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Chapter 9 Cellular Respiration: Harvesting Chemical Energy PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-2 Light energy Energy flow (one way) and chemical recycling in ecosystems ECOSYSTEM Photosynthesis in chloroplasts CO2 + H2O Organic +O molecules 2 Cellular respiration in mitochondria ATP ATP powers most cellular work Heat energy Catabolic Pathways and Production of ATP • The breakdown of organic molecules is exergonic – energy is released In exergonic reactions the energy stored in the reactants is greater than the energy stored in the products • Fermentation a catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid • Aerobic respiration consumes organic molecules and O2 and yields ATP • Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-UN2 becomes oxidized becomes reduced becomes oxidized becomes reduced Fig. 9-UN3 Oxidation of Organic Fuel Molecules During Cellular Respiration becomes oxidized becomes reduced Fig. 9-4 2 e– + 2 H+ 2 e– + H+ H+ NADH Dehydrogenase Reduction of NAD+ NAD+ + + H+ 2[H] Oxidation of NADH Nicotinamide (reduced form) Nicotinamide (oxidized form) NAD serves as an electron acceptor in cellular respiration to become NADH (stored energy). These electrons are “dropped off” at the electron transport chain ETC Fig. 9-5 H2 + 1/2 O2 2H (from food via NADH) Controlled release of + – 2H + 2e energy for synthesis of ATP 1/ 2 O2 Explosive release of heat and light energy 1/ (a) Uncontrolled reaction 2 O2 (b) Cellular respiration Electrons keep moving “downhill” because each carrier protein is more electronegative The Stages of Cellular Respiration: A Preview • Cellular respiration has three stages: – Glycolysis – occurs in the cytoplasm (breaks down glucose into two molecules of pyruvate) – The citric acid cycle – occurs in the mitochondrial matrix (completes the breakdown of glucose) – Oxidative phosphorylation – occurs on the inner mitochondrial membrane (accounts for most of the ATP synthesis) – Glycolysis and the citric acid cycle are examples of substrate-level phosphorylation – an enzyme transfers a phosphate from a substance to ADP (Fig. 9.7) – Oxidative phosphorylation (occurs in ETC) is powered by redox reactions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-6-3 Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion Cytosol ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation Fig. 9-7 Glycolysis and the citric acid cycle are examples of substrate-level phosphorylation – an enzyme transfers a phosphate from a substance to ADP Enzyme Enzyme ADP P Substrate + Product http://highered.mheducation.com/sites/0072507470/student_view0/chapter25/an imation__how_glycolysis_works.html This link will guide you through all the steps of cellular respiration ATP Fig. 9-8 Energy investment phase Glucose 2 ADP + 2 P 2 ATP used 4 ATP formed Energy payoff phase 4 ADP + 4 P 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H+ 2 Pyruvate + 2 H2O 2 ATP 2 NADH + 2 H+ Fig. 9-9-4 Coupling of reactions is the driving force that keeps glycolysis moving Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate 2 Phosphoglucoisomerase Fructose1, 6-bisphosphate 4 Fructose-6-phosphate ATP Aldolase 3 Phosphofructokinase ADP 5 Isomerase Fructose1, 6-bisphosphate 4 Aldolase 5 Isomerase Dihydroxyacetone phosphate Dihydroxyacetone phosphate Glyceraldehyde3-phosphate Glyceraldehyde3-phosphate Fig. 9-9-9 2 NAD+ 6 Triose phosphate dehydrogenase 2 Pi 2 NADH + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 Phosphoenolpyruvate 2 ADP 2 3-Phosphoglycerate 8 Phosphoglyceromutase 2 ATP 2 10 Pyruvate kinase 2-Phosphoglycerate 9 2 H2O Enolase 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 2 Pyruvate Pyruvate Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules • In the presence of O2, pyruvate enters the mitochondrion • Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-10 CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Acetyl CoA Pyruvate Transport protein CO2 Coenzyme A • The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix • The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn • Remember – Two turns take place for each 1 molecule of glucose, therefore a total of 2ATP, 6 NADH, and 2FADH2 are generated during the Krebs cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-11 Pyruvate Remember – To calculate the inputs and outputs on a perglucose basis, multiply by 2, because each glucose molecule is split during glycolysis into two pyruvate moleucles CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle FADH2 2 CO2 3 NAD+ 3 NADH FAD + 3 H+ ADP + P i ATP Fig. 9-12-8 Acetyl CoA CoA—SH NADH +H+ H2O 1 NAD+ 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD+ Citric acid cycle 7 H2O NADH + H+ 3 CO2 Fumarate CoA—SH 6 -Ketoglutarate 4 CoA—SH 5 FADH2 NAD+ FAD Succinate GTP GDP ADP ATP Pi Succinyl CoA NADH + H+ CO2 Concept 9.4: During 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Pathway of Electron Transport • The electron transport chain is in the cristae of the mitochondrion (inner mitochondrial membrane) • Most of the chain’s components are proteins, which exist in multiprotein complexes • The carriers alternate reduced and oxidized states as they accept and donate electrons • Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-13 This process, in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such the synthesis of ATP, is called chemiosmosis. We have previously used the word osmosis in discussing water transport, but here it refers to the flow of H+ across a membrane. NADH 50 2 e– NAD+ FADH2 2 e– 40 FMN FAD Multiprotein complexes FAD Fe•S Fe•S Q Cyt b 30 Fe•S Cyt c1 I V Cyt c Cyt a Cyt a3 20 10 2 e– (from NADH or FADH2) 0 2 H+ + 1/2 O2 H2O Fig. 9-14 INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Catalytic knob ADP + P i ATP MITOCHONDRIAL MATRIX Fig. 9-16 H+ H+ H+ H+ Protein complex of electron carriers Cyt c V Q ATP synthase FADH2 NADH 2 H+ + 1/2O2 H2O FAD NAD+ ADP + P i (carrying electrons from food) ATP H+ 1 Electron transport chain Oxidative phosphorylation 2 Chemiosmosis Fig. 9-17 Electron shuttles span membrane CYTOSOL 2 NADH Glycolysis Glucose 2 Pyruvate MITOCHONDRION 2 NADH or 2 FADH2 6 NADH 2 NADH 2 Acetyl CoA + 2 ATP Citric acid cycle + 2 ATP Maximum per glucose: About 36 or 38 ATP 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen • Most cellular respiration requires O2 to produce ATP • Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions), therefore this series of reactions evolved very early in prokaryotic organisms before oxygen was present in the atomosphere. • In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Types of Fermentation • Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis. This is important because there is only a limited supply of NAD+ in cells. • Two common types are alcohol fermentation and lactic acid fermentation • In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 • Alcohol fermentation by yeast is used in brewing, winemaking, and baking • In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2 • 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 scarce Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-18 2 ADP + 2 Pi http://www.dnatube.co m/video/5078/Fermenta tion-Anaerobicrespiration-Lactic-Acidand-Ethanol Glucose 2 ATP Glycolysis 2 Pyruvate 2 NAD+ 2 NADH + 2 H+ 2 CO2 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 Pi Glucose 2 ATP Glycolysis 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate 2 Lactate (b) Lactic acid fermentation Fermentation and Aerobic Respiration Compared • Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate • The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration • Cellular respiration produces 36/38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-19 Glucose CYTOSOL Glycolysis Pyruvate No O2 present: Fermentation O2 present: Aerobic cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle The Evolutionary Significance of Glycolysis • Glycolysis occurs in nearly all organisms • Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 9-20 Carbs., fats, and proteins can all be used as fuels for cellular respiration. Monomers of these molecules enter glycolysis or the citric acid cycler at various points. Glycolysis and the citric acid cycle are catabolic funnels through which electrons from all kinds of organic molecules flow on their exergonic fall to oxygen. Proteins Carbohydrates Amino acids Sugars Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation Fats Glycerol Fatty acids Fig. 9-21 Glucose AMP Enzymes at certain points in the respiratory pathway respond to inhibitors and activators that help set the pace of glycolysis and the citric acid cycle. This feedback regulation adjusts the rate of respiration as the cell’s catabolic and anabolic demands change. Glycolysis Fructose-6-phosphate – Stimulates + Phosphofructokinase – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Citric acid cycle Oxidative phosphorylation Fig. 9-UN8 Pg. 184 #10 Time Fig. 9-UN9