Chapter 8 - Cellular Respiration

Chapter 8 - Cellular Respiration - Aerobic Respiration and...

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Unformatted text preview: Aerobic Respiration and Other Energy-Releasing Pathways Energy-Releasing Chapter 8 Evolution of Metabolic Evolution Pathways When life originated, atmosphere had little oxygen oxygen Earliest organisms used anaerobic pathways Later, noncyclic pathway of photosynthesis Later, increased atmospheric oxygen increased Cells arose that used oxygen as final acceptor in Cells electron transport electron Main Types of Energy-Releasing Pathways Anaerobic pathways Evolved first Don’t require oxygen Starts with glycolysis in Starts cytoplasm cytoplasm Completed in cytoplasm Oxygen is NOT the final Oxygen electron acceptor electron Aerobic pathways Aerobic Evolved later Require oxygen Start with glycolysis in Start cytoplasm cytoplasm Completed in Completed mitochondria mitochondria Oxygen is the final Oxygen electron acceptor electron ANAEROBIC PATHWAY AEROBIC PATHWAY Processes Are Linked sunlight energy PHOTOSYNTHESIS water + carbon dioxide sugar molecules oxygen AEROBIC RESPIRATION In-text figure Page 146 Summary Equation for Aerobic Summary Respiration Respiration C6H1206 + 6O2 glucose oxygen 6CO2 + 6H20 carbon dioxide dioxide water CYTOPLASM 2 glucose ATP 4 Glycolysis e- + H+ (2 ATP net) 2 pyruvate 2 NADH MITOCHONDRION Overview of Aerobic Krebs Respiration Respiration Cycle 2 NADH 6 NADH e- + H+ e- 2 CO2 e- + H+ 4 CO2 e +H - 2 FADH2 ATP + 2 Electron Transfer Phosphorylation H+ 32 ATP ATP water e- + oxygen Typical Energy Yield: 36 ATP Figure 8.3 Page 135 Summary of Energy Harvest Summary (per molecule of glucose) Glycolysis – 2 ATP (net) formed by substrate-level phosphorylation Krebs cycle and preparatory reactions – 2 ATP formed by substrate-level phosphorylation Electron transport phosphorylation – 32 ATP formed TOTAL => ABOUT 36 ATP FORMED The Coenzymes The NAD+ and FAD accept electrons and hydrogen Become NADH and FADH2 Become Deliver electrons and hydrogen to the Deliver electron transfer chain Energy-Requiring Steps Steps Energy-Requiring Steps of Glycolysis 2 ATP invested glucose ATP ADP ATP energy activates ATP glucose and its sixglucose carbon derivatives 2 ATP invested 1 Glucose Figure 8.4(2) Page 137 2 PGAL P glucose-6-phosphate P fructose-6-phosphate ATP ADP P P fructose1,6-bisphosphate P PGAL P PGAL Glycolysis: Net Energy Yield Energy requiring steps: Energy 2 ATP invested ATP Energy releasing steps: Energy 2 NADH formed NADH 4 ATP formed ATP Net yield is 2 ATP and 2 NADH per glucose Second Stage Reactions Preparatory reactions Preparatory – Pyruvate is oxidized into two-carbon acetyl Pyruvate units and carbon dioxide units – NAD+ is reduced Krebs cycle – The acetyl units are oxidized to carbon The dioxide dioxide – NAD+ and FAD are reduced and -CoA acetyl-CoA Krebs Cycle Cycle Overall Products Coenzyme A Coenzyme 2 CO2 CO 3 NADH NADH FADH2 FADH ATP ATP CoA oxaloacetate citrate NADH H2O NAD+ H2 O malate + NAD H2 O FADH2 isocitrate NADH fumarate O α -ketoglutarate FAD NAD+ succinate NADH CoA O succinyl-CoA Figure 8.6 Page 139 ATP O ADP + phosphate group O The Krebs Cycle The Overall Reactants Acetyl-CoA 3 NAD+ FAD ADP and Pi Overall Products Coenzyme A 2 CO2 3 NADH FADH2 ATP Note: Two turns of the Krebs Cycle occurs for each glucose molecule being metabolized Results of the Second Stage Results All of the carbon molecules in pyruvate end up in All carbon dioxide carbon Coenzymes are reduced (they pick up electrons Coenzymes and hydrogen) and One molecule of ATP forms for each cycle Four-carbon oxaloacetate regenerates for Four-carbon another round of the Krebs cycle another Coenzyme Reductions during First Two Stages (per one glucose) (per Glycolysis Preparatory reactions Krebs cycle 2 NADH 2 NADH NADH 2 FADH2 + 6 NADH Total 2 FADH2 + 10 NADH Electron Transfer Chain Electron Occurs in the mitochondria Occurs Coenzymes deliver electrons to electron Coenzymes transfer chains transfer Electron transfer sets up H+ ion gradients Flow of H+ down gradients powers ATP formation formation Making ATP: Chemiosmotic Model Chemiosmotic MATRIX (INNER COMPARTMENT) ATP ADP + Pi Importance of Oxygen Importance Electron transport phosphorylation Electron requires the presence of oxygen requires Oxygen withdraws spent electrons from Oxygen the electron transfer chain, then combines with H+ to form water with Energy Harvest Varies Energy NADH formed in cytoplasm cannot enter NADH mitochondrion mitochondrion It delivers electrons to mitochondrial It membrane membrane Membrane proteins shuttle electrons to Membrane NAD+ or FAD inside mitochondrion NAD Electrons given to FAD yield less ATP than those given to NAD+ than Efficiency of Aerobic Respiration 686 kcal of energy are released 7.5 kcal are conserved in each ATP 7.5 When 36 ATP form, 270 kcal (36 X 7.5) When are captured in ATP are Efficiency is 270 / 686 X 100 = 39 percent Efficiency Most energy is lost as heat Most Anaerobic Pathways Anaerobic Do not use oxygen Do Produce less ATP than aerobic pathways Two types – Fermentation pathways – Anaerobic electron transport Fermentation Pathways Fermentation Begin with glycolysis Do not break glucose down completely to carbon Do dioxide and water dioxide Yield only the 2 ATP from glycolysis Steps that follow glycolysis serve only to Steps regenerate NAD+ regenerate Lactate Fermentation Lactate GLYCOLYSIS C6H12O6 2 ATP energy input 2 NAD+ 2 ADP 2 4 NADH ATP energy output 2 pyruvate 2 ATP net LACTATE FORMATION electrons, hydrogen from NADH 2 lactate GLYCOLYSIS C6H12O6 Alcoholic Fermentation 2 ATP energy input 2 NAD+ 2 ADP 2 4 NADH ATP 2 pyruvate energy output 2 ATP net ETHANOL FORMATION 2 H2O 2 CO2 2 acetaldehyde electrons, hydrogen from NADH 2 ethanol Anaerobic Electron Transport Anaerobic Carried out by certain bacteria Electron transfer chain is in bacterial Electron plasma membrane Final electron acceptor is compound from environment (such as nitrate), not oxygen environment ATP yield is low FOOD fats fatty acids glycerol complex carbohydrates proteins simple sugars glycogen amino acids glucose-6-phosphate GLYCOLYSIS PGAL NH3 carbon backbones urea pyruvate acetyl-CoA Figure 8.11 Page 145 KREBS CYCLE Alternative Energy Sources Alternative ...
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