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Chapter 9 Cellular Respiration: Harvesting Chemical Energy PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings AP Biology Curriculum Standards Big Idea #2 Growth, reproduction and maintenance of the organization of living systems require free energy and matter. Essential Understanding 2A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter. Essential Knowledge 2.A.1 All living systems require constant input of free energy. 1. Order is maintained by constant free energy input into the system. 2. Loss of order or free energy flow results in death. 3. Increased disorder and entropy are offset by biological processes that maintain or increase order. Essential Knowledge 2.A.2 Organisms capture and store free energy for use in biological processes. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy Flow in Ecosystems – Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic CO2 + H2O + O2 Cellular molecules respiration in mitochondria ATP powers most cellular work Figure 9.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heat energy Section 9.1 Catabolic Pathways and Production of ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Catabolic Pathways • To keep working – Cells must regenerate ATP • Catabolic pathways yield energy by oxidizing organic fuels • The breakdown of organic molecules is exergonic • One catabolic process, fermentation – Is a partial degradation of sugars that occurs without oxygen Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Respiration • Is the most prevalent and efficient catabolic pathway • Consumes oxygen and organic molecules such as glucose • Yields ATP • Catabolic pathways yield energy – Due to the transfer of electrons – Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidation-Reduction Reactions (Redox) • Redox reactions – Transfer electrons from one reactant to another by oxidation and reduction – Coupling of oxidation – reduction reactions • In oxidation – A substance loses electrons, or is oxidized • In reduction – A substance gains electrons, or is reduced Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sample Redox Reaction • Examples of redox reactions becomes oxidized (loses electron) Na + Cl Na+ + becomes reduced (gains electron) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cl– Redox with electron sharing • Some redox reactions – Do not completely exchange electrons – Change the degree of electron sharing in covalent bonds Products Reactants becomes oxidized + CH4 CO 2O2 + Energy 2 H2O becomes reduced O O C O H O O H H H C + 2 H H Methane (reducing agent) Oxygen (oxidizing agent) Figure 9.3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Carbon dioxide Water Oxidation of Organic Fuel Molecules During Cellular Respiration • During cellular respiration – Glucose is oxidized and oxygen is reduced becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced • Stepwise energy harvest via NAD+ and the Electron Transport Chain - Oxidizes glucose in a series of steps Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Catabolism of Various Food Molecules • The catabolism of various molecules from food Proteins Carbohydrates Amino acids Sugars Fats Glycerol Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Figure 9.19 Oxidative phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fatty acids Electron Carriers • Electrons from organic compounds – Are usually first transferred to NAD+, a coenzyme 2 e– + 2 H+ NAD+ Dehydrogenase O NH2 H C CH2 O O– O O P O H – O P O HO O N+ Nicotinamide (oxidized form) H OH HO CH2 NH2 N N H O H HO N H OH N 2 e– + H+ H Reduction of NAD+ + 2[H] (from food) Oxidation of NADH NADH H O C H N NH2 + Nicotinamide (reduced form) NADH, the reduced form of NAD+ passes the electrons to the electron transport chain Figure 9.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why the Gradual Release of Energy? • If electron transfer is not stepwise – A large release of energy occurs – As in the reaction of hydrogen and oxygen to form water Thermite REDOX Rxn Figure 9.5 A Free energy, G H2 + 1/2 O2 Explosive release of heat and light energy H2O Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (a) Uncontrolled reaction Role of the Electron Transport Chain • The electron transport chain – Passes electrons in a series of steps instead of in one explosive reaction – Uses the energy from the electron transfer to 2H + / O form ATP 1 2 2 1/ O2 (from food via NADH) ETP & ATP Synthesis Free energy, G 2 H+ + 2 e– Controlled release of energy for synthesis of ATP ATP ATP ATP 2 e– 2 H+ H2O Figure 9.5 B Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Cellular respiration 2 The Stages of Cellular Respiration • Respiration is a cumulative function of three metabolic stages – Glycolysis – The citric acid cycle (or Krebs Cycle) – Oxidative phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of Stages of Aerobic Cellular Respiration • Glycolysis – Breaks down glucose into two molecules