Cellular Respiration: Harvesting Chemical Energy Chapter 9 Cellular Respiration: Harvesting Chemical Energy

Living cells require energy from outside sources. Overview: Life Is Work Living cells require energy from outside sources. Some animals, such as the giant panda, obtain energy by eating plants, and some animals feed on other organisms that eat plants. For the Discovery Video Space Plants, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Energy flows into an ecosystem as sunlight and leaves as heat. Photosynthesis generates O2 and organic molecules C-H-O, which are used in cellular respiration. Cells use chemical energy stored in organic molecules C-H-O to regenerate ATP, which powers work. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Energy Flow and Chemical Recycling in Ecosystems ECOSYSTEM IN: Light Energy ECOSYSTEM Photosynthesis in chloroplasts Organic Molecules + O2 CO2 + H2O Cellular respiration in mitochondria Figure 9.2 ATP ATP powers most cellular work OUT: Heat energy

Catabolic pathways yield energy by oxidizing organic fuels: C-H-O molecules to Produce ATP The breakdown of organic molecules is exergonic. 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 without O2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Redox Reactions: Oxidation and Reduction Oxidation is a LOSS (of H or electrons). Reduction is a GAIN (of H or electrons). The transfer of electrons during chemical reactions releases energy stored in organic molecules. This released energy is ultimately used to synthesize ATP. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

In oxidation, a substance loses electrons, or is oxidized. 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). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Oxidation / Reduction Reactions becomes oxidized (loses electron) becomes reduced (gains electron)

Oxidation / Reduction Reactions becomes oxidized becomes reduced

The electron donor is oxidized and is called the reducing agent The electron receptor is reduced and is called the oxidizing agent Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds. An example is the reaction between methane and O2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Methane combustion as an energy-yielding redox reaction Reactants Products becomes oxidized becomes reduced Figure 9.3 Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water

Oxidation of Organic Fuel Molecules During Cellular Respiration The fuel C-H-O (such as glucose) is oxidized, looses H’s and O2 is reduced, gains H’s Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

During Cellular Respiration During cellular respiration, the fuel (such se) is oxidized, and O2 i becomes oxidized becomes reduced

NAD+ is Reduced to NADH + H+ Dehydrogenase

Stepwise Energy Harvest via NAD+ and the Electron Transport Chain In cellular respiration, glucose and other organic molecules are broken down in a series of steps. Electrons from organic compounds are usually first transferred to NAD+ = a coenzyme. As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration. NADH = the reduced form of NAD+ . Each NADH represents stored energy that is tapped to synthesize ATP. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

NAD+ as an electron shuttle 2 e– + 2 H+ 2 e– + H+ NADH H+ Dehydrogenase Reduction of NAD+ NAD+ + 2[H] + H+ Oxidation of NADH Nicotinamide (reduced form) Nicotinamide (oxidized form) Figure 9.4

NADH passes the electrons to the electron transport chain ETC. Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction. O2 pulls electrons down the ETC chain in an energy-yielding tumble. The energy yielded is used to regenerate ATP. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

An introduction to electron transport chains H2 + 1/2 O2 2 H + 1/2 O2 (from food C-H-O via NADH) Controlled release of energy for synthesis of ATP 2 H+ + 2 e– ATP Explosive release of heat and light energy ATP Electron transport chain Free energy, G Free energy, G ATP 2 e– Figure 9.5 1/2 O2 2 H+ H2O H2O (a) Uncontrolled reaction (b) Cellular respiration: step-wise controlled reaction

The Stages of Cellular Respiration: A Preview Cellular respiration has three stages: Glycolysis (breaks down glucose into two molecules of pyruvate) The citric acid cycle: Krebs Cycle (completes the breakdown of glucose) Oxidative phosphorylation (accounts for most of the ATP synthesis) by chemiosmosis. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

An overview of cellular respiration - Glycolysis Electrons carried via NADH Glycolysis Glucose Pyruvate Cytosol Figure 9.6 ATP Substrate-level phosphorylation

An overview of cellular respiration: Glycolysis & Krebs Cycle Electrons carried via NADH Electrons carried via NADH and FADH2 Glycolysis Krebs Cycle Glucose Pyruvate Mitochondrion Cytosol Figure 9.6 An overview of cellular respiration ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation

An overview of Cellular Respiration Basics Electrons carried via NADH Electrons carried via NADH and FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Krebs Cycle Glucose Pyruvate Mitochondrion Cytosol Figure 9.6 An overview of cellular respiration ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

The process in cell respiration that generates most of the ATP is oxidative phosphorylation (powered by redox reactions). Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration. A smaller amount of ATP is formed in glycolysis and the citric acid / Krebs Cycle by substrate-level phosphorylation. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Substrate-level phosphorylation Enzyme Enzyme ADP P Substrate + ATP Figure 9.7 Product

Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis (“sugar splitting”) breaks down glucose into two molecules of pyruvate. Glycolysis occurs in the cytoplasm and has two major phases: Energy investment phase = EA Energy payoff phase = ATP and NADH Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Energy investment phase The energy input and output of glycolysis 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 9.8 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+

A closer look at glycolysis Glucose-6-phosphate 2 Phosphogluco- ATP 1 Hexokinase ADP Glucose-6-phosphate Glucose-6-phosphate 2 Phosphoglucoisomerase 2 Phosphogluco- isomerase Fructose-6-phosphate Figure 9.9 Fructose-6-phosphate

Fructose- 1, 6-bisphosphate Glucose ATP 1 1 Hexokinase ADP Fructose-6-phosphate Glucose-6-phosphate 2 2 Phosphoglucoisomerase ATP 3 Phosphofructokinase: allosteric enzyme Fructose-6-phosphate ATP 3 3 ADP Phosphofructokinase ADP Figure 9.9 A closer look at glycolysis Fructose- 1, 6-bisphosphate Fructose- 1, 6-bisphosphate

Aldolase Isomerase Fructose- 1, 6-bisphosphate 4 5 Dihydroxyacetone Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate 2 Phosphoglucoisomerase Fructose- 1, 6-bisphosphate 4 Fructose-6-phosphate Aldolase ATP 3 Phosphofructokinase ADP Figure 9.9 A closer look at glycolysis 5 Isomerase Fructose- 1, 6-bisphosphate 4 Aldolase 5 Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate

2 2 ADP 2 ATP 2 3-Phosphoglycerate 1, 3-Bisphosphoglycerate 7 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 1, 3-Bisphosphoglycerate 2 ADP 2 3-Phosphoglycerate 7 Phosphoglycero- kinase 2 ATP Figure 9.9 A closer look at glycolysis 2 3-Phosphoglycerate

2 3-Phosphoglycerate 8 Phosphoglycero- mutase 2 2-Phosphoglycerate Fig. 9-9-7 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 3-Phosphoglycerate 2 3-Phosphoglycerate 8 Phosphoglyceromutase 8 Phosphoglycero- mutase 2 2-Phosphoglycerate Figure 9.9 A closer look at glycolysis 2 2-Phosphoglycerate

2 2-Phosphoglycerate Enolase 2 H2O 2 Phosphoenolpyruvate 9 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 2-Phosphoglycerate 2 3-Phosphoglycerate 8 Phosphoglyceromutase 9 Enolase 2 H2O 2 2-Phosphoglycerate 9 Enolase Figure 9.9 A closer look at glycolysis 2 H2O 2 Phosphoenolpyruvate 2 Phosphoenolpyruvate

Pyruvate 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 Phosphoenolpyruvate 2 ADP 2 3-Phosphoglycerate 8 10 Phosphoglyceromutase Pyruvate kinase 2 ATP 2 2-Phosphoglycerate 9 Enolase 2 H2O Figure 9.9 A closer look at glycolysis 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 Pyruvate 2 Pyruvate

If O2 is present, pyruvates (3 carbon C-H-O) enter the mitochondria. The Citric Acid Cycle = Krebs Cycle: completes the energy-yielding oxidation of organic molecules If O2 is present, pyruvates (3 carbon C-H-O) enter the mitochondria. Before the Krebs Cycle can begin, the pyruvate must be converted to acetyl CoA Acetyl CoA = Acetate + CoEnzyme A Acetate = a 2 carbon C-H-O CoEnzyme A = a carrier molecule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the citric acid cycle CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Acetyl CoA Figure 9.10 Pyruvate Coenzyme A CO2 Transport protein

The citric acid cycle / Krebs cycle takes place within the mitochondrial matrix. The Krebs cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn (two turns per glucose molecule from glycolysis). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

citric acid / Krebs Cycle Pyruvate CO2 NAD+ CoA NADH + H+ Acetyl CoA Figure 9.11 An overview of the FADH2 3 NAD+ FAD 3 NADH + 3 H+ ADP + P i ATP

The citric acid / Krebs cycle has eight steps, each catalyzed by a specific enzyme. The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, OAA, forming citrate (citric acid). The next seven steps break down the citrate and regenerate oxaloacetate,OAA, making the process a cycle. The NADH and FADH2 produced by the Krebs Cycle carry electrons extracted from food (C-H-O) to the electron transport chain in the mitochondrial cristae membrane. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

A closer look at the citric acid / Krebs cycle Citric Acid Cycle Acetyl CoA CoA—SH NADH +H+ 1 H2O NAD+ 8 Oxaloacetate OAA 2 Malate Citrate Isocitrate NAD+ Citric Acid Cycle NADH 3 + H+ 7 H2O CO2 Fumarate CoA—SH -Keto- glutarate Figure 9.12 4 6 CoA—SH FADH2 5 CO2 NAD+ FAD Succinate P NADH i GTP GDP Succinyl CoA + H+ ADP ATP

During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food. These two electron carriers: NADH and FADH2 donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation. For the Cell Biology Video ATP Synthase 3D Structure — Side View, go to Animation and Video Files. For the Cell Biology Video ATP Synthase 3D Structure — Top View, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Pathway of Electron Transport The electron transport chain is in the cristae membrane of the mitochondrion. 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, redox. Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O (waste). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

ETC cristae Free-energy change during electron transport waste NADH 50 2 e– NAD+ FADH2 2 e– FAD Multiprotein complexes  40 FMN FAD Fe•S  Fe•S Q  Cyt b Fe•S 30 Cyt c1 IV Free energy (G) relative to O2 (kcal/mol) Cyt c Cyt a Cyt a3 20 Figure 9.13 2 e– 10 (from NADH or FADH2) 2 H+ + 1/2 O2 waste H2O

The electron transport chain generates no ATP Electrons are transferred from NADH or FADH2 to the electron transport chain, ETC. Electrons are passed along the cristae membrane through a number of proteins including cytochromes (each with an iron atom) to O2 The electron transport chain generates no ATP The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chemiosmosis The Energy-Coupling Mechanism Electron transfer, redox, in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space  creating a proton H+ gradient. H+ then moves back across the membrane, passing through channels in 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 ATP synthesis. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chemiosomosis The energy stored in a H+ (proton) gradient, across a membrane couples the redox reactions of the electron transport chain to ATP synthesis. The H+ gradient is a proton-motive force, emphasizing its capacity to do work. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Chemiosmosis: Energy Coupling - couples the electron transport chain to ATP synthesis Protein complex of electron carriers Cyt c V Q   ATP synthase  2 H+ + 1/2O2 H2O FADH2 FAD NADH NAD+ Figure 9.16 Chemiosmosis ADP + P ATP i (carrying electrons from food) H+ 1 Electron transport chain: redox 2 Chemiosmosis Oxidative phosphorylation

An Accounting of ATP Production by Cellular Respiration During cellular respiration, most energy flows in this sequence: glucose  NADH  electron transport chain  proton-motive force  ATP About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Aerobic Cellular Respiration ATP yield per molecule of glucose at each stage of cellular respiration CYTOSOL Electron shuttles span membrane MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Citric Acid Cycle Oxidative phosphorylation: electron transport chemiosmosis Glycolysis 2 Pyruvate 2 Acetyl CoA Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP Figure 9.17 About 36 or 38 ATP Maximum per glucose:

Most cellular respiration requires O2 to produce ATP. Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Most cellular respiration requires O2 to produce ATP. Glycolysis produces ATP without O2 (in aerobic or anaerobic conditions). In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fermentation: Anaerobic / No Oxygen Used Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis. Two common types are alcohol fermentation and lactic acid fermentation. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 Alcohol fermentation by yeast is used in brewing, winemaking, and baking / $$ commercial uses. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fermentation Regenerates NAD+ for use in Glycolysis 2 ADP + 2 Pi 2 ATP Glucose Glycolysis 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation 2 ADP + 2 Pi 2 ATP Glucose Glycolysis Figure 9.18 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate 2 Lactate (b) Lactic acid fermentation

In lactic acid fermentation, pyruvate is reduced to 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; meaning there is an O2 debt. This reaction is reversible when O2 is available. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Lactic acid fermentation: reversible if oxygen is available 2 ADP + 2 P 2 ATP i Glucose Glycolysis 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate Figure 9.18b Fermentation 2 Lactate Lactic acid fermentation: reversible if oxygen is available

Fermentation and Aerobic Respiration Compared Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation. O2 in aerobic cellular respiration. Aerobic cellular respiration nets 38 ATP per glucose molecule; fermentation nets only 2 ATP per glucose molecule. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Micro-organisms Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2 Facultative anaerobes (yeast and many bacteria) 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. Obligate aerobes carry out aerobic cellular respiration and require O2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

O2 present: No O2 present: Pyruvate as a key juncture in catabolism Glucose Glycolysis CYTOSOL Pyruvate O2 present: Aerobic cellular respiration No O2 present: Fermentation MITOCHONDRION Ethanol or lactate Acetyl CoA Figure 9.19 Citric acid cycle

The Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms. Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere. Fermentation evolved to recycle NAD+ back to glycolysis so ATP production continues in the absence of O2 Gycolysis and the Citric Acid Cycle are major intersections to various catabolic and anabolic pathways. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Versatility of Catabolism: breaking down Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration. Glycolysis accepts a wide range of carbohydrates. Proteins must be digested to amino acids which can feed glycolysis or the citric acid cycle. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fatty acids are broken down by beta oxidation and yield acetyl CoA. Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA). Fatty acids are broken down by beta oxidation and yield acetyl CoA. An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate (fat has more calories = unit of energy for cell work). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Versatility Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Figure 9.20 The catabolism of various molecules from food Citric acid cycle Oxidative phosphorylation

Biosynthesis - Anabolic Pathways: Building The body uses small molecules to build larger more complex molecules. These small molecules may come directly from food, from glycolysis, or from the citric acid cycle. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Regulation of Cellular Respiration via Feedback Mechanisms Feedback inhibition is the most common mechanism for control, regulation. If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down. Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Regulation: Feedback Inhibition The control of cellular respiration Glucose AMP Glycolysis Fructose-6-phosphate Stimulates + Phosphofructokinase – – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Figure 9.21 Citric acid cycle Oxidative phosphorylation

Review Glycolysis: Inputs Outputs 2 ATP Glycolysis + 2 NADH Glucose 2 Pyruvate

Review: Citric Acid / Krebs Cycle Inputs Outputs S—CoA 2 ATP C O CH3 2 Acetyl CoA 6 NADH O C COO Citric acid cycle CH2 2 FADH2 COO 2 Oxaloacetate

Chemiosmosis = ATP Synthesis Review: Energy Coupling: INTER- MEMBRANE SPACE H+ ATP synthase ADP + P ATP i MITO- CHONDRIAL MATRIX H+

Proton Motive Force = H+ concentration Gradient Proton Motive Force = H+ concentration Gradient. As H’s increase, the pH drops in the Intermembrane space; so pH difference Increases across the membrane

You should now be able to: Explain in general terms how redox reactions are involved in energy exchanges. Name the three stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result. In general terms, explain the role of the electron transport chain in cellular respiration. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Distinguish between fermentation and anaerobic respiration. Explain where and how the respiratory electron transport chain creates a proton gradient. Distinguish between fermentation and anaerobic respiration. Distinguish between obligate and facultative anaerobes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings