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How Cells Release Stored Energy – Cellular Respiration

How Cells Release Stored Energy – Cellular Respiration. Aerobic Respiration: Whole Organism. Aerobic respiration at the whole organism level = process by which gases are exchanged with the environment. O 2. CO 2. Aerobic Respiration: Whole Organism.

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How Cells Release Stored Energy – Cellular Respiration

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  1. How Cells Release Stored Energy – Cellular Respiration

  2. Aerobic Respiration: Whole Organism • Aerobic respiration at the whole organism level = process by which gases are exchanged with the environment. O2 CO2

  3. Aerobic Respiration: Whole Organism • Respiratory Surface (= part of the organism where O2 diffuses into and CO2 diffuses out of the organism) must be moist, as gases must be dissolved in water before they can diffuse in or out. http://www.go-epix.net/uploadedimages/Water%20drop%20ks16870%208050114134057.JPG

  4. Aerobic Respiration: Whole Organism In unicellular aquatic protozoans: O2 dissolved in water passes across the cell membrane by diffusion, and CO2 exits. CO2 O2

  5. Aerobic Respiration: Whole Organism In multicellular aquatic plants and invertebrate animals: O2 dissolved in water enters cells by diffusion, and CO2 exits by diffusion. Planarian CO2 O2 Elodeacell http://www.cdb.riken.jp/jp/04_news/img/planarian300.jpg

  6. Aerobic Respiration: Whole Organism In insects: O2 enters through small openings in the body wall (spiracles) and is carried through tracheal tubes to moist cell membranes, across which respiratory exchange occurs. Spiracles spiracle SEM

  7. Aerobic Respiration: Whole Organism In fish: O2 (in H2O) diffuses across the surface of gills, into capillaries of the circulatory system and CO2 diffuses in the opposite direction.

  8. Cellular Respiration:THE BIG PICTURE • Cellular respiration is the process by which organisms can get energy (ATP) from their food (glucose) • Cellular respiration is CRITICAL for life • Occurs in BOTH plants and animals • Two main mechanisms • Aerobic cellular Respiration – Requires Oxygen • Anaerobic cellular Respiration –Does not require Oxygen

  9. Aerobic Respiration Evolved later Require oxygen Start with glycolysis in cytoplasm Completed in mitochondria Anaerobic Respiration Evolved first Don’t require oxygen Start with glycolysis in cytoplasm Completed in cytoplasm Main Types of Cellular Respiration Pathways

  10. Aerobic Respiration • Overall Equation: C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water dioxide • Several steps occur in the middle (intermediates) • Each step (rxn) catalyzed by enzymes

  11. Aerobic respiration Overview Stage One: • Glycolysis (cytoplasm) Stage Two: • Preparation for Krebs (mitochondrial matrix) • Krebs Cycle (matrix) Stage Three: • Electron Transfer Chain (across inner membrane of mitochondria)

  12. The Role of Carrier Molecules • Several oxidation-reduction rxns take place in aerobic respiration (Glucose gets oxidized to carbon dioxide) • In order to aid in the redox rxns, enzymes use carrier molecules NAD+ and FAD to carry electrons from broken down glucose to the electron transfer chain • NAD+ and FAD accept electrons and hydrogen to become NADH and FADH2during the first two stages of aerobic respiration (Glycolysis, Krebs) and deliver electrons and hydrogen to the Electron Transfer Chain to make ATP

  13. Stage One: Glycolysis • Glucose (6-carbon) is broken down into 2 molecules of pyruvate (3-carbon) • Yields 2 ATP by substrate level phosphorylation

  14. Glycolysis: Overall Reaction 2 ATP 2 ADP G3P (3C) Pyruvate (3C) 2 NADH 2 NAD+ 2 ADP 2 ATP Glucose (6C) Fructose Bisphosphate (6C) 2 NADH 2 NAD+ G3P (3C) Pyruvate (3C) 2 ATP 2 ADP

  15. Aerobic Respiration:1. Glycolysis

  16. Glycolysis: Net Yield Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield: 2 ATP + 2 NADH + 2 molecules of Pyruvic Acid

  17. What happens next? • Depends on the organism and the presence of oxygen • If oxygen is around: Aerobic respiration, proceed to Krebscycle • If no oxygen: Anaerobic respiration, Proceed to Fermentation

  18. Second Stage: Krebs cycle • Preparatory reactions: Oxidation of pyruvate • Pyruvic acid is oxidized into two-carbon acetyl CoA units and carbon dioxide • NAD+ is reduced into NADH2 • Krebs cycle • The acetyl units are oxidized to carbon dioxide • NAD+and FAD are reduced into FADH and NAHD2

  19. Oxidation of Pyruvate

  20. Overall Products Coenzyme A 2 CO2 3 NADH FADH2 ATP Overall Reactants Acetyl-CoA 3 NAD+ FAD ADP and Pi The Krebs Cycle

  21. Results of the Second Stage • All of the carbon atoms in pyruvate end up in carbon dioxide • NAD and FAD are reduced (they pick up electrons and hydrogen) • One molecule of ATP forms • Four-carbon oxaloacetate regenerates

  22. NAD/FAD Reductions during First Two Stages • Glycolysis 2 NADH2 • Preparatory reactions 2 NADH2 • Krebs cycle 2 FADH2 + 6 NADH2 • Total 2 FADH2 + 10 NADH2

  23. Electron Transfer Chain • Occurs in the mitochondria • Coenzymes deliver electrons to electron transfer chains • Electron transfer sets up H+ ion gradients • Flow of H+ down gradients powers ATP formation

  24. Importance of Oxygen • Oxygen is the finial Electron acceptor • Electron transport chain requires the presence of oxygen • Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water

  25. Summary of Energy Harvest(per molecule of glucose) • Glycolysis • 2 ATP formed by • Krebs cycle and preparatory reactions • 2 ATP formed • Electron transport chain • 32 ATP formed

  26. Efficiency of Aerobic Respiration • 686 kcal of energy are released • 7.5 kcal are conserved in each ATP • When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP • Efficiency is 270 / 686 X 100 = 39 percent • Most energy is lost as HEAT!

  27. Anaerobic Pathways • Do not use oxygen • Produce less ATP than aerobic pathways

  28. Fermentation Pathways • Begin with glycolysis • Do not break glucose down completely to carbon dioxide and water • Yield only the 2 ATP from glycolysis • Steps that follow glycolysis serve only to regenerate NAD+

  29. Evolution of Metabolic Pathways • When life originated, atmosphere had little oxygen • Earliest organisms used anaerobic pathways • Later, noncyclic pathway of photosynthesis increased atmospheric oxygen • Cells arose that used oxygen as final acceptor in electron transport

  30. Summary of Cellular Respiration

  31. ATP / ADP Cycle • ATP is constantly being used and remade in the cell. • Energy is released or stored by breaking or making a phosphate bond. http://www.columbia.edu/cu/biology/courses/c2005/purves6/figure06-09.jpg

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