Chapter 9 Cellular Respiration Harvesting Chemical Energy Power

Chapter 9 Cellular Respiration: Harvesting Chemical Energy Power. Point® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

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

Fig. 9 -1

• Energy flows into an ecosystem as sunlight and leaves as heat • Photosynthesis generates O 2 and organic molecules, which are used in cellular respiration • Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2 O Organic +O molecules 2 Cellular respiration in mitochondria ATP powers most cellular work Heat energy

Concept 9. 1: Catabolic pathways yield energy by oxidizing organic fuels • Several processes are central to cellular respiration and related pathways Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Catabolic Pathways and Production of ATP • The breakdown of organic molecules is exergonic • Fermentation is a partial degradation of sugars that occurs without O 2 • Aerobic respiration consumes organic molecules and O 2 and yields ATP • Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O 2 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: C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + Energy (ATP + heat) Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

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

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

Fig. 9 -UN 1 becomes oxidized (loses electron) becomes reduced (gains electron)

Fig. 9 -UN 2 becomes oxidized becomes reduced

• The electron donor is called the reducing agent • The electron receptor 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 O 2 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -3 Reactants Products becomes oxidized becomes reduced Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water

Oxidation of Organic Fuel Molecules During Cellular Respiration • During cellular respiration, the fuel (such as glucose) is oxidized, and O 2 is reduced: Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -UN 3 becomes oxidized becomes reduced

Fig. 9 -UN 4 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 • Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -4 2 e– + 2 H+ 2 e– + H+ NADH H+ Dehydrogenase NAD+ + 2[H] Reduction of NAD+ + H+ Oxidation of NADH Nicotinamide (reduced form) Nicotinamide (oxidized form)

• NADH passes the electrons to the electron transport chain • Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction • O 2 pulls electrons down the chain in an energyyielding tumble • The energy yielded is used to regenerate ATP Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -5 ort Free energy, G Explosive release of heat and light energy + 2 H (from food via NADH) Controlled release of + – 2 H + 2 e energy for synthesis of ATP sp tran tron Elec chain Free energy, G H 2 + 1 / 2 O 2 ATP 2 e– 2 1/ H+ H 2 O (a) Uncontrolled reaction 1/ H 2 O (b) Cellular respiration 2 O 2

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 (completes the breakdown of glucose) – Oxidative phosphorylation (accounts for most of the ATP synthesis) Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -6 -1 Electrons carried via NADH Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation

Fig. 9 -6 -2 Electrons carried via NADH and FADH 2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Mitochondrion Cytosol ATP Substrate-level phosphorylation

Fig. 9 -6 -3 Electrons carried via NADH and FADH 2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion Cytosol ATP ATP Substrate-level phosphorylation Oxidative phosphorylation

• The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions Bio. Flix: Cellular Respiration Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

• 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 cycle by substrate -level phosphorylation Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -7 Enzyme ADP P Substrate + Product ATP

Concept 9. 2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate • Glycolysis occurs in the cytoplasm and has two major phases: – Energy investment phase – Energy payoff phase Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -8 Energy investment phase Glucose 2 ADP + 2 P 2 ATP used 4 ATP formed Energy payoff phase 4 ADP + 4 P 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ 2 Pyruvate + 2 H 2 O Net Glucose 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H+ 2 Pyruvate + 2 H 2 O 2 ATP 2 NADH + 2 H+

Fig. 9 -9 -1 Glucose ATP 1 Hexokinase ADP Glucose-6 -phosphate

Fig. 9 -9 -2 Glucose ATP 1 Hexokinase ADP Glucose-6 -phosphate 2 Phosphoglucoisomerase Fructose-6 -phosphate

Fig. 9 -9 -3 Glucose ATP 1 Hexokinase AD P Fructose-6 -phosphate Glucose-6 -phosphate 2 Phosphoglucoisomerase ATP 3 Phosphofructokinase Fructose-6 -phosphate ATP 3 Phosphofructokinase ADP AD P Fructose 1, 6 -bisphosphate

Fig. 9 -9 -4 Glucose ATP 1 Hexokinase AD P Glucose-6 -phosphate 2 Phosphoglucoisomerase Fructose 1, 6 -bisphosphate 4 Fructose-6 -phosphate ATP Aldolase 3 Phosphofructokinase AD P 5 Isomerase Fructose 1, 6 -bisphosphate 4 Aldolase 5 Isomerase Dihydroxyacetone phosphate Glyceraldehyde 3 -phosphate

Fig. 9 -9 -5 2 NAD+ 2 NADH + 2 H+ 6 Triose phosphate dehydrogenase 2 Pi 2 1, 3 -Bisphoglycerate Glyceraldehyde 3 -phosphate 2 NAD+ 2 NADH 6 Triose phosphate dehydrogenase 2 Pi + 2 H+ 2 1, 3 -Bisphoglycerate

Fig. 9 -9 -6 2 NAD+ 2 NADH + 2 H+ 6 Triose phosphate dehydrogenase 2 Pi 2 1, 3 -Bisphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 1, 3 -Bisphoglycerate 2 ADP 2 3 -Phosphoglycerate 2 ATP 2 7 Phosphoglycerokinase 3 -Phosphoglycerate

Fig. 9 -9 -7 2 NAD+ 2 NADH + 2 H+ 6 Triose phosphate dehydrogenase 2 Pi 2 1, 3 -Bisphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 3 -Phosphoglycerate 8 2 3 -Phosphoglycerate Phosphoglyceromutase 2 8 Phosphoglyceromutase 2 -Phosphoglycerate 2 2 -Phosphoglycerate

Fig. 9 -9 -8 2 NAD+ 2 NADH + 2 H+ 6 Triose phosphate dehydrogenase 2 Pi 2 1, 3 -Bisphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 3 -Phosphoglycerate 2 2 -Phosphoglycerate 8 Phosphoglyceromutase 2 9 2 H 2 O 2 -Phosphoglycerate Enolase 9 2 H 2 O 2 Enolase Phosphoenolpyruvate 2 Phosphoenolpyruvate

Fig. 9 -9 -9 2 NAD+ 2 NADH + 2 H+ 6 Triose phosphate dehydrogenase 2 Pi 2 1, 3 -Bisphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 Phosphoenolpyruvate 2 ADP 2 3 -Phosphoglycerate 8 10 Pyruvate kinase Phosphoglyceromutase 2 ATP 2 2 -Phosphoglycerate 9 2 H 2 O Enolase 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 2 Pyruvate

Concept 9. 3: The citric acid cycle completes the energy-yielding oxidation of organic molecules • In the presence of O 2, pyruvate enters the mitochondrion • Before the citric acid cycle can begin, pyruvate must be converted to acetyl Co. A, which links the cycle to glycolysis Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -10 CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 Pyruvate Transport protein 3 CO 2 Coenzyme A Acetyl Co. A

• The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix • The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH 2 per turn Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -11 Pyruvate CO 2 NAD+ Co. A NADH + H+ Acetyl Co. A Citric acid cycle FADH 2 2 CO 2 3 NAD+ 3 NADH FAD + 3 H+ ADP + P i ATP

• The citric acid cycle has eight steps, each catalyzed by a specific enzyme • The acetyl group of acetyl Co. A joins the cycle by combining with oxaloacetate, forming citrate • The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle • The NADH and FADH 2 produced by the cycle relay electrons extracted from food to the electron transport chain Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -12 -1 Acetyl Co. A—SH 1 Oxaloacetate Citric acid cycle

Fig. 9 -12 -2 Acetyl Co. A—SH H 2 O 1 Oxaloacetate 2 Citrate Isocitrate Citric acid cycle

Fig. 9 -12 -3 Acetyl Co. A—SH 1 H 2 O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle 3 NADH + H+ CO 2 -Ketoglutarate

Fig. 9 -12 -4 Acetyl Co. A—SH 1 H 2 O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle NADH + H+ 3 CO 2 Co. A—SH -Ketoglutarate 4 NAD+ Succinyl Co. A NADH + H+ CO 2

Fig. 9 -12 -5 Acetyl Co. A—SH 1 H 2 O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle NADH + H+ 3 CO 2 Co. A—SH -Ketoglutarate 4 Co. A—SH 5 NAD+ Succinate GTP GDP ATP Pi Succinyl Co. A NADH + H+ CO 2

Fig. 9 -12 -6 Acetyl Co. A—SH H 2 O 1 Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle Fumarate NADH + H+ 3 CO 2 Co. A—SH 6 -Ketoglutarate 4 Co. A—SH 5 FADH 2 NAD+ FAD Succinate GTP GDP ATP Pi Succinyl Co. A NADH + H+ CO 2

Fig. 9 -12 -7 Acetyl Co. A—SH H 2 O 1 Oxaloacetate 2 Malate Citrate Isocitrate NAD+ H 2 O Citric acid cycle 7 Fumarate NADH + H+ 3 CO 2 Co. A—SH 6 -Ketoglutarate 4 Co. A—SH 5 FADH 2 NAD+ FAD Succinate GTP GDP ATP Pi Succinyl Co. A NADH + H+ CO 2

Fig. 9 -12 -8 Acetyl Co. A—SH NADH +H+ H 2 O 1 NAD+ 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD+ H 2 O Citric acid cycle 7 Fumarate NADH + H+ 3 CO 2 Co. A—SH 6 -Ketoglutarate 4 Co. A—SH 5 FADH 2 NAD+ FAD Succinate GTP GDP ATP Pi Succinyl Co. A NADH + H+ CO 2

Concept 9. 4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP 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 ATP synthesis via oxidative phosphorylation Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

The Pathway of Electron Transport • The electron transport chain is in the cristae 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 • Electrons drop in free energy as they go down the chain and are finally passed to O 2, forming H 2 O Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -13 NADH 50 2 e– NAD+ FADH 2 2 e– Free energy (G) relative to O 2 (kcal/mol) 40 FMN FAD Multiprotein complexes FAD Fe • S Q Cyt b 30 Fe • S Cyt c 1 IV Cyt c Cyt a 20 10 0 Cyt a 3 2 e– (from NADH or FADH 2) 2 H+ + 1/2 O 2 H 2 O

