Sinh học - Chapter 6: How cells harvest chemical energy

Chapter 6How Cells Harvest Chemical Energy0IntroductionIn eukaryotes, cellular respirationharvests energy from food,yields large amounts of ATP, andUses ATP to drive cellular work.A similar process takes place in many prokaryotic organisms.© 2012 Pearson Education, Inc.Figure 6.0_1Chapter 6: Big IdeasCellular Respiration:Aerobic Harvestingof EnergyStages of CellularRespirationFermentation: AnaerobicHarvesting of EnergyConnections BetweenMetabolic Pathways CELLULAR RESPIRATION: AEROBIC HARVESTING OF ENERGY © 2012 Pearson Education, Inc.6.1 Photosynthesis and cellular respiration provide energy for lifeLife requires energy.In almost all ecosystems, energy ultimately comes from the sun.In photosynthesis,some of the energy in sunlight is captured by chloroplasts,atoms of carbon dioxide and water are rearranged, andglucose and oxygen are produced.© 2012 Pearson Education, Inc.6.1 Photosynthesis and cellular respiration provide energy for lifeIn cellular respirationglucose is broken down to carbon dioxide and water andthe cell captures some of the released energy to make ATP.Cellular respiration takes place in the mitochondria of eukaryotic cells.© 2012 Pearson Education, Inc.Figure 6.1Sunlight energyECOSYSTEMPhotosynthesisin chloroplastsCellular respirationin mitochondria(for cellularwork)Heat energyGlucoseCO2H2OO2ATPFigure 6.1_1Sunlight energyECOSYSTEMPhotosynthesisin chloroplastsCellular respirationin mitochondria(for cellularwork)Heat energyGlucoseCO2H2OO2ATP6.2 Breathing supplies O2 for use in cellular respiration and removes CO2Respiration, as it relates to breathing, and cellular respiration are not the same.Respiration, in the breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from the environment and releases waste CO2.Cellular respiration is the aerobic (oxygen requiring) harvesting of energy from food molecules by cells.© 2012 Pearson Education, Inc.Figure 6.2BreathingLungsBloodstreamCO2O2O2CO2Muscle cells carrying outCellular RespirationGlucose  O2CO2  H2O  ATP6.3 Cellular respiration banks energy in ATP moleculesCellular respiration is an exergonic process that transfers energy from the bonds in glucose to form ATP.Cellular respirationproduces up to 32 ATP molecules from each glucose molecule andcaptures only about 34% of the energy originally stored in glucose.Other foods (organic molecules) can also be used as a source of energy.© 2012 Pearson Education, Inc.Figure 6.3GlucoseOxygenWaterCarbondioxideC6H12O6O2H2OATP666 HeatCO26.4 CONNECTION: The human body uses energy from ATP for all its activitiesThe average adult human needs about 2,200 kcal of energy per day.About 75% of these calories are used to maintain a healthy body.The remaining 25% is used to power physical activities.© 2012 Pearson Education, Inc.6.4 CONNECTION: The human body uses energy from ATP for all its activitiesA kilocalorie (kcal) isthe quantity of heat required to raise the temperature of 1 kilogram (kg) of water by 1oC,the same as a food Calorie, andused to measure the nutritional values indicated on food labels. © 2012 Pearson Education, Inc.Figure 6.4Activitykcal consumed per hourby a 67.5-kg (150-lb) person*Running (8–9 mph)Dancing (fast)Bicycling (10 mph)Swimming (2 mph)Walking (4 mph)Walking (3 mph)Dancing (slow)Driving a carSitting (writing)*Not including kcal needed forbody maintenance97951049040834124520461286.5 Cells tap energy from electrons “falling” from organic fuels to oxygenThe energy necessary for life is contained in the arrangement of electrons in chemical bonds in organic molecules.An important question is how do cells extract this energy?© 2012 Pearson Education, Inc.6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenWhen the carbon-hydrogen bonds of glucose are broken, electrons are transferred to oxygen.Oxygen has a strong tendency to attract electrons.An electron loses potential energy when it “falls” to oxygen.