9 Cellular Respiration and Fermentation CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick Figure 9.1 Figure 9.2 Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 powers most cellular work Heat energy 1
Figure 9.2 Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Organic molecules + O 2 powers most cellular work Heat energy Figure 9.2 Light energy ECOSYSTEM CO 2 + H 2 O Organic molecules + O 2 powers most cellular work Heat energy Figure 9.2 cellular respiration Aerobic Concept ECOSYSTEM = 9.1: O Catabolic pathways yield 2 Anaerobic energy by = no O 2 oxidizing organic fuels CO 2 + H 2 O C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + Energy ( + heat) Organic molecules + O 2 Catabolic pathways exergonic Heat energy 2
Redox Reactions: Oxidation and Reduction The transfer of electrons during chemical reactions releases energy stored in organic molecules This released energy is ultimately used to synthesize The Principle of Redox Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions In oxidation, a substance loses electrons, or is oxidized In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced) Figure 9.UN03 becomes oxidized becomes reduced 3
glucose Cellular respiration C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + Energy ( + heat) 1) Glycolysis (glucose = 2 pyruvate) 2) The citric acid cycle (completes the breakdown of pyruvate) 3) Oxidative phosphorylation (accounts for most of the synthesis) 4) Substrate level phosphorylation Generation of during Cellular Respiration 1. Substrate Enzyme level phosphorylationenzyme transfer of phosphate group from an organic substrate to ADP This method makes very little of the generated in cellular respiration Substrate level phosphorylation synthesis by direct transfer of phosphate group from an organic fuel molecules to ADP Enzyme Enzyme ADP P Substrate Product 4
Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate PYRUVATE Glycolysis ( sugar splitting ) OXIDATIVE breaks PHOSPHORYL- OXIDATION down glucose (6 carbon) into 2 of ATION pyruvate (3 carbon) Glycolysis occurs in cytoplasm and whether or not O 2 is present Glycolysis has 2 major phases 1) Energy investment phase 2) Energy payoff phase 2 used 4 formed Total 2 formed Total 2 NADH formed NAD + picks up electron to become NADH Figure 9.8 Energy Investment Phase 2 used 2 ADP + 2 P Energy Payoff Phase 4 ADP + 4 P 4 formed 2 NAD + + 4 e + 4 2 NAD 2 2 + 2 H 2 O Net 4 formed 2 used 2 NAD + + 4 e + 4 2 + 2 H 2 O 2 2 NAD 2 5
Figure 9.9a 2 used : Energy Investment Phase Fructose 6-phosphate 6-phosphate ADP ADP Hexokinase Phosphoglucoisomerasfructokinase Phospho- 1 2 3 Fructose 1,6-bisphosphate Aldolase 4 Glyceraldehyde 3-phosphate (G3P) Isomerase 5 Dihydroxyacetone phosphate (DHAP) Figure 9.9b Total 2 NADH formed Substrate-level Substrate-level 4 formed : Energy Payoff Phase 2 NAD + 2 NADH + 2 2 2 2 H 2O 2 ADP 2 2 2 2 2 ADP 2 Triose Phosphoglycerokinasglyceromutase kinase Phospho- Enolase phosphate 2 dehydrogenase 9 7 8 10 Glyceraldehydglyceratglyceratglyceratpyruvate (PEP) 6 1,3-Bisphospho- 3-Phospho- 2-Phospho- Phosphoenol- 3-phosphate (G3P) Figure 9.6-1 2 NADH 2 CYTOSOL MITOCHONDRION 2 Substrate-level Phosphorylation 6
Muscle Protein FAT The Evolutionary Significance of Glycolysis Glycolysis is a very ancient process Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere Very little O 2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate Concept 9.3: After pyruvate is oxidized, the citric acid cycle completes the energyyielding oxidation of Muscle organic molecules If O 2 Present goes into mitochondria If O 2 Absent? Protein FAT 7
Figure 9.6-2 PYRUVATE OXIDATION CYTOSOL MITOCHONDRION Figure 9.10 multienzyme complex that catalyses three reactions CYTOSOL 1 CO 2 pyruvate (3C) acetyl Coenzyme A (acetyl CoA) (2C) Coenzyme A MITOCHONDRION 3 2 Transport protein NAD + NAD Figure 9.11 The Citric Acid Cycle PYRUVATE OXIDATION The cycle oxidizes organic fuel derived from pyruvate, generating 1, 3 NADH, and 1 FADH 2 per turn CO 2 8 steps (specific enzyme) oxaloacetate FADH 2 FAD CoA CoA CoA CoA Krebs cycle citrate 2 CO 2 3 NAD + 3 NADH + 3 ADP + P i Substrate-level 8
Figure 9.12-8 CoA-SH NADH + 1 NAD + Oxaloacetate 8 2 H 2O H 2O 7 Malate Citrate Isocitrate NAD + NADH 3 + CO 2 Fumarate 6 CoA-SH CoA-SH 4 -Ketoglutarate FADH 2 FAD Succinate GTP GDP ADP 5 P i Succinyl CoA NAD + NADH + CO 2 Fermentation Within cytoplasm Muscle If O 2 Absent? may still be metabolized in mito If some other O 2 substitute available e.g. sulfate, nitrate Anaerobic respiration goes into mitochondria If O 2 Present Glycolysis common FAT Protein Aerobic respiration Figure 9.18 CYTOSOL Glycolysis NADH fork No O 2 present: Fermentation O 2 present: Aerobic cellular respiration Ethanol, lactate, or other products MITOCHONDRION 9
Fermentation is a partial degradation of sugars that occurs without O 2 Muscle Protein FAT Concept 9.5: Fermentation and anaerobic respiration enable cells to produce without the use of oxygen Fermentation uses substrate-level phosphorylation to generate Two common types are alcohol fermentation and lactic acid fermentation Figure 9.17 regenerate NAD +, which can be reused by glycolysis. In alcohol fermentation, pyruvate is converted to ethanol in two steps 2 ADP + 2 P i 2 2 NAD + 2 NADH + 2 2 2 CO 2 2 ADP + 2 P i 2 The first step releases CO 2 The second step 2 NAD + 2 NADH produces ethanol + 2 2 2 Ethanol (a) Alcohol fermentation 2 Acetaldehyde 2 Lactate Alcohol fermentation by yeast is used in brewing, winemaking, and baking (b) Lactic acid fermentation 10
Figure 9.17 In lactic acid fermentation, pyruvate is reduced by NADH, forming lactate as an end product, with no release of CO ADP + 2 P 2 i 2 regenerate NAD +, which can be reused by glycolysis. 2 ADP + 2 P i 2 Lactic acid fermentation by some fungi and bacteria is 2 used to make cheese and 2 NAD + 2 NADH 2 yogurt CO 2 + 2 2 NAD + 2 NADH + 2 2 Human muscle cells use lactic acid fermentation to 2 Ethanol 2 Acetaldehyde 2 Lactate generate when O 2 is (a) Alcohol fermentation (b) Lactic acid fermentation scarce Comparing Fermentation with Anaerobic and Aerobic Respiration similarities All use glycolysis (net = 2) to oxidize glucose and harvest chemical energy of food In all three, NAD + is the oxidizing agent that accepts electrons during glycolysis differences The processes have different mechanisms for oxidizing NADH: In fermentation, an organic molecule (such as pyruvate or acetaldehyde) acts as a final electron acceptor In cellular respiration electrons are transferred to the electron transport chain Cellular respiration produces 32 per glucose molecule; fermentation produces 2 per glucose molecule 11
Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O 2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes Figure 9.18 CYTOSOL Glycolysis NADH fork No O 2 present: Fermentation O 2 present: Aerobic cellular respiration Ethanol, lactate, or other products MITOCHONDRION Figure 9.18 CYTOSOL Glycolysis NADH No O 2 present: Fermentation Why not just keep pyruvate? O 2 present: Aerobic cellular respiration Ethanol, lactate, or other products MITOCHONDRION 12
Figure 9.18 No O 2 present NAD Glycolysis NADH Ethanol, lactate, or other products X If pyruvate is not metabolized We would run out of NAD And die because of not enough energy MITOCHONDRION X X Animation: Fermentation Overview Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to synthesis Following glycolysis and the citric acid cycle, NADH and FADH 2 account for most of the energy extracted from food These two electron carriers donate electrons to the electron transport chain, which powers synthesis via oxidative phosphorylation 13
Free energy, G Free energy, G Figure 9.5 Unlike an uncontrolled reaction, H 2 + ½ the O 2 electron 2 ½ O 2 transport chain passes electrons in a series of steps Controlled instead of one explosive release of reaction 2 + 2 e energy O 2 pulls electrons Explosive down the chain in an energy-yielding release tumble 2 e The energy yielded is used to regenerate H 2 O 2 H 2 O ½ O 2 (a) Uncontrolled reaction (b) Cellular respiration Mitochondrion The electron transport chain is in Intermembrane the inner membrane (cristae) of space the mitochondrion Outer membrane Free ribosomes in the mitochondrial matrix (a) DNA Inner membrane Cristae Matrix 0.1 μm Figure 9.UN13 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 INTERMEMBRANE Electrons drop in free energy as they go down the chain SPACE and are finally passed to O 2, forming H 2 O Protein complex of electron carriers I II Q FADH 2 FAD III Cyt c IV 2 + ½ O 2 H 2 O NADH NAD + (carrying electrons from food) MITOCHONDRIAL MATRIX 14
Free energy (G) relative to O 2 (kcal/mol) 50 40 30 20 2 e NADH FMN NAD + FADH 2 Fe S I Q 2 e Fe S Cyt b FAD II Fe S III Multiprotein complexes Cyt c 1 Cyt c Cyt a IV Cyt a 3 Electrons are transferred from NADH or FADH 2 to the electron transport chain Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O 2 The electron transport chain generates no directly 10 0 e 2 (originally from NADH or FADH 2 ) 2 + ½ O 2 H 2O It breaks the large free-energy drop from food to O 2 into smaller steps that release energy in manageable amounts INTERMEMBRANE SPACE Protein complex of electron carriers I Q III Cyt c IV synthase II FADH 2 FAD 2 + ½ O 2 H 2O NADH NAD + ADP + P i (carrying electrons from food) 1 Electron transport chain MITOCHONDRIAL MATRIX 2 Chemiosmosis Oxidative phosphorylation Protein complex of electron carriers I Q III Cyt c IV II FADH 2 FAD 2 + ½ O 2 H 2O NADH NAD + ADP + P i (carrying electrons from food) 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation 15
Figure 9.14 INTERMEMBRANE SPACE Rotor Stator synthase Internal rod Catalytic knob ADP + P i MITOCHONDRIAL MATRIX protons synthase Chemiosmosis = the use of energy in a gradient to drive cellular work Protein complex of electron carriers I Q III Cyt c IV synthase II FADH 2 FAD 2 + ½ O 2 H 2O NADH NAD + ADP + P i (carrying electrons from food) 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation MITOCHONDRIAL MATRIX 16
Chemiosmosis = the use of energy in a gradient to drive cellular work Protein complex Cyt c The of electron energy stored in a gradient across a carriers IV Q transport I chain to III synthesis II FADH 2 FAD 2 + ½ O 2 H 2O synthase membrane couples the redox reactions of the electron The H+ gradient is referred to as a proton-motive NADH NAD + ADP + P i (carrying force, emphasizing its capacity to do work H electrons + from 1 Electron transport chain 2 Chemiosmosis food) Oxidative phosphorylation Chemiosmosis = the use of energy in a gradient to drive cellular work Protein complex of electron carriers Cyt c 2 + ½ O 2 H 2O synthase IV Q I III During cellular respiration, most energy flows in this sequence: II FADH 2 FAD NADH NAD glucose NAD electron transport chain ADP + P i proton-motive (carrying electrons force from food) 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation Why cyanide kills you? https://www.youtube.com/watch?v=fbxsjgxfnbu 17
Cyanide Binds and inhibits ETC Protein complex of electron carriers I Q III Cyt c IV synthase II FADH 2 FAD 2 + ½ O 2 H 2O NADH NAD + ADP + P i (carrying electrons from 1 Electron transport chain 2 Chemiosmosis food) No ETC = no cells - die of lack of energy Oxidative phosphorylation MITOCHONDRIAL MATRIX Cyanide Carbon Monoxide Why do adults shiver in cold? 18
Babies cannot shiver use brown fat to generate heat http://www.sciengist.com/newborn-human-babies-cantshiver-thats-why-they-have-brown-fat/ Cyanide Carbon Monoxide Uncouplers Figure 9.6-3 Electrons via NADH Electrons via NADH and FADH 2 PYRUVATE OXIDATION OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis) CYTOSOL MITOCHONDRION Substrate-level Substrate-level Oxidative 19
Figure 9.16 CYTOSOL 2 NADH 2 NADH or 2 FADH 2 2 NADH 6 NADH 2 FADH 2 MITOCHONDRION 2 PYRUVATE OXIDATION 2 OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis) + 2 + 2 + about 26 or 28 Maximum per glucose: About 30 or 32 About 34 % of energy in glucose BioFlix: Cellular Respiration Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration 20
Figure 9.19-1 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Figure 9.19-2 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glyceraldehyde 3- P NH 3 Figure 9.19-3 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids twice as much NH 3 Glyceraldehyde 3- P beta oxidation 21
Figure 9.19-4 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glyceraldehyde 3- P NH 3 Figure 9.19-5 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glyceraldehyde 3- P NH 3 OXIDATIVE PHOSPHORYLATION Regulation of Cellular Respiration via Feedback Mechanisms Inhibits Fructose 6-phosphate Phosphofructokinase Fructose 1,6-bisphosphate AMP Stimulates Inhibits low High Citrate citrate Oxidative phosphorylation 22