9 Cellular Respiration and Fermentation

Overview: Life Is Work Living cells require energy from outside sources Some animals, such as the giraffe, obtain energy by eating plants, and some animals feed on other organisms that eat plants © 2014 Pearson Education, Inc. 2

Learning Outcomes I can characterize oxidation/reduction reactions in biological systems.

Concept 1: Catabolic pathways yield energy by oxidizing organic fuels Several processes are central to cellular respiration and related pathways The breakdown of organic molecules is exergonic TERMS Fermentation is a partial degradation of sugars that occurs without O2 Aerobic respiration consumes organic molecules and O2 and yields ATP Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2 Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration 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  heat) Nicotinamide Adenine Dinucleotide - (NAD) - Coenzyme that functions as a carrier of electrons, especially in aerobic cellular respiration. © 2014 Pearson Education, Inc. 4

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 ATP 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) 5

Reactants Products becomes oxidized becomes reduced Methane (reducing Figure 7.3 Reactants Products becomes oxidized becomes reduced Figure 7.3 Methane combustion as an energy-yielding redox reaction Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water 6

Oxidation of Organic Fuel Molecules During Cellular Respiration During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced Organic molecules with an abundance of hydrogen, like carbohydrates and fats, are excellent fuels As hydrogen (with its electron) is transferred to oxygen, energy is released that can be used in ATP synthesis © 2014 Pearson Education, Inc. 7

Learning Outcomes I will calculate the energy yield from glycolysis I will distinguish between aerobic and anaerobic respiration

2 Types of Cell Respiration: Anaerobic &Aerobic Without oxygen present: Glycolysis (breaks down glucose into two molecules of pyruvate) Followed by either alcoholic fermentation or lactic acid With oxygen present: Glycolysis (breaks down glucose into two molecules of pyruvate)… Pyruvate oxidation and the Citric Acid Cycle or Kreb’s Cycle (completes the breakdown of glucose)…. Oxidative phosphorylation (accounts for most of the ATP synthesis)…THE END?? Electron Transport Chain (ETC) Chemosmosis 9

Overview of ATP Production 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: 10

Concept 2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis occurs whether or not O2 is present Breaks downs 1 molecule of glucose into pyruvate and releases 4 ATP BUT net gain of 2 ATP!! Occurs in cytoplasm and has 2 major phases: investment and payoff Pyruvate is the critical end product needed for Krebs Cycle ATP is produced by substrate level phosphorylation (PFK) phosphofructokinase is an allosteric enzyme which inhibits glycolysis when there is enough ATP available Tutorial 6.2 Allosteric Regulation of Enzymesl What is the inhibitor? ATP Animation: Big Picture Glycolysis Animation © 2014 Pearson Education, Inc. 11

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 12

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: 13

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 14

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 15

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) 16

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) 17

Learning Outcomes I will describe the segments and reactions of the Krebs cycle I will explain the fate of the electrons produced by the Krebs cycle

Concept 3: After pyruvate is oxidized, the citric acid cycle (Kreb’s Cycle) completes the energy-yielding oxidation of organic molecules Cyclical series of enzyme-catalyzed reactions Occurs in the mitochondria matrix and requires pyruvate In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells), where the oxidation of glucose is completed Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links glycolysis to the citric acid cycle The cycle oxidizes organic fuel derived from pyruvate generating: 1 ATP, 3 NADH, 1 FADH2 and the waste product CO2 per turn Concept 3 Review: Krebs Cycle ADVANCED Animation: How the Krebs Cycle Works © 2014 Pearson Education, Inc. 19

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 20

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 21

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 22

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) 23

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) 24

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 25

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 26

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 27

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 28

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 29

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 30

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 31

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 32

Learning Outcomes I will describe the structure and function of the electron transport chain I will explain how the proton gradient connects electron transport with ATP synthesis

Concept 4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis ETC carriers electrons delivered by NAD and FAD from glycolysis and Kreb’s Cycle to oxygen (final electron/hydrogen acceptor) via series of redox reactions. The highly electronegative oxygen acts to pull electrons through ETC NADH delivers its electrons to higher level than FADH2 – as a result NADH produces 3 ATP while FADH2 produces 2 ATP ETC consist mostly cytochromes which are structural proteins present in ALL aerobes and used to trace evolutionary relationships. Animation: How the NAD+ Works © 2014 Pearson Education, Inc. 34

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 35

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 36

Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in the electron transport chain causes proteins to pump H from the mitochondrial matrix to the intermembrane space H then moves back across the membrane, passing through the protein complex, ATP synthase ATP synthase uses the exergonic flow of H to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H gradient to drive cellular work © 2014 Pearson Education, Inc. 37

ETC and Chemiosmosis ANIMATION 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 ETC and Chemiosmosis ANIMATION 38

Summary of ATP Production ATP is produced in 2 ways: Substrate level phosphorylation – transfers a phosphate from a substrate directly to ADP. Very little ATP produced is formed in glycolysis and the citric acid cycle Oxidative Phosphorylation – occurs during chemiosmosis, makes up to 90% of the ATP produced and it is powered by redox reactions For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP © 2014 Pearson Education, Inc. 39

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 32ATP About 36ATP Maximum per glucose: 40

Learning Outcomes I will calculate the number of ATP molecules produced by anaerobic respiration

Concept 5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Two common types are alcohol fermentation and lactic acid fermentation In alcohol fermentation, pyruvate is converted to ethanol in two steps The first step releases CO2 from pyruvate, and the second step reduces acetaldehyde to ethyl alcohol Alcohol fermentation by yeast is used in brewing, winemaking, and baking In lactic acid fermentation, pyruvate is reduced by 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 Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule Fermentation Animation © 2014 Pearson Education, Inc. 42

(a) Alcohol fermentation (b) Lactic acid fermentation Figure 7.16 2 ADP  2 P 2 ADP  2 i 2 ATP P i 2 ATP Glucose Glycolysis Glucose Glycolysis 2 Pyruvate 2 NAD 2 NADH 2 CO2 2 NAD 2 NADH  2 H  2 H 2 Pyruvate Figure 7.16 Fermentation 2 Ethanol 2 Acetaldehyde 2 Lactate (a) Alcohol fermentation (b) Lactic acid fermentation 43

Concept 6: The Evolutionary Significance of Glycolysis Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP Glycolysis is a very ancient process © 2014 Pearson Education, Inc. 45

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