© 2012 Pearson Education, Inc.6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenEnergy can be released from glucose by simply burning it.The energy is dissipated as heat and light and is not available to living organisms.© 2012 Pearson Education, Inc.6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenOn the other hand, cellular respiration is the controlled breakdown of organic molecules.Energy isgradually released in small amounts, captured by a biological system, andstored in ATP.© 2012 Pearson Education, Inc.6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenThe movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction. In a redox reaction,the loss of electrons from one substance is called oxidation,the addition of electrons to another substance is called reduction,a molecule is oxidized when it loses one or more electrons, andreduced when it gains one or more electrons.© 2012 Pearson Education, Inc.6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenA cellular respiration equation is helpful to show the changes in hydrogen atom distribution.Glucoseloses its hydrogen atoms andbecomes oxidized to CO2.Oxygengains hydrogen atoms andbecomes reduced to H2O.© 2012 Pearson Education, Inc.Figure 6.5AGlucose HeatC6H12O6O2CO2H2OATP666Loss of hydrogen atoms(becomes oxidized)Gain of hydrogen atoms(becomes reduced)6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenEnzymes are necessary to oxidize glucose and other foods.NAD+is an important enzyme in oxidizing glucose,accepts electrons, andbecomes reduced to NADH.© 2012 Pearson Education, Inc.Figure 6.5BBecomes oxidizedBecomes reduced2H2HNADNADHHH22(carries2 electrons)6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenThere are other electron “carrier” molecules that function like NAD+.They form a staircase where the electrons pass from one to the next down the staircase.These electron carriers collectively are called the electron transport chain.As electrons are transported down the chain, ATP is generated.© 2012 Pearson Education, Inc.Figure 6.5CControlledrelease ofenergy forsynthesisof ATPNADHNADHHO2H2O222ATPElectron transport chain21STAGES OF CELLULAR RESPIRATION© 2012 Pearson Education, Inc.6.6 Overview: Cellular respiration occurs in three main stagesCellular respiration consists of a sequence of steps that can be divided into three stages.Stage 1 – GlycolysisStage 2 – Pyruvate oxidation and citric acid cycleStage 3 – Oxidative phosphorylation© 2012 Pearson Education, Inc.6.6 Overview: Cellular respiration occurs in three main stagesStage 1: Glycolysisoccurs in the cytoplasm,begins cellular respiration, andbreaks down glucose into two molecules of a three-carbon compound called pyruvate.© 2012 Pearson Education, Inc.6.6 Overview: Cellular respiration occurs in three main stagesStage 2: The citric acid cycletakes place in mitochondria,oxidizes pyruvate to a two-carbon compound, and supplies the third stage with electrons.© 2012 Pearson Education, Inc.6.6 Overview: Cellular respiration occurs in three main stagesStage 3: Oxidative phosphorylationinvolves electrons carried by NADH and FADH2,shuttles these electrons to the electron transport chain embedded in the inner mitochondrial membrane,involves chemiosmosis, andgenerates ATP through oxidative phosphorylation associated with chemiosmosis.© 2012 Pearson Education, Inc.Figure 6.6NADHNADHFADH2ATPATPATPCYTOPLASMGlycolysisElectronscarried by NADHGlucosePyruvatePyruvateOxidationCitric AcidCycleOxidativePhosphorylation(electron transportand chemiosmosis)MitochondrionSubstrate-levelphosphorylationSubstrate-levelphosphorylationOxidativephosphorylationFigure 6.6_1NADHNADHFADH2ATPATPATPCYTOPLASMGlycolysisElectronscarried by NADHGlucosePyruvatePyruvateOxidationCitric AcidCycleOxidativePhosphorylation(electron transportand chemiosmosis)MitochondrionSubstrate-levelphosphorylationSubstrate-levelphosphorylationOxidativephosphorylation6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvateIn glycolysis,a single molecule of glucose is enzymatically cut in half through a series of steps,two molecules of pyruvate are produced,two molecules of NAD+ are reduced to two molecules of NADH, anda net of two molecules of ATP is produced.