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生物醫學暨環境生物學系 鄭智美 助理教授 第一教學大樓 931室 電話 3121101- ext 2702 PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 9 Cellular Respiration: Harvesting Chemical Energy 細胞呼吸: 能量的產生 PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Key Concepts • Catabolic Pathways yield energy by oxidizing organic fuel • Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • The citric Acid cycle completes the energy yielding oxidation of organic molecules • Chemiosmosis couples electron transport to ATP synthesis • Fermentation enables some cels to produce ATP without the use of oxygen • Glycolysis and citric acid cycle connect to many other metabolic pathways Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Life Is Work • Living cells – Require transfusions of energy from outside sources to perform their many tasks – Obtains energy for its cells by eating plants Figure 9.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy flow and Chemical Recycling • Energy – Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic CO2 + H2O +O Cellular molecules 2 respiration in mitochondria AT P powers most cellular work Figure 9.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heat energ y Catabolic pathways yield energy by oxidizing organic fuels • The breakdown of organic molecules is exergonic Organic compound+ O2→CO2+ H2O+Energy • To keep working – Cells must regenerate ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Catabolic Pathways and Production of ATP • fermentation – Is a partial degradation of sugars that occurs without oxygen • Cellular respiration – Is the most prevalent and efficient catabolic pathway – Consumes oxygen and organic molecules such as glucose – Yields ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox Reactions: Oxidation and Reduction • Catabolic pathways yield energy – Due to the transfer of electrons Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Principle of Redox • Redox reactions – Transfer electrons from one reactant to another by oxidation and reduction • 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 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– Methane combustion as an energy yielding redox reaction • Some redox reactions – Do not completely exchange electrons – Change the degree of electron sharing in covalent bonds Products Reactants becomes oxidized + CH4 2O2 + 2 H2O Energy becomes reduced O O C O H O O H H H C + CO2 H H Methane (reducing agent) Figure 9.3 Oxygen (oxidizing agent) 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest via NAD+ and the Electron Transport Chain • Cellular respiration – Oxidizes glucose in a series of steps Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NAD+ as an electron shuttle • Electrons from organic compounds – Are usually first transferred to NAD+, a coenzyme 2 e– + 2 H+ 2 e– + 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 N H HO N H OH • NH2 N H O Reduction of NAD+ + 2[H] (from food) Oxidation of NADH N Figure 9.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H O C H N NH2 + Nicotinamide (reduced form) NADH, the reduced form of NAD+ – H NADH Passes the electrons to the electron transport chain The Uncontrolled Exergonic Reaction • If electron transfer is not stepwise – A large release of energy occurs – As in the reaction of hydrogen and oxygen to form water Free energy, G H2 + 1/2 O2 Figure 9.5 A Explosive release of heat and light energy H2O Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (a) Uncontrolled reaction Cellulae Respiration 2H • The electron transport chain 2 H+ + 2 e– – Uses the energy from the electron transfer to form ATP O2 Controlled release of energy for synthesis of ATP 1/ O2 ATP ATP ATP 2 e– 2 H+ H2O Figure 9.5 B Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 (from food via NADH) Free energy, G – Passes electrons in a series of steps instead of in one explosive reaction 1/ + (b) Cellular respiration 2 The Stages of Cellular Respiration: A Preview • Respiration is a cumulative function of three metabolic stages – 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 gure 9.6 Substrate-level phosphorylation Oxidative phosphorylation: electron transport and chemiosmosis ATP Substrate-level phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 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 Energy Input and Output of Glycolysis • Glycolysis consists of two major phases – Energy investment phase – Energy payoff phase Citric acid cycle Glycolysis ATP Oxidative phosphorylation 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 2 NADH formed + 2 H+ 2 Pyruvate + 2 H2O Glucose 4 ATP formed – 2 ATP used Figure 9.8 2 NAD+ + 4 e– + 4 H + Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 Pyruvate + 2 H2O 2 ATP + 2 H+ 2 NADH A closer look at the energy investment phase CH2OH H H H HO H HO OH H OH Glycolysis Glucose ATP 1 Hexokinase ADP CH2OH P O H H H OH H HO H OH Glucose-6-phosphate 2 Phosphoglucoisomerase CH2O P O HO H H CH2OH HO H HO Fructose-6-phosphate 3 ATP Phosphofructokinase ADP P O CH2 O CH2 HO H OH H HO O Fructose1, 6-bisphosphate P 4 Aldolase 5 P Figure 9.9 A O CH2 O C CH2OH Dihydroxyacetone phosphate Isomerase H C O CHOH CH2 O Glyceraldehyde3-phosphate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings P Citric acid cycle Oxidative phosphorylation A closer look at the energy payoff phase 6 Triose phosphate dehydrogenase 2 NAD+ 2 2 P Pi 2 NADH + 2 H+ O C O CHOH P CH2 O 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP O– 2 C CHOH O CH2 3-Phosphoglycerate 8 P Phosphoglyceromutase O– 2 C H 2 H2 O 2 O C O P CH2OH 2-Phosphoglycerate 9 Enolase O– C O C O P CH2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 Figure 9.8 B O– C O C O CH3 Pyruvate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The citric acid cycle completes the energy-yielding oxidation of organic molecules The citric acid cycle – Takes place in the matrix of the mitochondrion Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Conversion of pyruvate to Acetyl CoA, the junction beween glycolysis and the citric acid cycle • 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 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+ 8 Oxaloacetate HO C COO– COO– CH2 COO– HO CH H2O CH2 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 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Free Energy Change During Electron Transport • At the end of the chain – Electrons are passed to oxygen, forming water NADH 50 Free energy (G) relative to O2 (kcl/mol) FADH2 40 I FMN Multiprotein complexes FAD Fe•S Fe•S II O III Cyt b 30 Fe•S Cyt c1 IV Cyt c Cyt a Cyt a3 20 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. 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 – 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 IV III ATP synthase II FADH2 NADH+ Mitochondrial matrix H+ Cyt c FAD+ NAD+ 2 H+ + 1/2 O2 H2O ADP + (Carrying electrons from, food) ATP Pi H+ Chemiosmosis Electron transport chain + ATP synthesis powered by the flow Electron transport and pumping of protons (H ), + + 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There are three main processes in this metabolic enterprise 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 About 36 or 38 ATP Figure 9.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Accounting of ATP production by cellular respiration • 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 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 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 glyocolysis • In alcohol fermentation – Pyruvate is converted to ethanol in two steps, one of which releases CO2 • In 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 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 C O H C OH CH3 2 Lactate Figure 9.17 (b) Lactic acid fermentation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CH3 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 Pyruvate is a key juncture in catabolism Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Figure 9.18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acetyl CoA Citric acid cycle The Evolutionary Significance of Glycolysis • Glycolysis – Occurs in nearly all organisms – Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis and the citric acid cycle connect to many other metabolic pathways Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The catabolism of various molecules from food Proteins • Catabolic pathways Amino acids – Funnel electrons from many kinds of organic molecules into cellular respiration Carbohydrates Sugars Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Figure 9.19 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative phosphorylation Fats Glycerol Fatty acids Biosynthesis (Anabolic Pathways) • The body – Uses small molecules to build other substances • These small molecules – May come directly from food or through glycolysis or the citric acid cycle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Cellular Respiration via Feedback Mechanisms Glucose Glycolysis • Cellular respiration – Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle Fructose-6-phosphate – Inhibits Stimulates + Phosphofructokinase – Fructose-1,6-bisphosphate Inhibits Pyruvate Citrate ATP Acetyl CoA Citric acid cycle Figure 9.20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings AMP Oxidative phosphorylation