Electron transport chainElectron transport and pumping of protons (H+),which create an H+ gradient across the membraneChemiosmosisATP synthesis powered by the flowOf H+ back across the membranesynthaseQOxidative phosphorylationIntermembranespacemitochondrialmatrixFigure 9.15
34 There are three main processes in this metabolic enterprise SummaryThere are three main processes in this metabolic enterpriseElectron shuttlesspan membraneCYTOSOL2 NADH2 FADH26 NADHGlycolysisGlucose2PyruvateAcetylCoACitricacidcycleOxidativephosphorylation:electron transportandchemiosmosisMITOCHONDRIONby substrate-levelphosphorylationby oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosolMaximum per glucose:About36 or 38 ATP+ 2 ATP+ about 32 or 34 ATPorFigure 9.16
35 The energy tally sheet Glycolysis: 2 ATP =2 ATP 2 NADH ets 6 ATP =6 ATPOxidation: pyruvate acetyl CoA 1 NADH ets 3 ATP (x2) = 6 ATPCAC/Krebs 1 ATP x2 turns 2 ATP3 NADH ets 9 ATP x2 turns 18 ATP1 FADH2 ets 2 ATP x2 turns 4 ATP = 24 ATPTOTAL = 38 ATP
36 efficiencyLess than 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making approximately 38 ATPDG =ADP + Pi --> ATP= about 7 kcal/moleX 38 = 266 kcal/mole (captured in P bonds)DG = -686 kcal/mole (free energy change during glycolysis and oxidation for glucose)= about 39% efficiency
37 Oxidative cellular respiration FERMENTATIONConcept 9.5: Fermentation enables some cells to produce ATP without the use of oxygenOxidative cellular respirationRelies on oxygen to produce ATPInvolves Krebs cycle and ETSIn the absence of oxygenCells can still produce a little bit of ATP through fermentation
38 Without oxygen: Glycolysis Can produce ATP with or without oxygen, in either aerobic or anaerobic conditionsPyruvate is produced, some ATP is madeIn anaerobic respiration (fermentation) pyruvate must be processed in the absence of oxygenThe breakdown of the sugar still takes place through a series of chemical reactions, but with a different outcome.
39 The Evolutionary Significance of Glycolysis Occurs in the cytoplasm of nearly all organismsProbably evolved in ancient prokaryotes before there was oxygen in the atmosphere
40 Pyruvate is a key juncture in catabolism GlucoseCYTOSOLPyruvateNo O2 presentFermentationO2 presentCellular respirationEthanolorlactateAcetyl CoAMITOCHONDRIONCitricacidcycleFigure 9.18
41 FermentationLiving organisms have developed numerous and different fermentation pathways; however, most organisms use the following Embden-Meyerhoff pathway, named for the two discoverers.The pyruvate can take two pathways in anaerobic respiration:a. Pyruvate will be converted to ethyl alcohol (ethanol) and carbon dioxide. This is called alcoholic fermentation and is the basis of our wine, beer and liquor industry.b. The pyruvate will be converted to lactic acid. This is called lactic acid fermentation. Lactic acid is what makes your muscles burn during prolonged exercise, this process is also used to make yogurt.
42 Fermentation consists of Types of FermentationFermentation consists ofGlycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysisIn alcohol fermentationPyruvate is converted to ethanol in two steps, one of which releases CO2During lactic acid fermentationPyruvate is reduced directly to NADH to form lactate as a waste product
44 Fermentation and Cellular Respiration Compared Both fermentation and cellular respirationUse glycolysis to oxidize glucose and other organic fuels to pyruvateFermentation and cellular respirationDiffer in their final electron acceptorOxidative cellular respirationProduces more ATP
45 The Versatility of Catabolism Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathwaysCatabolic pathwaysFunnel electrons from many kinds of organic molecules into cellular respiration
46 The catabolism of various molecules from food AminoacidsSugarsGlycerolFattyGlycolysisGlucoseGlyceraldehyde-3- PPyruvateAcetyl CoANH3CitricacidcycleOxidativephosphorylationFatsProteinsCarbohydratesFigure 9.19
47 Regulation of Cellular Respiration via Feedback Mechanisms Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycleEnzyme 1Enzyme 2Enzyme 3ABCDReaction 1Reaction 2Reaction 3Starting moleculeProduct
48 Feedback Control Regulates Biological Processes The control of cellular respirationGlucoseGlycolysisFructose-6-phosphatePhosphofructokinaseFructose-1,6-bisphosphateInhibitsPyruvateATPAcetyl CoACitricacidcycleCitrateOxidativephosphorylationStimulatesAMP+–Figure 9.20