© 2012 Pearson Education, Inc.Figure 6.7AGlucose2 Pyruvate2 ADP2 P2 NAD2 NADH2 HATP26.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvateATP is formed in glycolysis by substrate-level phosphorylation during whichan enzyme transfers a phosphate group from a substrate molecule to ADP andATP is formed.The compounds that form between the initial reactant, glucose, and the final product, pyruvate, are called intermediates.© 2012 Pearson Education, Inc.Figure 6.7BEnzymeEnzymePPADPPATPSubstrateProduct6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvateThe steps of glycolysis can be grouped into two main phases.In steps 1–4, the energy investment phase, energy is consumed as two ATP molecules are used to energize a glucose molecule, which is then split into two small sugars that are now primed to release energy.In steps 5–9, the energy payoff,two NADH molecules are produced for each initial glucose molecule and ATP molecules are generated.© 2012 Pearson Education, Inc.Figure 6.7Ca_s1GlucoseGlucose 6-phosphateFructose 6-phosphateFructose 1,6-bisphosphateENERGYINVESTMENTPHASEPPPPADPADPATPATPStepSteps – A fuelmolecule is energized,using ATP.33211Figure 6.7Ca_s2GlucoseGlucose 6-phosphateFructose 6-phosphateFructose 1,6-bisphosphateGlyceraldehyde3-phosphate (G3P)ENERGYINVESTMENTPHASEPPPPPPADPADPATPATPStepSteps – A fuelmolecule is energized,using ATP.Step A six-carbonintermediate splitsinto two three-carbonintermediates.4433211Figure 6.7Cb_s1555Step A redox reactiongenerates NADH.ENERGYPAYOFFPHASE1,3-Bisphospho-glycerateNADHNADHNADNADHHPPPPPPPPFigure 6.7Cb_s26665559998877Step A redox reactiongenerates NADH.Steps – ATP and pyruvateare produced.ENERGYPAYOFFPHASE1,3-Bisphospho-glycerate3-Phospho-glycerate2-Phospho-glyceratePhosphoenol-pyruvate (PEP)PyruvateNADHNADHNADNADHHADPADPADPADPATPATPATPATPH2OH2OPPPPPPPPPPPPPP6.8 Pyruvate is oxidized prior to the citric acid cycleThe pyruvate formed in glycolysis is transported from the cytoplasm into a mitochondrion wherethe citric acid cycle andoxidative phosphorylation will occur.© 2012 Pearson Education, Inc.6.8 Pyruvate is oxidized prior to the citric acid cycleTwo molecules of pyruvate are produced for each molecule of glucose that enters glycolysis.Pyruvate does not enter the citric acid cycle, but undergoes some chemical grooming in whicha carboxyl group is removed and given off as CO2,the two-carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH,coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA, andacetyl CoA enters the citric acid cycle.© 2012 Pearson Education, Inc.Figure 6.8PyruvateCoenzyme AAcetyl coenzyme ANADNADHHCoACO23216.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 moleculesThe citric acid cycleis also called the Krebs cycle (after the German-British researcher Hans Krebs, who worked out much of this pathway in the 1930s),completes the oxidation of organic molecules, andgenerates many NADH and FADH2 molecules.© 2012 Pearson Education, Inc.Figure 6.9AAcetyl CoACitric Acid CycleCoACoACO2233NAD3 HNADHADPATPPFADFADH26.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 moleculesDuring the citric acid cyclethe two-carbon group of acetyl CoA is added to a four-carbon compound, forming citrate, citrate is degraded back to the four-carbon compound,two CO2 are released, and 1 ATP, 3 NADH, and 1 FADH2 are produced.© 2012 Pearson Education, Inc.6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 moleculesRemember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose.Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is2 ATP,6 NADH, and2 FADH2.© 2012 Pearson Education, Inc.Figure 6.9B_s1CoACoA1Acetyl CoAOxaloacetateCitric Acid Cycle2 carbons enter cycleStepAcetyl CoA stokesthe furnace.1Figure 6.9B_s2NADHNADHNADNADHHCO2CO2ATPADPPCoACoA321312Acetyl CoAOxaloacetateCitric Acid Cycle2 carbons enter cycleCitrateleaves cycleAlpha-ketoglutarateleaves cycleStepAcetyl CoA stokesthe furnace.Steps –NADH, ATP, and CO2are generated during redox reactions.Figure 6.9B_s3NADHNADHNADNADNADNADHHHHCO2CO2ATPADPPFADFADH2CoACoA3214534512Acetyl CoAOxaloacetateCitric Acid Cycle2 carbons enter cycleCitrateleaves cycleAlpha-ketoglutarateleaves cycleSuccinateMalateStepAcetyl CoA stokesthe furnace.Steps –NADH, ATP, and CO2are generated during redox reactions.Steps –Further redox reactions generateFADH2 and more NADH.6.10 Most ATP production occurs by oxidative phosphorylationOxidative phosphorylationinvolves electron transport and chemiosmosis andrequires an adequate supply of oxygen.© 2012 Pearson Education, Inc.6.10 Most ATP production occurs by oxidative phosphorylationElectrons from NADH and FADH2 travel down the electron transport chain to O2.Oxygen picks up H+ to form water.Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space.In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.© 2012 Pearson Education, Inc.Figure 6.10Oxidative PhosphorylationElectron Transport ChainChemiosmosisMito-chondrialmatrixInner mito-chondrialmembraneIntermem-branespaceElectronflowProteincomplexof electroncarriersMobileelectroncarriersATPsynthaseNADHNAD2 HFADH2FADO2H2OADPPATP12HHHHHHHHHHHIIIIIIIVFigure 6.10_1HHHHHHHHHHHOxidative PhosphorylationElectron Transport ChainChemiosmosisIIIIIIIVNADHNAD2 HFADH2FADO2H2OADPPATP21ElectronflowProteincomplexof electroncarriersMobileelectroncarriersATPsynthase6.11 CONNECTION: Interrupting cellular respiration can have both harmful and beneficial effectsThree categories of cellular poisons obstruct the process of oxidative phosphorylation. These poisonsblock the electron transport chain (for example, rotenone, cyanide, and carbon monoxide),inhibit ATP synthase (for example, the antibiotic oligomycin), ormake the membrane leaky to hydrogen ions (called uncouplers, examples include dinitrophenol).© 2012 Pearson Education, Inc.Figure 6.11ATPsynthaseNADNADHFADH2FADHHHHHHHH2 HH2OADPATPPO221RotenoneCyanide,carbon monoxideOligomycinDNP6.11 CONNECTION: Interrupting cellular respiration can have both harmful and beneficial effectsBrown fat isa special type of tissue associated with the generation of heat andmore abundant in hibernating mammals and newborn infants.© 2012 Pearson Education, Inc.6.11 CONNECTION: Interrupting cellular respiration can have both harmful and beneficial effectsIn brown fat,the cells are packed full of mitochondria,the inner mitochondrial membrane contains an uncoupling protein, which allows H+ to flow back down its concentration gradient without generating ATP, andongoing oxidation of stored fats generates additional heat.© 2012 Pearson Education, Inc.6.12 Review: Each molecule of glucose yields many molecules of ATPRecall that the energy payoff of cellular respiration involvesglycolysis,alteration of pyruvate,the citric acid cycle, andoxidative phosphorylation.© 2012 Pearson Education, Inc.6.12 Review: Each molecule of glucose yields many molecules of ATPThe total yield is about 32 ATP molecules per glucose molecule.This is about 34% of the potential energy of a glucose molecule.In addition, water and CO2 are produced.