Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Respiration: Harvesting Chemical Energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Contexts of Respiration – Breathing provides for the exchange of O 2 and CO 2 between an organism and its environment. CO 2 O2O2 O2O2 Bloodstream Muscle cells carrying out 4. Cellular Respiration 1. Breathing: bringing air into and out of the lungs Glucose  O 2 CO 2  H 2 O  ATP Lungs 2. External respiration: Exchange of O 2 & CO 2 between an organism (blood) and its environment 3. Internal respiration: Exchange of O 2 & CO 2 between the blood & body tissues be.com/watch?v =rGaP9nE8d9k A summary of cellular respiration

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 (O 2 ) is consumed as a reactant along with the organic fuel.” During cellular respiration, the fuel (such as 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 -1 In cellular respiration, glucose and other organic molecules are broken down in a series of steps. 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 O 2 → H 2 O How would these electrons make the trip from NADH to the oxygen? 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 Oxidation: Loss of electrons. Reduction: Gain of electrons. Redox reactions require both a donor and an acceptor of electrons. Oxidation-Reduction Reactions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NADH + H + 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? My friend NADH, Let your electrons take the steps down. Slowly, but surely

LE 9-4 NAD + Nicotinamide (oxidized form) Dehydrogenase 2 e – + 2 H + 2 e – + H + NADH H+H+ H+H+ Nicotinamide (reduced form) + 2[H] (from food) + Electrons from organic compounds, such as glucose, are usually first transferred to NAD +, a coenzyme, to form NADH. NAD + + 2e - + 2H + ↔ NAD + H + + H + - -

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 NAD  NADH HH Glucose 2 Pyruvate ATP 2 P 2 ADP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvate Glucose CYTOSOL No O 2 present Fermentation Ethanol or lactate Acetyl CoA MITOCHONDRION O 2 present Cellular respiration Citric acid cycle

CYTOSOL Pyruvate NAD + MITOCHONDRION Transport protein NADH + H + Coenzyme ACO 2 Acetyl Co A The Intermediate Stage Between Glycolysis and the Citric Acid Cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Intermediate Stage Between Glycolysis and the Citric Acid Cycle CO 2 Pyruvate NAD  NADH  H  CoA Acetyl CoA (acetyl coenzyme A) Coenzyme A

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 FADH 2 – 2 CO 2. The Citric Acid Cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Mitochondrion Mitochondrion Intermembrane space Outer membrane Inner membrane Cristae Matrix 100 nm Mitochondrial DNA Free ribosomes in the mitochondrial matrix

Mitochondrion Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation Citric acid cycle Glycolysis and the Citric Acid Cycle

Pyruvate (from glycolysis, 2 molecules per glucose) ATP Glycolysis Oxidation phosphorylation Citric acid cycle NAD + NADH + H + CO 2 CoA Acetyl CoA CoA Citric acid cycle CO NAD H + NADH3 ATP ADP + P i FADH 2 FAD The Citric Acid Cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Respiration—Aerobic Cellular Respiration: Citric Acid Cycle Two “turns” of the citric acid cycle produce: 2 ATP 6 NADH 2 FADH 2 What energy molecules are produced in breaking down one molecule of glucose in the citric acid cycle?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 substrate- level phosphorylation. The rest of 32 ATP ( ____ ATP) will be formed by oxidative phosphorylation. 2- Oxidative Phosphorylation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2- Oxidative Phosphorylation ctron_transport/electron_transport.swf ctron_transport/electron_transport.swf

LE 9-6_3 Mitochondrion Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation ATP Substrate-level phosphorylation Citric acid cycle ATP Oxidative phosphorylation Oxidative phosphorylation: electron transport and chemiosmosis Electrons carried via NADH Electrons carried via NADH and FADH 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation: 1- The Electron Transport Chain 3 4

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 O 2, forming water.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation: 1- Electron Transport Chain / Generation of Proton Motive Force 3 4

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation: 2- Chemiosmosis

Protein complex of electron carriers H+H+ ATP Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle H+H+ Q III I II FAD FADH 2 + H + NADH NAD + (carrying electrons from food) Inner mitochondrial membrane Inner mitochondrial membrane Mitochondrial matrix Intermembrane space H+H+ H+H+ Cyt c IV 2H / 2 O 2 H2OH2O ADP + H+H+ ATP synthase Electron transport chain Electron transport and pumping of protons (H + ), Which create an H + gradient across the membrane P i Chemiosmosis ATP synthesis powered by the flow of H + back across the membrane Oxidative phosphorylation Oxidative Phosphorylation (Summary): 1- The electron transport chain 2- Chemiosmosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation (Summary): 1- The electron transport chain 2- Chemiosmosis Matrix of the mitochondrion Inter-membrane space

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H2OH2O e-e- Electrons are transferred from NADH and FADH 2 through a series of electron carriers within the cristae. O 2 is the final electron acceptor. Energy of electrons “falling” is used to move H+ up its concentration gradient from the matrix to the outer compartment. ATP synthetase harnesses the kinetic energy of the H+ “falling” down its concentration gradient to bond ADP and Pi to form ATP NADH Glycolysis Intermediate stage NADH FADH 2 Citric acid cycle ATP 1 2 O 2 e-e- e-e- H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Electron carriers Matrix H + pumps ATP synthetase ADP PiPi Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxidative Phosphorylation (Summary): 1- The electron transport chain 2- Chemiosmosis

LE 9-16 CYTOSOL Electron shuttles span membrane 2 NADH or 2 FADH 2 MITOCHONDRION Oxidative phosphorylation: electron transport and chemiosmosis 2 FADH 2 2 NADH6 NADH Citric acid cycle 2 Acetyl CoA 2 NADH Glycolysis Glucose 2 Pyruvate + 2 ATP by substrate-level phosphorylation + 2 ATP by substrate-level phosphorylation + about 26 or 28 ATP by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol About 30 or 32 ATP Maximum per glucose: A summary of cellular respiration