Cellular Respiration and Fermentation 7 Cellular Respiration and Fermentation

© 2014 Pearson Education, Inc.

Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic Figure 7.2 Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic molecules CO2  H2O  O2 Cellular respiration in mitochondria Figure 7.2 Energy flow and chemical recycling in ecosystems ATP powers most cellular work ATP Heat energy 3

Concept 7.1: Catabolic pathways yield energy by oxidizing organic fuels Fermentation - partial degradation of sugars without O2 Aerobic respiration - degradation of sugars with O2 Anaerobic respiration - similar to aerobic respiration but consumes compounds other than O2 © 2014 Pearson Education, Inc. 4

C6H12O6  6 O2  6 CO2  6 H2O  Energy (ATP) Cellular respiration includes both aerobic and anaerobic respiration but usually refers to aerobic Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose C6H12O6  6 O2  6 CO2  6 H2O  Energy (ATP) © 2014 Pearson Education, Inc. 5

The Principle of Redox Redox reactions (oxidation-reduction) reactions that transfer electrons between reactants Oxidation - substance loses electrons Reduction - substance gains electrons © 2014 Pearson Education, Inc. 6

Oxidation and reduction always occur together As one chemical is oxidized, the electrons it loses are always transferred to another chemical, reducing it

becomes oxidized (loses electron) becomes reduced (gains electron) Figure 7.UN01 becomes oxidized (loses electron) becomes reduced (gains electron) Figure 7.UN01 In-text figure, NaCl redox reaction, p. 136 8

becomes oxidized becomes reduced Figure 7.UN03 becomes oxidized becomes reduced Figure 7.UN03 In-text figure, cellular respiration redox reaction, p. 137 9

Helpful hint: think in terms of the gain or loss of hydrogen atoms Transfer of hydrogen atoms involves the transfer of electrons H = H+ + e- When a molecule loses a hydrogen atom, it becomes oxidized

The more reduced a molecule is, the more energy is stored its bonds

If you swallow glucose, enzymes in your cells will lower the activation energy, allowing the sugar to be oxidized in a series of steps. If it were released all at once, it would not be harvested efficiently.

SO… Hydrogen atoms (and e-) are not directly transferred to the oxygen Cells use the coenzyme NAD as an electron carrier in redox reactions NAD: nicotinamide adenine dinucleotide

NAD exists as: NAD+ oxidized form NADH reduced form NAD+ + H+ + 2 e- → NADH

Stepwise Energy Harvest via NAD+ and the Electron Transport Chain electron acceptor Coenzyme reduced form (NADH) passes electrons to electron transport chain to produce ATP https://www.youtube.com/watch?v=Kb-4uuCYLvE © 2014 Pearson Education, Inc. 16

NAD Nicotinamide (oxidized form) Figure 7.4a Figure 7.4a NAD+ as an electron shuttle (part 1: NAD+ structure) 17

2 e− 2 H 2 e−  H NAD NADH H Dehydrogenase Reduction of NAD Figure 7.4 2 e− 2 H 2 e−  H NAD NADH H Dehydrogenase Reduction of NAD  2[H] (from food)  H Oxidation of NADH Nicotinamide (reduced form) Nicotinamide (oxidized form) Figure 7.4 NAD+ as an electron shuttle 18

2 e−  2 H 2 e−  H H NADH Dehydrogenase Reduction of NAD   2[H] Figure 7.4b 2 e−  2 H 2 e−  H H NADH Dehydrogenase Reduction of NAD  2[H] (from food)  H Oxidation of NADH Nicotinamide (reduced form) Figure 7.4b NAD+ as an electron shuttle (part 2: NAD+ reaction) 19

Substrate-level phosphorylation is directly phosphorylating ADP with a phosphate and energy provided from a coupled reaction. SLP will only occur if there is a reaction that releases sufficient energy to allow the direct phosphorylation of ADP. Oxidative phosphorylation is when ATP is generated from the oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping of protons. generates an electrochemical gradient

The Stages of Cellular Respiration: A Preview Glycolysis (breaks down glucose into 2 pyruvate) (color-coded teal throughout the chapter) Pyruvate oxidation and the citric acid cycle (color-coded salmon) Oxidative phosphorylation (color-coded violet) Animation: Cellular Respiration © 2014 Pearson Education, Inc. 21