© 2012 Pearson Education, Inc.Figure 6.12NADHFADH2NADHFADH2NADHorNADHMitochondrionCYTOPLASMElectron shuttlesacross membraneGlycolysisGlucose2PyruvatePyruvateOxidation2 AcetylCoACitric AcidCycleOxidativePhosphorylation(electron transportand chemiosmosis)Maximumper glucose:by substrate-levelphosphorylationby substrate-levelphosphorylationby oxidativephosphorylation222262ATP2about28 ATPAboutATP32ATP2FERMENTATION: ANAEROBIC HARVESTING OF ENERGY© 2012 Pearson Education, Inc.6.13 Fermentation enables cells to produce ATP without oxygenFermentation is a way of harvesting chemical energy that does not require oxygen. Fermentationtakes advantage of glycolysis,produces two ATP molecules per glucose, andreduces NAD+ to NADH.The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+.© 2012 Pearson Education, Inc.6.13 Fermentation enables cells to produce ATP without oxygenYour muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in whichNADH is oxidized to NAD+ andpyruvate is reduced to lactate.© 2012 Pearson Education, Inc.Animation: Fermentation Overview6.13 Fermentation enables cells to produce ATP without oxygenLactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells.The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt.Other types of microbial fermentation turn soybeans into soy sauce and cabbage into sauerkraut.© 2012 Pearson Education, Inc.Figure 6.13A2 NAD2 NADH2 NAD2 NADH2 Lactate2 PyruvateGlucose2 ADP2 ATP2 PGlycolysis6.13 Fermentation enables cells to produce ATP without oxygenThe baking and winemaking industries have used alcohol fermentation for thousands of years.In this process yeasts (single-celled fungi)oxidize NADH back to NAD+ andconvert pyruvate to CO2 and ethanol.© 2012 Pearson Education, Inc.Figure 6.13B2 NAD2 NADH2 NAD2 NADH2 Ethanol2 PyruvateGlucose2 ADP2 ATP2 PGlycolysis2 CO26.13 Fermentation enables cells to produce ATP without oxygenObligate anaerobesare poisoned by oxygen, requiring anaerobic conditions, andlive in stagnant ponds and deep soils.Facultative anaerobesinclude yeasts and many bacteria, andcan make ATP by fermentation or oxidative phosphorylation.© 2012 Pearson Education, Inc.6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on EarthGlycolysis is the universal energy-harvesting process of life.The role of glycolysis in fermentation and respiration dates back tolife long before oxygen was present,when only prokaryotes inhabited the Earth, about 3.5 billion years ago.© 2012 Pearson Education, Inc.6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on EarthThe ancient history of glycolysis is supported by itsoccurrence in all the domains of life andlocation within the cell, using pathways that do not involve any membrane-bounded organelles.© 2012 Pearson Education, Inc.CONNECTIONS BETWEEN METABOLIC PATHWAYS© 2012 Pearson Education, Inc.6.15 Cells use many kinds of organic molecules as fuel for cellular respirationAlthough glucose is considered to be the primary source of sugar for respiration and fermentation, ATP is generated usingcarbohydrates,fats, andproteins.© 2012 Pearson Education, Inc.6.15 Cells use many kinds of organic molecules as fuel for cellular respirationFats make excellent cellular fuel because they contain many hydrogen atoms and thus many energy-rich electrons andyield more than twice as much ATP per gram than a gram of carbohydrate or protein. © 2012 Pearson Education, Inc.Figure 6.15Food, such aspeanutsSugarsGlycerolFatty acidsAmino acidsAminogroupsOxidativePhosphorylationCitricAcidCyclePyruvateOxidationAcetyl CoAATPGlucoseG3PPyruvateGlycolysisCarbohydratesFatsProteins6.16 Food molecules provide raw materials for biosynthesisCells use intermediates from cellular respiration for the biosynthesis of other organic molecules.© 2012 Pearson Education, Inc.Figure 6.16CarbohydratesFatsProteinsCells, tissues, organismsAmino acidsFatty acidsGlycerolSugarsAminogroupsCitricAcidCyclePyruvateOxidationAcetyl CoAATP neededto drivebiosynthesisATPGlucose SynthesisPyruvateG3PGlucose6.16 Food molecules provide raw materials for biosynthesisMetabolic pathways are often regulated by feedback inhibition in which an accumulation of product suppresses the process that produces the product.© 2012 Pearson Education, Inc.