• 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 ATP • The chain’s function is to break the large freeenergy drop from food to O 2 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 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 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 cellular work Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -14 INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Catalytic knob ADP + P i ATP MITOCHONDRIAL MATRIX

EXPERIMENT Magnetic bead Electromagnet Sample Internal rod Catalytic knob Nickel plate RESULTS Rotation in one direction Rotation in opposite direction Number of photons detected ( 103) Fig. 9 -15 No rotation 30 25 20 0 Sequential trials

Fig. 9 -15 a EXPERIMENT Magnetic bead Electromagnet Sample Internal rod Catalytic knob Nickel plate

Fig. 9 -15 b Number of photons detected (x 103) RESULTS Rotation in one direction Rotation in opposite direction No rotation 30 25 20 0 Sequential trials

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

Fig. 9 -16 H+ H+ H+ Protein complex of electron carriers H+ Cyt c V Q FADH 2 NADH ATP synthase FAD 2 H+ + 1/2 O 2 NAD+ H 2 O ADP + P i (carrying electrons from food) ATP H+ 1 Electron transport chain Oxidative phosphorylation 2 Chemiosmosis

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

Fig. 9 -17 Electron shuttles span membrane CYTOSOL 2 NADH Glycolysis Glucose 2 Pyruvate MITOCHONDRION 2 NADH or 2 FADH 2 6 NADH 2 Acetyl Co. A + 2 ATP Citric acid cycle + 2 ATP Maximum per glucose: About 36 or 38 ATP 2 FADH 2 Oxidative phosphorylation: electron transport and chemiosmosis + about 32 or 34 ATP

Concept 9. 5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen • Most cellular respiration requires O 2 to produce ATP • Glycolysis can produce ATP with or without O 2 (in aerobic or anaerobic conditions) • In the absence of O 2, glycolysis couples with fermentation or anaerobic respiration to produce ATP Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

• Anaerobic respiration uses an electron transport chain with an electron acceptor other than O 2, for example sulfate • Fermentation uses phosphorylation instead of an electron transport chain to generate ATP Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Types of Fermentation • 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 CO 2 • Alcohol fermentation by yeast is used in brewing, winemaking, and baking Fermentation Overview Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -18 2 ADP + 2 Pi Glucose 2 ATP Glycolysis 2 Pyruvate 2 NAD+ 2 NADH + 2 H+ 2 CO 2 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 Pi Glucose 2 ATP Glycolysis 2 NAD+ 2 Lactate (b) Lactic acid fermentation 2 NADH + 2 H+ 2 Pyruvate

Fig. 9 -18 a 2 ADP + 2 P i Glucose 2 ATP Glycolysis 2 Pyruvate 2 NAD+ 2 Ethanol (a) Alcohol fermentation 2 NADH + 2 H+ 2 CO 2 2 Acetaldehyde

• In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO 2 • 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 O 2 is scarce Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -18 b 2 ADP + 2 P i Glucose 2 ATP Glycolysis 2 NAD+ 2 Lactate (b) Lactic acid fermentation 2 NADH + 2 H+ 2 Pyruvate

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 and O 2 in cellular respiration • Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

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

Fig. 9 -19 Glucose CYTOSOL Glycolysis Pyruvate No O 2 present: Fermentation O 2 present: Aerobic cellular respiration MITOCHONDRION Ethanol or lactate Acetyl Co. A 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 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

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

The Versatility of Catabolism • 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; amino groups can feed glycolysis or the citric acid cycle Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

• Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl Co. A) • Fatty acids are broken down by beta oxidation and yield acetyl Co. A • An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 9 -20 Proteins Amino acids Carbohydrates Sugars Glycolysis Glucose Glyceraldehyde-3 - P NH 3 Pyruvate Acetyl Co. A Citric acid cycle 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, 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 • 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

Fig. 9 -21 Glucose Glycolysis Fructose-6 -phosphate – AMP Stimulates + Phosphofructokinase – Fructose-1, 6 -bisphosphate Inhibits Pyruvate ATP Citrate Acetyl Co. A Citric acid cycle Oxidative phosphorylation

Fig. 9 -UN 5 Outputs Inputs 2 Glycolysis ATP + 2 NADH Glucose 2 Pyruvate

Fig. 9 -UN 6 Inputs Outputs S—Co. A C 2 ATP O CH 3 2 Acetyl Co. A 6 NADH O C COO CH 2 COO 2 Oxaloacetate Citric acid cycle 2 FADH 2

Fig. 9 -UN 7 INTERMEMBRANE SPACE H+ ATP synthase ADP + P i MITOCHONDRIAL MATRIX ATP H+

p. H difference across membrane Fig. 9 -UN 8 Time

Fig. 9 -UN 9

You should now be able to: 1. Explain in general terms how redox reactions are involved in energy exchanges 2. Name three stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result 3. In general terms, explain the role of the electron transport chain in cellular respiration Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

4. Explain where and how the respiratory electron transport chain creates a proton gradient 5. Distinguish between fermentation and anaerobic respiration 6. Distinguish between obligate and facultative anaerobes Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings