Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 9 Cellular Respiration: Harvesting Chemical Energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Life Is Work Living cells – Require transfusions of energy from outside sources to perform their many tasks

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The giant panda – Obtains energy for its cells by eating plants Figure 9.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy – Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Heat energy Figure 9.2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Catabolic Pathways and Production of ATP The breakdown of organic molecules is exergonic

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings One catabolic process, fermentation – Is a partial degradation of sugars that occurs without oxygen

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular respiration – Is the most prevalent and efficient catabolic pathway – Consumes oxygen and organic molecules such as glucose – Yields ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings To keep working – Cells must regenerate ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox Reactions: Oxidation and Reduction Catabolic pathways yield energy – Due to the transfer of electrons

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Principle of Redox Redox reactions – Transfer electrons from one reactant to another by oxidation and reduction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In oxidation – A substance loses electrons, or is oxidized In reduction – A substance gains electrons, or is reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Examples of redox reactions Na + Cl Na + + Cl – becomes oxidized (loses electron) becomes reduced (gains electron)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some redox reactions – Do not completely exchange electrons – Change the degree of electron sharing in covalent bonds CH 4 H H H H C OO O O O C HH Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxideWater + 2O 2 CO 2 + Energy + 2 H 2 O becomes oxidized becomes reduced Reactants Products Figure 9.3

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidation of Organic Fuel Molecules During Cellular Respiration During cellular respiration – Glucose is oxidized and oxygen is reduced C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest via NAD + and the Electron Transport Chain Cellular respiration – Oxidizes glucose in a series of steps

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electrons from organic compounds – Are usually first transferred to NAD +, a coenzyme NAD + H O O OO–O– O O O–O– O O O P P CH 2 HO OH H H HOOH HO H H N+N+ C NH 2 H N H N N Nicotinamide (oxidized form) NH 2 + 2[H] (from food) Dehydrogenase Reduction of NAD + Oxidation of NADH 2 e – + 2 H + 2 e – + H + NADH O H H N C + Nicotinamide (reduced form) N Figure 9.4

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NADH, the reduced form of NAD + – Passes the electrons to the electron transport chain

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If electron transfer is not stepwise – A large release of energy occurs – As in the reaction of hydrogen and oxygen to form water (a) Uncontrolled reaction Free energy, G H2OH2O Explosive release of heat and light energy Figure 9.5 A H / 2 O 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The electron transport chain – Passes electrons in a series of steps instead of in one explosive reaction – Uses the energy from the electron transfer to form ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 H 1 / 2 O 2 (from food via NADH) 2 H e – 2 H + 2 e – H2OH2O 1 / 2 O 2 Controlled release of energy for synthesis of ATP ATP Electron transport chain Free energy, G (b) Cellular respiration + Figure 9.5 B

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Stages of Cellular Respiration: A Preview Respiration is a cumulative function of three metabolic stages – Glycolysis – The citric acid cycle – Oxidative phosphorylation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis – Breaks down glucose into two molecules of pyruvate The citric acid cycle – Completes the breakdown of glucose

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative phosphorylation – Is driven by the electron transport chain – Generates ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH 2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion Cytosol

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Both glycolysis and the citric acid cycle – Can generate ATP by substrate-level phosphorylation Figure 9.7 Enzyme ATP ADP Product Substrate P +

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate Glycolysis – Means “splitting of sugar” – Breaks down glucose into pyruvate – Occurs in the cytoplasm of the cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis consists of two major phases – Energy investment phase – Energy payoff phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 P 2 NAD e H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2 NAD e – + 4 H + 2 NADH + 2 H + Figure 9.8

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the energy investment phase

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H H H H H OH HO CH 2 OH H H H H O H OH HO OH P CH 2 O P H O H HO H CH 2 OH P O CH 2 O O P HO H H OH O P CH 2 C O CH 2 OH H C CHOH CH 2 O O P ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate ATP ADP Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Glycolysis CH 2 OH Oxidative phosphorylation Citric acid cycle Figure 9.9 A

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the energy payoff phase

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 NAD + NADH H + Triose phosphate dehydrogenase 2 P i 2 P C CHOH O P O CH 2 O 2 O–O– 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase CH 2 OP 2 C CHOH 3-Phosphoglycerate Phosphoglyceromutase O–O– C C CH 2 OH H O P 2-Phosphoglycerate 2 H 2 O 2 O–O– Enolase C C O P O CH 2 Phosphoenolpyruvate 2 ADP 2 ATP Pyruvate kinase O–O– C C O O CH Pyruvate O Figure 9.8 B