of pyruvate • The citric acid cycle – Completes the breakdown of glucose • Oxidative phosphorylation – Is driven by the electron transport chain – Generates ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of cellular respiration Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolsis Pyruvate Glucose Cytosol Mitochondrion ATP Figure 9.6 Oxidative phosphorylation: electron transport and chemiosmosis Substrate-level phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP Substrate-level phosphorylation ATP Oxidative phosphorylation Substrate-Level Phosphorylation • Both glycolysis and the citric acid cycle – Can generate ATP by substrate-level phosphorylation Enzyme Enzyme ADP P Substrate + Figure 9.7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Product ATP Concept 9.2: Glycolysis • Glycolysis harvests energy by oxidizing glucose to pyruvate • Glycolysis – Means “splitting of sugar” – Breaks down glucose into pyruvate – Occurs in the cytoplasm of the cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phases of Glycolysis • Glycolysis consists of two major phases – Energy investment phase – Energy payoff phase Citric acid cycle Glycolysis Oxidative phosphorylation ATP ATP ATP Energy investment phase Glucose 2 ATP + 2 P 2 ATP used Energy payoff phase 4 ADP + 4 P 2 NAD+ + 4 e- + 4 H + 4 ATP formed 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Glucose 4 ATP formed – 2 ATP used Figure 9.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 NAD+ + 4 e– + 4 H + 2 Pyruvate + 2 H2O 2 ATP + 2 H+ 2 NADH A Closer Look at the Phases 6 Triose phosphate dehydrogenase 2 NAD+ CH2OH HH H HO H HO OH H OH Glycolysis Citric Oxidative acid cyclephosphorylation 2 Pi 2 NADH + 2 H+ 2 Glucose P O C O CHOH ATP 1 CH2 O P 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase Hexokinase ADP CH2OH P HH OH OHH HO H OH 2 ATP O– 2 C CHOH Glucose-6-phosphate 2 CH2 O P 3-Phosphoglycerate 8 Phosphoglyceromutase Phosphoglucoisomerase CH2O P O CH2OH H HO HO H HO H 2 C Fructose-6-phosphate ATP O– O H C O 3 Phosphofructokinase ADP 2 2 P O CH2O CH2 O P HO H OH HO H Fructose1, 6-bisphosphate O– C O C O 4 Pyruvate kinase 2 ATP 5 H P O CH2 Isomerase C O C O CHOH CH2OH CH2 O P Figure 9.9 A Glyceraldehyde3-phosphate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings P CH2 Phosphoenolpyruvate 2 ADP 10 Aldolase Dihydroxyacetone phosphate P CH2OH 2-Phosphoglycerate 9 Enolase 2H O 2 O– C O C O Figure 9.8 B CH3 Pyruvate Overview of Glycolysis http://www.uic.edu/classes/bios/bios100/lectures/respiration.htm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of the Link Reaction http://www.uic.edu/classes/bios/bios100/lectures/respiration.htm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis IPOD Input: Processes: Output: Details/Description 1. Location: 2. Electron Carrier (s): 3. Purpose: 4. Next step: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.3: The Citric Acid Cycle • The citric acid cycle completes the energyyielding oxidation of organic molecules • The citric acid (or Krebs) cycle – Takes place in the matrix of the mitochondrion Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Link Reaction • Before the citric acid cycle can begin – Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis CYTOSOL MITOCHONDRION NAD+ NADH + H+ O– S CoA C O 2 C C O O 1 3 CH3 Pyruvate Transport protein Figure 9.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CH3 Acetyle CoA CO2 Coenzyme A TCA Overview • An overview of the citric acid cycle Pyruvate (from glycolysis, 2 molecules per glucose) Glycolysis Citric acid cycle ATP ATP Oxidative phosphorylatio n ATP CO2 CoA NADH + 3 H+ Acetyle CoA CoA CoA Citric acid cycle 2 CO2 3 NAD+ FADH2 FAD 3 NADH + 3 H+ ADP + P i ATP Figure 9.11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the citric acid cycle Glycolysis Citric Oxidative acid phosphorylation cycle S CoA C O CH3 Acetyl CoA CoA SH O NADH + H+ C COO– COO– 1 CH2 COO– NAD+ CH2 HO C COO– 8 Oxaloacetate CH2 COO– HO CH H2O COO– CH2 2 HC COO– COO– Malate HO Citrate CH2 COO– Isocitrate COO– H2O CH 7 COO– CH CO2 Citric acid cycle 3 NAD+ COO– Fumarate HC CH2 CoA SH 6 CoA SH COO– FAD CH2 CH2 COO– C O Succinate Pi S CoA GTP GDP Succinyl CoA ADP ATP Figure 9.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 C O COO– CH2 5 CH2 FADH2 COO– NAD+ NADH + H+ + H+ a-Ketoglutarate CH2 COO– NADH CO2 Overview of Citric Acid (Krebs) Cycle http://www.uic.edu/classes/bios/bios100/lectures/09_15_citric_acid_cycle-L.jpg Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Change in Free Energy During Glucose Breakdown http://www.uic.edu/classes/bios/bios100/lectures/respiration.htm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Citric Acid Cycle IPOD Input: Processes: Output: Details/Description 1. Location: 2. Electron Carrier (s): 3. Purpose: 4. Next step: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.4: Oxidative Phosphorylation • During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis • NADH and FADH2 – Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Pathway of Electron Transport • In the electron transport chain – • Electrons from NADH and FADH2 lose energy in several steps At the end of the chain – Electrons are passed to oxygen, forming water Free energy (G) relative to O2 (kcl/mol) 50 NADH FADH2 40 FMN I Fe•S FAD Fe•S II O 30 20 Multiprotein complexes III Cyt b Fe•S Cyt c1 IV Cyt c Cyt a Cyt a3 10 0 Figure 9.13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 H + + 12 O2 H2 O Chemiosmosis: The Energy-Coupling Mechanism • ATP synthase – Is the enzyme that actually makes ATP INTERMEMBRANE SPACE H+ H+ H+ H+ H+ H+ H+ A 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. H+ ADP + Pi Figure 9.14 MITOCHONDRIAL MATRIX Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP. The Electron Transport Chain • At certain steps along the electron transport chain – Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space • The resulting H+ gradient – Stores energy – Drives chemiosmosis in ATP synthase – Is referred to as a proton-motive force Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis • Chemiosmosis – Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis and the electron transport chain Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane ATP ATP H+ H+ H+ Intermembrane space Protein complex of electron carners Q I Inner mitochondrial membrane H+ Cyt c IV III FADH2 FAD+ NADH+ NAD+ 2 H+ + 1/2 O2 H2O ADP + (Carrying electrons from, food) Mitochondrial matrix ATP synthase II ATP Pi H+ Chemiosmosis Electron transport chain Electron transport and pumping of protons (H+), ATP synthesis powered by the flow which create an H+ gradient across the membrane Of H+ back across the membrane Figure 9.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative phosphorylation An Accounting of ATP Production by Cellular Respiration • During respiration, most energy flows in this sequence – Glucose to NADH to electron transport chain to proton-motive force to ATP • About 40% of the energy in a glucose molecule – Is transferred to ATP during cellular respiration, making approximately 38 ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Summary of ATP Production from Glucose Electron shuttles span membrane CYTOSOL MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH Glycolysis Glucose 2 Pyruvate 6 NADH Citric acid cycle 2 Acetyl CoA + 2 ATP by substrate-level phosphorylation Maximum per glucose: + 2 ATP by substrate-level phosphorylation 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol About 36 or 38 ATP Figure 9.16 • There are three main processes in this metabolic enterprise Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of the ETC http://www.uic.edu/classes/bios/bios100/lectures/09_21_electron_transport-L.jpg Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation IPOD Input: Processes: REDOX (Oxygen) Output: Details/Description 1. Location: 2. Electron Carrier (s): 3. Purpose: 4. Next step: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of Cellular Respiration http://www.uic.edu/classes/bios/bios100/lectures/respiration.htm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.5: Anaerobic Cellular Respiration • Fermentation enables some cells to produce ATP without the use of oxygen • Cellular respiration – Relies on oxygen to produce ATP • In the absence of oxygen – Cells can still produce ATP through fermentation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Aerobic or Anaerobic Respiration? http://www.uic.edu/classes/bios/bios100/lectures/09_24_energy_production-L.jpg Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis • Glycolysis – Can produce ATP with or without oxygen, in aerobic or anaerobic conditions – Couples with fermentation to produce ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Fermentation • Fermentation consists of – Glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis • In alcohol fermentation – Pyruvate is converted to ethanol in two steps, one of which releases CO2 • During lactic acid fermentation – Pyruvate is reduced directly to NADH to form lactate as a waste product Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Fermentation 2 ADP + 2 P1 2 ATP O– C O Glucose Glycolysis C O CH3 2 Pyruvate 2 NADH 2 NAD+ H 2 CO2 H H C OH C O CH3 CH3 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation 2 ADP + 2 Glucose P1 2 ATP Glycolysis O– C O C O O 2 NAD+ 2 NADH CH3 C O H C OH CH3 2 Lactate Figure 9.17 (b) Lactic acid fermentation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation and Cellular Respiration Compared • Both fermentation and cellular respiration – Use glycolysis to oxidize glucose and other organic fuels to pyruvate • Fermentation and cellular respiration – Differ in their final electron acceptor • Cellular respiration – Produces more ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation IPOD Input: Processes: Output: Details/Description 1. Location: 2. Electron Carrier (s): 3. Purpose: 4. Next step: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings