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Cellular Respiration: Harvesting Chemical Energy Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Contexts of Respiration – Breathing provides for the exchange of O2 and CO2 between an organism and its environment. O2 A summary of cellular respiration http://www.youtu be.com/watch?v =rGaP9nE8d9k CO2 1. Breathing: bringing air into and out of the lungs Lungs CO2 Bloodstream 2. External respiration: Exchange of O2 & CO2 between an organism (blood) and its environment O2 3. Internal respiration: Exchange of O2 & CO2 between the blood & body tissues Muscle cells carrying out 4. Cellular Respiration Glucose + O2 CO2 + H2O + ATP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidation of Organic Fuel Molecules During Cellular Respiration • Cellular respiration may be defined as “A catabolic process that produces ATP when oxygen (O2) is consumed as a reactant along with the organic fuel.” • During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced: becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest via NAD+ and the Electron Transport Chain -1 • In cellular respiration, glucose and other organic molecules are broken down in a series of steps. becomes oxidized C6H12O6 + 6O2 6CO2 + 6H2O + Energy becomes reduced • Glucose loses electrons (i.e. it gets oxidized). • NADH and FADH2 carry these electrons and eventually deliver them to oxygen to form water 2e- + 2H+ + ½ O2 → H2O How would these electrons make the trip from NADH to the oxygen? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidation-Reduction Reactions Oxidation: Loss of electrons. Reduction: Gain of electrons. Redox reactions require both a donor and an acceptor of electrons. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings My friend, oxygen, I want to give you TWO electrons so you can form water. Shall I deliver these TWO electrons in one dangerous and quick step or let them take the safe steps down? NADH + H+ My friend NADH, Let your electrons take the steps down. Slowly, but surely Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 9-4 2 e– + 2 H+ 2 e– + H+ NAD+ H+ NADH Dehydrogenase + 2[H] (from food) + H+ Nicotinamide (reduced form) Nicotinamide (oxidized form) Electrons from organic compounds, such as glucose, are usually first transferred to NAD+, a coenzyme, to form NADH. NAD+ + 2e- + 2H+ ↔ - NAD+H+ + H+ 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 © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Simplified model of glycolysis 2 NAD+ 2 NADH + 2 H+ Glucose 2 Pyruvate 2 ADP +2 P 2 ATP http://www.youtube.com/watch?v=3GTjQTqUuOw Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Intermediate Stage Between Glycolysis and the Citric Acid Cycle MITOCHONDRION CYTOSOL NAD+ NADH + H+ Acetyl Co A Pyruvate Transport protein CO2 Coenzyme A The Intermediate Stage Between Glycolysis and the Citric Acid Cycle NAD+ NADH + H+ CoA Pyruvate Acetyl CoA (acetyl coenzyme A) CO2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Coenzyme A The Citric Acid Cycle • The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix • The cycle oxidizes acetyl CoA (the organic fuel derived from pyruvate), generating the following per one turn of the cycle: – 1 ATP – 3 NADH – 1 FADH2 – 2 CO2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Mitochondrion Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis and the Citric Acid Cycle http://www.youtube.com/watch?v=-cDFYXc9Wko Glycolysis Pyruvate Glucose Cytosol Citric acid cycle Mitochondrion ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Pyruvate (from glycolysis, 2 molecules per glucose) CO2 NAD+ Glycolysis Citric acid cycle ATP ATP Oxidation phosphorylation CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle FADH2 2 CO2 3 NAD+ 3 NADH + 3 H+ FAD ADP + P i ATP ATP Cellular Respiration—Aerobic Cellular Respiration: Citric Acid Cycle What energy molecules are produced in breaking down one molecule of glucose in the citric acid cycle? Two “turns” of the citric acid cycle produce: 2 ATP 6 NADH 2 FADH2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2- Oxidative Phosphorylation • One glucose molecule would yield a maximum of 32 ATP via cellular respiration. • Glycolysis yields ___ ATP by substrate-level phosphorylation. • The citric acid cycle yields ___ ATP by substratelevel phosphorylation. • The rest of 32 ATP ( ____ ATP) will be formed by oxidative phosphorylation. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2- Oxidative Phosphorylation • http://www.wiley.com/legacy/college/boyer/0470003790/animations/ele ctron_transport/electron_transport.swf Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 9-6_3 Electrons carried via NADH and FADH2 Electrons carried via NADH Glycolysis Pyruvate Glucose Cytosol Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Mitochondrion ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation Oxidative Phosphorylation: 1- The Electron Transport Chain 3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 Oxidative Phosphorylation: 1- The Electron Transport Chain • 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 O2, forming water. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation: 1- Electron Transport Chain / Generation of Proton Motive Force 3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 Oxidative Phosphorylation: 2- Chemiosmosis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation (Summary): 1- The electron transport chain 2- Chemiosmosis Glycolysis Citric acid cycle ATP ATP Inner mitochondrial membrane Oxidative phosphorylation: electron transport and chemiosmosis ATP H+ H+ H+ H+ Intermembrane space Cyt c Protein complex of electron carriers Q IV III I ATP synthase II Inner mitochondrial membrane FADH2 NADH + H+ 2H+ + 1/2 O2 H2O FAD NAD+ Mitochondrial matrix ATP ADP + P i (carrying electrons from food) H+ Electron transport chain Electron transport and pumping of protons (H+), Which create an H+ gradient across the membrane Oxidative phosphorylation Chemiosmosis ATP synthesis powered by the flow of H+ back across the membrane Oxidative Phosphorylation (Summary): 1- The electron transport chain 2- Chemiosmosis Inter-membrane space Matrix of the mitochondrion Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation (Summary): 1- The electron transport chain 2- Chemiosmosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis NADH NADH Intermediate stage Matrix NADH e- FADH2 Citric acid cycle e- ATP 1 O 2 2 e- ADP + Pi H+ ATP synthetase H2O H+ H+ H+ H+ H+ H+ H+ H+ Electron carriers H+ pumps 1 Electrons are transferred from NADH and FADH2 through a series of electron carriers within the cristae. O2 is the final electron acceptor. 2 Energy of electrons “falling” is used to move H+ up its concentration gradient from the matrix to the outer compartment. 3 ATP synthetase harnesses the kinetic energy of the H+ “falling” down its concentration gradient to bond ADP and Pi to form ATP. http://www.youtube.com/watch?v=kN5MtqAB_Yc&feature=related Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 9-16 Electron shuttles span membrane CYTOSOL 2 NADH 2 NADH Glycolysis Glucose MITOCHONDRION 2 NADH or 2 FADH2 2 Pyruvate 2 Acetyl CoA 6 NADH Citric acid cycle + 2 ATP + 2 ATP by substrate-level phosphorylation by substrate-level phosphorylation Maximum per glucose: 2 FADH2 Oxidative phosphorylation: electron transport and chemiosmosis + about 26 or 28 ATP by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol About 30 or 32 ATP A summary of cellular respiration http://www.youtube.com/watch?v=rGaP9nE8d9k