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Fig. 9.1 Outline – Cellular Respiration Respiration • Cellular Energy Harvest: an Overview • Stages of Aerobic Cellular Respiration – Glycolysis – Oxidation of Pyruvate – Krebs Cycle – Electron Transport Chain • Anaerobic Respiration and Fermentation • Catabolism of Protein and Fat Energy to Drive Metabolism • Autotrophs – use inorganic sources of energy Photoautotrophs – harvest sunlight – convert radiant energy into chemical energy. Chemoautotrophs Cellular Respiration Metabolic pathways Æ series of reactions Æ oxidations – loss of electrons Æ dehydrogenations hydrogen atom (1 electron, 1 proton). – harvest energy from inorganic sources – S, NH3, NH2, H2S, Fe+2 • Heterotrophs – use organic sources of energy – live off energy produced by autotrophs. – extract energy from food catabolism – Uuse cellular respiration to extract energy 1 Cellular Aerobic Respiration Cellular Respiration • How do cells harvest energy – cells break chemical bonds – shift electrons from molecule to molecule Glucose molecules broken down to CO2 Glucose loses electrons (as hydrogen atoms) to oxygen Cells tap energy from electrons Cells bank energy in ATP • Where do the electrons go? Loss of hydrogen atoms (oxidation) – Aerobic respiration • final electron acceptor is oxygen C6H12O6 – Anaerobic respiration + 6 CO2 + 6 H2O 6 O2 + Glucose (ATP) Energy Gain of hydrogen atoms (reduction) • final electron acceptor is not oxygen ΔG = -686kcal/mol glucose Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transferring Energy Transferring Energy – Electron Transport Chain Oxidation - Dehydrogenase removes electrons from substrate 1. NADH passes electrons to an electron transport chain 2. Energy is released as electrons “fall” and lose energy Reduction - Electrons in Hydrogen Transferred to NAD+ NADH H Oxidation H O Dehydrogenase O + 2H (Enzyme) NAD + + 2H 2H + Reduction + 2e− Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings NADH + (carries 2 electrons) NAD + + H + ATP 2e− Controlled release of energy for ATP synthesis H+ Electron Transport Chain H+ 2e− O2 H2O Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 9.6 (TEArt) Aerobic Respiration Oxidation of Glucose Aerobic Respiration Stage 1: Glycolysis 1 2 3 6-carbon glucose (Starting material) 2 ATP Complete oxidation of glucose proceeds in 4 stages 1. glycolysis 2. pyruvate oxidation 3. Krebs cycle (citric acid cycle) 4. electron transport chain & chemiosmosis P P P 6-carbon sugar diphosphate P 6-carbon sugar diphosphate P P P 3-carbon sugar 3-carbon sugar phosphate phosphate P 3-carbon sugar 3-carbon sugar phosphate phosphate NADH NADH 2 ATP 2 ATP 3-carbon pyruvate 3-carbon pyruvate Priming reactions. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 9.7a (TEArt) 1. Priming 3. Energy Harvest CH2 O O 7. Removal of high-energy phosphate by two ADP molecules produces two ATP molecules and leaves two 3PG molecules. P Phosphoglucose isomerase CH2 O O P ATP P 3 Phosphofructokinase P O ADP Electron transport chain CH2 O CH2 O P 8–9. Removal of water yields two PEP molecules, each with a high-energy phosphate bond. O CH2 C O Dihydroxyacetone CH2OH phosphate 2. Cleavage Glyceraldehyde 3 -phosphate (G3P) H C O CHOH CH2 O P Pi NAD+ Pi 6 3. Energy Harvest Glyceraldehyde NADH NADH 3-phosphate P O C O dehydrogenase CHOH 1,3-Bisphosphoglycerate 1,3-Bisphosphoglycerate CH2 O P (BPG) (BPG) NAD+ 7 Phosphoglycerate kinase 3-Phosphoglycerate (3PG) OC CHOH 3-Phosphoglycerate (3PG) 2-Phosphoglycerate (2PG) ADP C O H C O CH2OH 2-Phosphoglycerate (2PG) P OH2O C Phosphoenolpyruvate (PEP) 10 Pyruvate kinase ATP Pyruvate O P CH2 O- 9 Enolase Phosphoenolpyruvate (PEP) 10. Removal of high-energy phosphate by two ADP molecules produces two ATP molecules and two pyruvate molecules. ADP ATP 8 Phosphoglyceromutase H2O Fructose 1,6-bisphosphate 4,5 Aldolase Isomerase ADP ATP CH2OH Fructose 6-phosphate Krebs cycle 1,3-Bisphosphoglycerate (BPG) Glycolysis - Steps O Glucose 6-phosphate 2 Pyruvate oxidation 6. Oxidation followed by phosphorylation produces two NADH molecules and two molecules of BPG, each with one high-energy phosphate bond. CH2OH ADP Glycolysis 4–5. Six-carbon molecule split into 2 three-carbon molecules one G3P & dhap which is converted to G3P Fig. 9.7b (TEArt) Glucose 1 ATP Hexokinase 1. Priming Energy-harvesting reactions. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis - Steps Glucose Cleavage reactions. ADP ATP Pyruvate O C O CH2 P OC OHarvest 3. Energy C O CH3 3 Glycolysis - Summary Glycolysis = Catabolic pathway 10 biochemical steps Major Stages 1. Priming 2. Cleavage 3. Energy Harvesting Substrate-level phosphorylation Nets 2 ATP molecules Nets 2 pyruvates Nets 2 NADH Universal: All living organisms 1. Releases CO2 2. Produces NADH and acetyl Coenzyme A 3. Acetyl CoA is transferred to the mitochondrion Pyruvate in cytoplasm Outer mitochondrial membrane Inner mitochondrial membrane Aerobic Respiration Stage 3: Krebs Cycle Mitochondrion Aerobic Respiration Stage 3: KREBS CYCLE Aerobic Respiration Stage 2 Oxidation of Pyruvate 4 Krebs Cycle Summary 1. Location: Mitochondrial matrix 2. Loss of 2 CO2 = completion of pyruvate oxidation 3. ATP synthesis 4. Reduction of Coenzymes…for each turn of cycle: ¾ 3 NAD+ Æ 3 NADH… or 6 for each glucose ¾ 1 FAD Æ 1 FADH2 …or 2 for each glucose Mitochondrion Structure Glycolysis + Pyruvate Oxidation + Krebs Cycle After glycolysis, pyruvate oxidation, and the Krebs cycle, glucose has been oxidized to: - 6 CO2 - 4 ATP - 10 NADH Proceed to electron transport chain. - 2 FADH2 Stage 4: Oxidative Phosphorylation 1.Electron Flow occurs in mitochondrial membrane 2.Protons are transported across the inner mitochondrial membrane H2O 3.ATP is synthesized by Chemiosmosis H+ H+ H+ H+ H+ H+ H+ H+ H+ . Outer Membrane Intermembrane Space Cristae Inner Membrane H Intermembrane space Inner mitochondrial membrane Matrix + H ee- FADH2 NAD+ NADH Mitochondrial matrix H+ H+ H+ FAD H+ H+ H + H+ H+ H+ H+ + H+ H+ + O H Electron Transport Chain H2O Figure 6.10 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 5 Stage 4: Oxidative Phosphorylation Stage 4: Oxidative Phosphorylation ATP Synthesis by Chemiosmosis H+ ++ H ++ H H H+ H+ H+ H+ H+ H+ H+ + H+ H+ H+ H+ H+ H H+ Electron Transport Chain ADP P H+ 1. Occurs in the mitochondria 2. Uses the energy released by electrons to pump H+ across a membrane 3. Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP ATP H+ H+ Chemiosmosis by ATP synthase Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 9.5 (TEArt) Oxidation-Reduction and Aerobic Respiration Aerobic Cellular Respiration – Overview Cytoplasm Glucose 1. Glycolysis 2. Pyruvate oxidation 3. Krebs (Citric Acid) Cycle NADH Glycolysis ATP 4. Electron Transport Chain Pyruvate Pyruvate oxidation AcetylCoA NADH NADH Krebs cycle CO2 Intermembrane space Mitochondrial matrix CO2 ATP FADH2 H2O e- ATP NAD+ and FAD Electron transport chain Inner mitochondrial membrane Mitochondrion 6 ATP Synthesis & Oxidation of Glucose Aerobic Respiration Cells are able to make ATP via: 1. substrate-level phosphorylation – transferring a phosphate directly to ADP from another molecule 2. oxidative phosphorylation – use of ATP synthase and energy derived from a proton (H+) gradient to make ATP Recycling NADH – With continuous Glycolysis • NADH Increases • NAD+ Decreases – NADH must be recycled into NAD+ 1. aerobic respiration Æ NADH oxidized in mitochondria 2. anaerobic respiration Æ NADH oxidized another way Æ fermentation = use of organic molecules as final electron acceptor Æ anaerobic respiration = use of inorganic molecule as e- acceptor Sulfate-reducing bacteria Methanogenic bacteria Fate of Pyruvate Summary: Respiration without oxygen 1. Glycolysis produces a net of 2ATP 2. Fermentation - recycles NADH to NAD+ Lactic acid fermentation CO2 and Ethanol fermentation 3. Anaerobic Respiration Methanogens CO2 Æ CH4 SulfateSulfate-reducing Bacteria SO4 Æ H2S 28 7 Fig. 9.20 (TEArt) Respiration Efficiency Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy Sources for Cellular Respiration Macromolecules Cell building blocks Nucleic Proteins Polysaccharides acids Nucleotides Amino acids Sugars Fats Fatty acids Pyruvate Oxidative respiration Acetyl-CoA Krebs cycle Metabolic Waste products Fig. 9.23 (TEArt) NH3 H2O CO2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fermentation Alcohol fermentation H H C OH CH3 2 Ethanol Glucose 2 ADP 2 ATP O– C O C O CH3 G L Y C O L Y S I S 2 NADH CO2 2 Pyruvate Lactic acid fermentation Glucose 2 ADP 2 ATP O– C O C O CH3 2 NAD+ G L Y C O L Y S I S H C O CH3 2 Acetaldehyde O– C O H C OH CH3 2 NAD+ 2 Lactate 2 NADH 2 Pyruvate 8