Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.1 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 Redox Reactions: Oxidation and Reduction Redox reactions – Transfer electrons from one reactant to another by and

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In oxidation – A substance electrons, or is oxidized In reduction – A substance 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 Oxidation of Organic Fuel Molecules During Cellular Respiration During cellular respiration – Glucose is oxidized and oxygen is reduced – Glucose is oxidized in a series of steps + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electrons from organic compounds Are usually first transferred to 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 the reduced form of NAD + – Passes the electrons to the electron transport chain

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

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 (takes place in the electron transport chain)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis – Breaks down glucose into two molecules of The Citric Acid Cycle – Completes the energy yielding oxidation of organic molecules

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 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 – 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

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 Energy investment 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 Energy payoff phase

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Before the citric acid cycle can begin Pyruvate must first be converted to 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 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 Citric Acid Cycle

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At the end of the chain In aerobic cellular respiration, electrons are passed to forming water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis: The Energy-Coupling Mechanism – 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 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 Chemiosmosis – Is an energy-coupling mechanism that uses energy in the form of a 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, in general, electron flow takes place in this sequence – Glucose to NADH to electron transport chain to oxygen – The ultimate product is, of course,

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 Concept 9.5: enables some cells to produce ATP without the use of oxygen Fermentation consists of – Glycolysis plus reactions that regenerate which can be reused by glyocolysis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation 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 In alcohol fermentation – Pyruvate is converted to ethanol in two steps; CO 2 is a by-product During lactic acid fermentation – Pyruvate is reduced directly by 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 Alcohol and Lactic Acid Fermentation 2 Pyruvate

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation and Cellular Respiration Compared Both fermentation and cellular respiration – Use to oxidize glucose and other organic fuels to pyruvate The final electron acceptor in – fermentation is an organic molecule – cellular respiration is an oxygen Cellular respiration – Produces a lot 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 Concept 9.6: 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