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules The citric acid cycle – Takes place in the matrix of the mitochondrion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Before the citric acid cycle can begin – Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis CYTOSOLMITOCHONDRION NADH + H + NAD CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of the citric acid cycle ATP 2 CO 2 3 NAD + 3 NADH + 3 H + ADP + P i FAD FADH 2 Citric acid cycle CoA Acetyle CoA NADH + 3 H + CoA CO 2 Pyruvate (from glycolysis, 2 molecules per glucose) ATP Glycolysis Citric acid cycle Oxidative phosphorylatio n Figure 9.11

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the citric acid cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.12 Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA  -Ketoglutarate Isocitrate Citric acid cycle SCoA SH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CoA SH CoA SH CoA S H2OH2O + H + H2OH2O C CH 3 O OCCOO – CH 2 COO – CH 2 HO C COO – CH 2 COO – CH 2 HCCOO – HOCH COO – CH CH 2 COO – HO COO – CH HC COO – CH 2 COO – CH 2 CO COO – CH 2 CO COO – Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis NADH and FADH 2 – Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Pathway of Electron Transport In the electron transport chain – Electrons from NADH and FADH 2 lose energy in several steps

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At the end of the chain – Electrons are passed to oxygen, forming water H2OH2O O2O2 NADH FADH2 FMN FeS O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H  2 I II III IV Multiprotein complexes Free energy (G) relative to O 2 (kcl/mol) Figure 9.13

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis: The Energy-Coupling Mechanism ATP synthase – Is the enzyme that actually makes ATP INTERMEMBRANE SPACE H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ P i + ADP ATP A rotor within the membrane spins clockwise when H + flows past it down the H + gradient. A stator anchored in the membrane holds the knob stationary. A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP. MITOCHONDRIAL MATRIX Figure 9.14

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At certain steps along the electron transport chain – Electron transfer causes protein complexes to pump H + from the mitochondrial matrix to the intermembrane space

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The resulting H + gradient – Stores energy – Drives chemiosmosis in ATP synthase – Is referred to as a proton-motive force

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis – Is an energy-coupling mechanism that uses energy in the form of a H + gradient across a membrane to drive cellular work

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis and the electron transport chain Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+H+ H+H+ H+H+ H+H+ H+H+ ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H / 2 O 2 H2OH2O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An Accounting of ATP Production by Cellular Respiration During respiration, most energy flows in this sequence – Glucose to NADH to electron transport chain to proton-motive force to ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There are three main processes in this metabolic enterprise Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH 2 2 NADH 6 NADH 2 FADH 2 2 NADH Glycolysis Glucose 2 Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Maximum per glucose: About 36 or 38 ATP + 2 ATP + about 32 or 34 ATP or Figure 9.16

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings About 40% of the energy in a glucose molecule – Is transferred to ATP during cellular respiration, making approximately 38 ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen Cellular respiration – Relies on oxygen to produce ATP In the absence of oxygen – Cells can still produce ATP through fermentation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis – Can produce ATP with or without oxygen, in aerobic or anaerobic conditions – Couples with fermentation to produce ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Fermentation Fermentation consists of – Glycolysis plus reactions that regenerate NAD +, which can be reused by glyocolysis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In alcohol fermentation – Pyruvate is converted to ethanol in two steps, one of which releases CO 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings During lactic acid fermentation – Pyruvate is reduced directly to NADH to form lactate as a waste product

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 ADP + 2 P1P1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 P1P1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Lactate (b) Lactic acid fermentation H H OH CH 3 C O – O C CO CH 3 H CO O–O– CO CO O CO C OHH CH 3 CO 2 2 Figure 9.17

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation and Cellular Respiration Compared Both fermentation and cellular respiration – Use glycolysis to oxidize glucose and other organic fuels to pyruvate

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation and cellular respiration – Differ in their final electron acceptor Cellular respiration – Produces more ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvate is a key juncture in catabolism Glucose CYTOSOL Pyruvate No O 2 present Fermentation O 2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Evolutionary Significance of Glycolysis Glycolysis – Occurs in nearly all organisms – Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Versatility of Catabolism Catabolic pathways – Funnel electrons from many kinds of organic molecules into cellular respiration

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The catabolism of various molecules from food Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH 3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Biosynthesis (Anabolic Pathways) The body – Uses small molecules to build other substances These small molecules – May come directly from food or through glycolysis or the citric acid cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Cellular Respiration via Feedback Mechanisms Cellular respiration – Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The control of cellular respiration Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + – – Figure 9.20