Electrons via NADH Glycolysis Glucose Pyruvate CYTOSOL MITOCHONDRION Figure 7.6-1 Electrons via NADH Glycolysis Glucose Pyruvate CYTOSOL MITOCHONDRION Figure 7.6-1 An overview of cellular respiration (step 1) ATP Substrate-level 22

Electrons via NADH and FADH2 Electrons via NADH Pyruvate oxidation Figure 7.6-2 Electrons via NADH and FADH2 Electrons via NADH Pyruvate oxidation Glycolysis Citric acid cycle Glucose Pyruvate Acetyl CoA CYTOSOL MITOCHONDRION Figure 7.6-2 An overview of cellular respiration (step 2) ATP ATP Substrate-level Substrate-level 23

Electrons via NADH and FADH2 Electrons via NADH Oxidative Figure 7.6-3 Electrons via NADH and FADH2 Electrons via NADH Oxidative phosphorylation: electron transport and chemiosmosis Pyruvate oxidation Glycolysis Citric acid cycle Glucose Pyruvate Acetyl CoA CYTOSOL MITOCHONDRION Figure 7.6-3 An overview of cellular respiration (step 3) ATP ATP ATP Substrate-level Substrate-level Oxidative 24

Concept 7.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis breaks glucose into 2 pyruvate occurs in cytoplasm … 2 phases Energy investment phase Energy payoff phase occurs whether or not O2 is present © 2014 Pearson Education, Inc. 25

Citric acid cycle Oxidative phosphorylation Pyruvate oxidation Figure 7.UN06 Citric acid cycle Oxidative phosphorylation Pyruvate oxidation Glycolysis Figure 7.UN06 In-text figure, mini-map, glycolysis, p. 140 ATP ATP ATP 26

Energy Investment Phase Figure 7.8 Energy Investment Phase Glucose 2 ADP  2 P 2 ATP used Energy Payoff Phase 4 ADP  4 P 4 ATP formed 2 NAD  4 e−  4 H 2 NADH  2 H Figure 7.8 The energy input and output of glycolysis 2 Pyruvate  2 H2O Net Glucose 2 Pyruvate  2 H2O 4 ATP formed − 2 ATP used 2 ATP 2 NAD  4 e−  4 H 2 NADH  2 H 27

Glycolysis: Energy Investment Phase Figure 7.9a Glycolysis: Energy Investment Phase Glyceraldehyde 3-phosphate (G3P) ATP Glucose 6-phosphate Fructose 6-phosphate ATP Fructose 1,6-bisphosphate Glucose ADP ADP Isomerase 5 Hexokinase Phosphogluco- isomerase Phospho- fructokinase Aldolase Dihydroxyacetone phosphate (DHAP) 1 4 2 3 Figure 7.9a A closer look at glycolysis (part 1: investment phase) 28

Glycolysis: Energy Investment Phase Figure 7.9aa-1 Glycolysis: Energy Investment Phase Glucose Figure 7.9aa-1 A closer look at glycolysis (part 1a, step 1) 29

Glycolysis: Energy Investment Phase Figure 7.9aa-2 Glycolysis: Energy Investment Phase ATP Glucose 6-phosphate Glucose ADP Hexokinase 1 Figure 7.9aa-2 A closer look at glycolysis (part 1a, step 2) 30

1. Enzyme transfers a phosphate group from ATP to glucose

Glycolysis: Energy Investment Phase Figure 7.9aa-3 Glycolysis: Energy Investment Phase ATP Glucose 6-phosphate Fructose 6-phosphate Glucose ADP Hexokinase Phosphogluco- isomerase 1 Figure 7.9aa-3 A closer look at glycolysis (part 1a, step 3) 2 32

Glycolysis: Energy Investment Phase Figure 7.9ab-1 Glycolysis: Energy Investment Phase Fructose 6-phosphate Figure 7.9ab-1 A closer look at glycolysis (part 1b, step 1) 33

Glycolysis: Energy Investment Phase Figure 7.9ab-2 Glycolysis: Energy Investment Phase Fructose 6-phosphate Fructose 1,6-bisphosphate ATP ADP Phospho- fructokinase Figure 7.9ab-2 A closer look at glycolysis (part 1b, step 2) 3 34

3. Enzyme transfers a phosphate group from a second ATP

Glycolysis: Energy Investment Phase Figure 7.9ab-3 Glycolysis: Energy Investment Phase Glyceraldehyde 3-phosphate (G3P) Fructose 6-phosphate Fructose 1,6-bisphosphate ATP ADP Isomerase 5 Phospho- fructokinase Aldolase Dihydroxyacetone phosphate (DHAP) 4 Figure 7.9ab-3 A closer look at glycolysis (part 1b, step 3) 3 36

4. Enzyme cleaves the sugar molecule into two different three-carbon sugars

Glycolysis: Energy Payoff Phase Figure 7.9b Glycolysis: Energy Payoff Phase 2 ATP 2 ATP 2 NADH 2 H2O Glyceraldehyde 3-phosphate (G3P) 2 ADP 2 NAD  2 H 2 ADP 2 2 2 2 2 Triose phosphate dehydrogenase Phospho- glycerokinase Phospho- glyceromutase Enolase Pyruvate kinase 2 P i 9 1,3-Bisphospho- glycerate 7 3-Phospho- glycerate 8 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) 10 Pyruvate 6 Figure 7.9b A closer look at glycolysis (part 2: payoff phase) 38

Glycolysis: Energy Payoff Phase Figure 7.9ba-1 Glycolysis: Energy Payoff Phase Glyceraldehyde 3-phosphate (G3P) Isomerase 5 Aldolase Dihydroxyacetone phosphate (DHAP) 4 Figure 7.9ba-1 A closer look at glycolysis (part 2a, step 1) 39

Glycolysis: Energy Payoff Phase Figure 7.9ba-2 Glycolysis: Energy Payoff Phase 2 NADH Glyceraldehyde 3-phosphate (G3P) 2 NAD  2 H 2 Triose phosphate dehydrogenase 2 P i Isomerase 1,3-Bisphospho- glycerate 5 6 Aldolase Dihydroxyacetone phosphate (DHAP) 4 Figure 7.9ba-2 A closer look at glycolysis (part 2a, step 2) 40

6. Two reactions occur: Sugar is oxidized by the transfer of electrons to NAD+, forming NADH A phosphate is attached to the oxidized substrate

Glycolysis: Energy Payoff Phase Figure 7.9ba-3 Glycolysis: Energy Payoff Phase 2 ATP 2 NADH Glyceraldehyde 3-phosphate (G3P) 2 NAD  2 H 2 ADP 2 2 Triose phosphate dehydrogenase Phospho- glycerokinase 2 P i Isomerase 1,3-Bisphospho- glycerate 7 3-Phospho- glycerate 5 6 Aldolase Dihydroxyacetone phosphate (DHAP) 4 Figure 7.9ba-3 A closer look at glycolysis (part 2a, step 3) 42

7. the phosphate group is transferred to ADP (substrate-level phosphorylation) 8. Enzyme relocates the remaining phosphate

Glycolysis: Energy Payoff Phase Figure 7.9bb-1 Glycolysis: Energy Payoff Phase 2 3-Phospho- glycerate Figure 7.9bb-1 A closer look at glycolysis (part 2b, step 1) 44

Glycolysis: Energy Payoff Phase Figure 7.9bb-2 Glycolysis: Energy Payoff Phase 2 H2O 2 2 2 Phospho- glyceromutase Enolase 9 3-Phospho- glycerate 8 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) Figure 7.9bb-2 A closer look at glycolysis (part 2b, step 2) 45

Glycolysis: Energy Payoff Phase Figure 7.9bb-3 Glycolysis: Energy Payoff Phase 2 ATP 2 H2O 2 ADP 2 2 2 2 Phospho- glyceromutase Enolase Pyruvate kinase 9 3-Phospho- glycerate 8 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) 10 Pyruvate Figure 7.9bb-3 A closer look at glycolysis (part 2b, step 3) 46

10. P is transferred from PEP to ADP forming ATP

ENERGY-REQUIRING STEPS fructose–1,6–bisphosphate Glycolysis ENERGY-REQUIRING STEPS OF GLYCOLYSIS glucose ATP 2 ATP invested ADP P glucose–6–phosphate P fructose–6–phosphate ATP ADP P P fructose–1,6–bisphosphate DHAP Fig. 8-4b, p.127

ENERGY-RELEASING STEPS 1,3–bisphosphoglycerate 1,3–bisphosphoglycerate Glycolysis ENERGY-RELEASING STEPS OF GLYCOLYSIS P P PGAL PGAL NAD+ NAD+ NADH NADH Pi Pi P P P P 1,3–bisphosphoglycerate 1,3–bisphosphoglycerate substrate-level phsphorylation ADP ADP ATP ATP 2 ATP PRODUCED P P 3–phosphoglycerate 3–phosphoglycerate Fig. 8-4c, p.127

Glycolysis P P 2–phosphoglycerate 2–phosphoglycerate H2O H2O P P PEP substrate-level phsphorylation ADP ADP ATP ATP 2 ATP produced pyruvate pyruvate Fig. 8-4d, p.127

Net Yield of Energy for Glycolysis: 2 ATP 2 NADH

Concept 7.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules Pyruvate enters mitochondrion (when O2 is present) It is converted to acetyl coenzyme A (acetyl CoA), which enters citric acid (Krebs) cycle Completes breakdown to CO2 generating 1 ATP, 3 NADH, and 1 FADH2 per turn © 2014 Pearson Education, Inc. 52

Citric acid cycle Oxidative phosphorylation Pyruvate oxidation Figure 7.UN07 Citric acid cycle Oxidative phosphorylation Pyruvate oxidation Glycolysis Figure 7.UN07 In-text figure, mini-map, pyruvate oxidation, p. 142 ATP ATP ATP 53

2 molecules per glucose) CYTOSOL Figure 7.10a Pyruvate (from glycolysis, 2 molecules per glucose) CYTOSOL CO2 NAD CoA Figure 7.10a An overview of pyruvate oxidation and the citric acid cycle (part 1: pyruvate oxidation) NADH  H Acetyl CoA MITOCHONDRION CoA 54

Enzymes remove CO2 and oxidize the remaining fragment, forming NADH from NAD+ Forms acetyl coenzyme A (acetyl CoA)

Citric acid cycle Figure 7.10 Pyruvate (from glycolysis, 2 molecules per glucose) CYTOSOL CO2 NAD CoA NADH  H Acetyl CoA MITOCHONDRION CoA CoA Citric acid cycle Figure 7.10 An overview of pyruvate oxidation and the citric acid cycle 2 CO2 FADH2 3 NAD FAD 3 NADH  3 H ADP  P i ATP 56

Citric acid cycle Acetyl CoA CoA CoA 2 CO2 FADH2 3 NAD 3 NADH FAD Figure 7.10b Acetyl CoA CoA CoA Citric acid cycle 2 CO2 FADH2 3 NAD Figure 7.10b An overview of pyruvate oxidation and the citric acid cycle (part 2: citric acid cycle) 3 NADH FAD  3 H ADP  P i ATP 57

Citric acid cycle Oxidative phosphorylation Pyruvate oxidation Figure 7.UN08 Citric acid cycle Oxidative phosphorylation Pyruvate oxidation Glycolysis Figure 7.UN08 In-text figure, mini-map, citric acid cycle, p. 143 ATP ATP ATP 58

next steps decompose citrate back to oxaloacetate, … a cycle 1. Acetyl CoA adds its two-carbon group to oxaloacetate producing citrate next steps decompose citrate back to oxaloacetate, … a cycle each step catalyzed by a specific enzyme It is a series of redox reactions NADH and FADH2 relay electrons to electron transport chain which powers ATP synthesis via oxidative phosphorylation © 2014 Pearson Education, Inc. 59

Citric acid cycle Figure 7.11-1 Acetyl CoA 1 Oxaloacetate 2 Citrate CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate Citric acid cycle Figure 7.11-1 A closer look at the citric acid cycle (steps 1-2) 60

Citric acid cycle Figure 7.11-2 Acetyl CoA 1 Oxaloacetate 2 Citrate CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle 3 NADH  H CO2 -Ketoglutarate Figure 7.11-2 A closer look at the citric acid cycle (step 3) 61

Citric acid cycle Figure 7.11-3 Acetyl CoA 1 Oxaloacetate 2 Citrate CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle 3 NADH  H CO2 CoA-SH -Ketoglutarate Figure 7.11-3 A closer look at the citric acid cycle (step 4) 4 CO2 NAD NADH Succinyl CoA  H 62

Citric acid cycle Figure 7.11-4 Acetyl CoA 1 Oxaloacetate 2 Citrate CoA-SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD Citric acid cycle 3 NADH  H CO2 CoA-SH -Ketoglutarate Figure 7.11-4 A closer look at the citric acid cycle (step 5) 4 CoA-SH 5 CO2 NAD Succinate P NADH i GTP GDP Succinyl CoA  H ADP ATP formation ATP 63

Citric acid cycle Figure 7.11-5 Acetyl CoA 1 Oxaloacetate 2 Malate CoA-SH 1 H2O Oxaloacetate 2 Malate Citrate Isocitrate NAD Citric acid cycle 3 NADH 7  H H2O CO2 Fumarate CoA-SH -Ketoglutarate Figure 7.11-5 A closer look at the citric acid cycle (steps 6-7) 6 4 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P NADH i GTP GDP Succinyl CoA  H ADP ATP formation ATP 64

Citric acid cycle Figure 7.11-6 Acetyl CoA 1 Oxaloacetate 8 2 Malate CoA-SH NADH 1  H H2O NAD Oxaloacetate 8 2 Malate Citrate Isocitrate NAD Citric acid cycle 3 NADH 7  H H2O CO2 Fumarate CoA-SH -Ketoglutarate Figure 7.11-6 A closer look at the citric acid cycle (step 8) 6 4 CoA-SH 5 FADH2 CO2 NAD FAD Succinate P NADH i GTP GDP Succinyl CoA  H ADP ATP formation ATP 65

NADH and FADH2 shuttle electrons (and H+) to the next phase Used to convert ADP to ATP

Diagram from book:

Start: Acetyl CoA adds its two-carbon group to oxaloacetate, producing Figure 7.11a Start: Acetyl CoA adds its two-carbon group to oxaloacetate, producing citrate; this is a highly exergonic reaction. Acetyl CoA CoA-SH 1 H2O Oxaloacetate Figure 7.11a A closer look at the citric acid cycle (part 1) 2 Citrate Isocitrate 69

Isocitrate is oxidized; NAD is reduced. Figure 7.11b Isocitrate Redox reaction: Isocitrate is oxidized; NAD is reduced. NAD NADH 3  H CO2 CO2 release CoA-SH -Ketoglutarate 4 Figure 7.11b A closer look at the citric acid cycle (part 2) CO2 release CO2 NAD Redox reaction: After CO2 release, the resulting four-carbon molecule is oxidized (reducing NAD), then made reactive by addition of CoA. NADH Succinyl CoA  H 70

Succinate is oxidized; FAD is reduced. Figure 7.11c Fumarate 6 CoA-SH 5 FADH2 FAD Redox reaction: Succinate is oxidized; FAD is reduced. Succinate P i GTP GDP Succinyl CoA Figure 7.11c A closer look at the citric acid cycle (part 3) ADP ATP formation ATP 71

Redox reaction: Malate is oxidized; NAD is reduced. Oxaloacetate 8 Figure 7.11d Redox reaction: Malate is oxidized; NAD is reduced. NADH  H NAD 8 Oxaloacetate Malate 7 Figure 7.11d A closer look at the citric acid cycle (part 4) H2O Fumarate 72

The Pathway of Electron Transport The electron transport chain is in the inner membrane (cristae) of the mitochondrion © 2014 Pearson Education, Inc. 73

Carriers alternate between being reduced and oxidized (accept and donate electrons)

Electron transport chain produces no ATP directly It breaks the large free-energy drop from food to O2 in small steps that releasing energy in manageable amounts

Oxidative phosphorylation: electron transport and chemiosmosis Citric Figure 7.UN09 Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle Pyruvate oxidation Glycolysis Figure 7.UN09 In-text figure, mini-map, oxidative phosphorylation, p. 144 ATP ATP ATP 77

Free energy (G) relative to O2 (kcal/mol) Figure 7.12 NADH 50 2 e− NAD FADH2 Multiprotein complexes 2 e− FAD 40 I FMN II Fe•S Fe•S Q III Cyt b 30 Fe•S Cyt c1 IV Free energy (G) relative to O2 (kcal/mol) Cyt c Cyt a Cyt a3 20 Figure 7.12 Free-energy change during electron transport 10 2 e− (originally from NADH or FADH2) 2 H  ½ O2 H2O 78

Free energy (G) relative to O2 (kcal/mol) Figure 7.12a NADH 50 2 e− NAD FADH2 2 e− FAD Multiprotein complexes I 40 FMN II Fe•S Fe•S Q III Cyt b Free energy (G) relative to O2 (kcal/mol) Fe•S 30 Cyt c1 IV Cyt c Figure 7.12a Free-energy change during electron transport (part 1) Cyt a Cyt a3 20 2 e− 10 79

Free energy (G) relative to O2 (kcal/mol) Figure 7.12b 30 Cyt c1 IV Cyt c Cyt a Cyt a3 20 Free energy (G) relative to O2 (kcal/mol) 2 e− 10 (originally from NADH or FADH2) Figure 7.12b Free-energy change during electron transport (part 2) 2 H  ½ O2 H2O 80

Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in transport chain pump H from the mitochondrial matrix to the intermembrane space (against their concentration gradient) The H gradient is referred to as a proton-motive force, emphasizing capacity to do work H move back across the membrane through ATP synthase © 2014 Pearson Education, Inc. 81

ATP synthase uses H flow to phosphorylate ATP This is an example of chemiosmosis, (use of H gradient energy to drive cellular work) Produces about 32 ATP

H INTERMEMBRANE SPACE Stator Rotor Internal rod Catalytic knob ADP  Figure 7.13 H INTERMEMBRANE SPACE Stator Rotor Internal rod Catalytic knob Figure 7.13 ATP synthase, a molecular mill ADP  P ATP MITOCHONDRIAL MATRIX i 83

Oxidative phosphorylation: electron transport and chemiosmosis Citric Figure 7.UN09 Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle Pyruvate oxidation Glycolysis Figure 7.UN09 In-text figure, mini-map, oxidative phosphorylation, p. 146 ATP ATP ATP 84

Electron transport chain Oxidative phosphorylation Figure 7.14 H H Protein complex of electron carriers H H Cyt c IV Q III I ATP synthase II 2 H  ½ O2 H2O FADH2 FAD NADH NAD Figure 7.14 Chemiosmosis couples the electron transport chain to ATP synthesis ADP  P ATP i (carrying electrons from food) H 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation 85

Electron transport chain Figure 7.14a H H Protein complex of electron carriers H Cyt c IV Q III I II 2 H  ½ O2 H2O FADH2 FAD Figure 7.14a Chemiosmosis couples the electron transport chain to ATP synthesis (part 1: electron transport chain) NAD NADH (carrying electrons from food) 1 Electron transport chain 86

2 ATP synthase Chemiosmosis H H ADP  ATP i P Figure 7.14b Figure 7.14b Chemiosmosis couples the electron transport chain to ATP synthesis (part 2: chemiosmosis) ADP  P ATP i H 2 Chemiosmosis 87

An Accounting of ATP Production by Cellular Respiration cellular respiration, most energy flows: glucose  NADH  electron transport chain  proton-motive force  ATP About 34% of energy transferred to ATP, making about 32 ATP There are several reasons why the number of ATP molecules is not known exactly © 2014 Pearson Education, Inc. 88

Electron shuttles span membrane MITOCHONDRION 2 NADH CYTOSOL or Figure 7.15 Electron shuttles span membrane MITOCHONDRION 2 NADH CYTOSOL or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Glycolysis Pyruvate oxidation 2 Acetyl CoA Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Pyruvate Glucose  2 ATP Figure 7.15 ATP yield per molecule of glucose at each stage of cellular respiration  2 ATP  about 26 or 28 ATP About 30 or 32 ATP Maximum per glucose: 89

Electron shuttles span membrane 2 NADH or 2 FADH2 2 NADH Glycolysis 2 Figure 7.15a Electron shuttles span membrane 2 NADH or 2 FADH2 2 NADH Glycolysis 2 Pyruvate Glucose Figure 7.15a ATP yield per molecule of glucose at each stage of cellular respiration (part 1: glycolysis)  2 ATP 90

Pyruvate oxidation 2 Acetyl CoA Citric acid cycle Figure 7.15b 2 NADH 6 NADH 2 FADH2 Pyruvate oxidation 2 Acetyl CoA Citric acid cycle Figure 7.15b ATP yield per molecule of glucose at each stage of cellular respiration (part 2: citric acid cycle)  2 ATP 91

2 NADH or 2 FADH2 2 NADH 6 NADH 2 FADH2 Oxidative phosphorylation: Figure 7.15c 2 NADH or 2 FADH2 2 NADH 6 NADH 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Figure 7.15c ATP yield per molecule of glucose at each stage of cellular respiration (part 3: oxidative phosphorylation)  about 26 or 28 ATP 92

About Maximum per glucose: 30 or 32 ATP Figure 7.15d Figure 7.15d ATP yield per molecule of glucose at each stage of cellular respiration (part 4: yield per glucose) 93

Concept 7.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Without O2 In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP © 2014 Pearson Education, Inc. 94

Anaerobic respiration uses final electron acceptor other than O2, for example, sulfate Still uses an electron transport chain Fermentation uses substrate-level phosphorylation instead of electron transport chain to generate ATP © 2014 Pearson Education, Inc. 95

Types of Fermentation Fermentation - glycolysis plus reactions that regenerate NAD, (can be reused by glycolysis) 2 common types: alcohol fermentation lactic acid fermentation © 2014 Pearson Education, Inc. 96

alcohol fermentation: pyruvate converted to ethanol Step 1 releases CO2 from pyruvate Step 2 reduces acetaldehyde to ethanol (by NADH) Alcohol fermentation by yeast used in brewing, winemaking, and baking © 2014 Pearson Education, Inc. 97

(a) Alcohol fermentation Figure 7.16a 2 ADP  2 P 2 ATP i Glucose Glycolysis 2 Pyruvate 2 NAD 2 NADH 2 CO2  2 H Figure 7.16a Fermentation (part 1: alcohol) 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 98

Muscle cells use lactic acid fermentation when O2 is scarce Lactic acid fermentation: pyruvate reduced by NADH, forming lactate (no release of CO2) Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Muscle cells use lactic acid fermentation when O2 is scarce © 2014 Pearson Education, Inc. 99

(b) Lactic acid fermentation Figure 7.16b 2 ADP  2 P 2 ATP i Glucose Glycolysis 2 NAD 2 NADH  2 H 2 Pyruvate Figure 7.16b Fermentation (part 2: lactic acid) 2 Lactate (b) Lactic acid fermentation 100

Comparing Fermentation with Anaerobic and Aerobic Respiration All use glycolysis (net ATP  2) All use NAD different final electron acceptors Cellular respiration …32 ATP per glucose; fermentation produces …2 ATP per glucose © 2014 Pearson Education, Inc. 101

Obligate anaerobes : only anaerobic …and cannot survive in O2 © 2014 Pearson Education, Inc. 102

facultative anaerobes: use either fermentation or cellular respiration

Ethanol, lactate, or other products Citric acid cycle Figure 7.17 Glucose Glycolysis CYTOSOL Pyruvate No O2 present: Fermentation O2 present: Aerobic cellular respiration MITOCHONDRION Ethanol, lactate, or other products Acetyl CoA Figure 7.17 Pyruvate as a key juncture in catabolism Citric acid cycle 104

The Evolutionary Significance of Glycolysis Ancient prokaryotes - thought to have used glycolysis before oxygen in atmosphere little O2 available until about 2.7 billion years ago, so early prokaryotes likely used glycolysis too © 2014 Pearson Education, Inc. 105

The Versatility of Catabolism Glycolysis accepts a wide range of carbohydrates Proteins digested to amino acids then amino groups removed before glycolysis or citric acid cycle © 2014 Pearson Education, Inc. 106

Fats digested to glycerol (used in glycolysis) and fatty acids Fatty acids broken down to acetyl CoA gram of fat produces more than 2X more ATP than a gram of carbohydrate © 2014 Pearson Education, Inc. 107

Amino acids Fatty acids Figure 7.18-1 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Figure 7.18-1 The catabolism of various molecules from food (step 1) 108

Amino acids Fatty acids Figure 7.18-2 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-2 The catabolism of various molecules from food (step 2) 109

Amino acids Fatty acids Figure 7.18-3 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-3 The catabolism of various molecules from food (step 3) Acetyl CoA 110

Amino acids Fatty acids Citric acid cycle Figure 7.18-4 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-4 The catabolism of various molecules from food (step 4) Acetyl CoA Citric acid cycle 111

Amino acids Fatty acids Citric acid cycle Oxidative phosphorylation Figure 7.18-5 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-5 The catabolism of various molecules from food (step 5) Acetyl CoA Citric acid cycle Oxidative phosphorylation 112