1. Cellular Respiration: Harvesting Chemical Energy AP Biology Ms. Haut

2. Energy Flow Energy flows into an ecosystem as sunlight and leaves as heat Photosynthesis generates oxygen and organic molecules, which are used in cellular respiration Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work

3. Catabolic Pathways and Production of ATP The breakdown of organic molecules is exergonic Fermentation is a partial degradation of sugars that occurs without oxygen Cellular respiration consumes oxygen and organic molecules and yields ATP Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + Energy (ATP + heat)

4. Cellular Respiration ATP-producing catabolic process in which the ultimate electron acceptor is an inorganic compound, Oxygen Most efficient catabolic pathway Is an exergonic process (ΔG = -686kcal/mol)

5. C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + Energy (ATP + Heat) Oxidation Reduction Electrons “fall” from Organic Molecules to Oxygen during Cellular Respiration

6. The Stages of Cellular Respiration: A Preview Cellular respiration has three stages: –Glycolysis (breaks down glucose into two molecules of pyruvate) –The Krebs Cycle (citric acid cycle) (completes the breakdown of glucose) –Oxidative phosphorylation (accounts for most of the ATP synthesis) The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions

7. Glycolysis Catabolic pathway Occurs in the cytosol Partially oxidizes glucose (6C) into two pyruvate (3C) molecules

8. Krebs Cycle Catabolic pathway Occurs in mitochondrial matrix Completes glucose oxidation by breaking down a acetyl-CoA into CO 2

9. Glycolysis and Krebs Cycle Together produce: Small amount of ATP by substrate-level phosphorylation NADH by transferring electrons from substrate to NAD+ Krebs Cycle also produces FADH 2 by transferring electrons to FAD+

10. Electron Transport Chain Located near inner membrane of mitochondrion Accepts energized electrons from reduced coenzymes (NADH and FADH 2 ) that are harvested during glycolysis and Krebs Cycle –Oxygen pulls electrons down ETC to a lower energy state

11. Oxidative Phosphorylation Accounts for almost 90% of the ATP generated by cellular respiration Energy released at each step of the ETC is stored in a form the mitochondrion can use to make ATP –Powered by redox reactions that transfer electrons from food to oxygen Small amount of ATP is produced directly by the enzymatic transfer of phosphate from an intermediate substrate in catabolism to ADP (substrate-level phosphorylation)

12. Glycolysis Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate Two major phases: –Energy investment phase –Energy payoff phase

13. Glycolysis

17. Conversion of Pyruvate to Acetyl CoA: Pyruvate Oxidation

18. Krebs Cycle http://library.thinkquest.org/C004535/media/kreb_cycle.gif

19. LE 9-12_1 ATP Glycolysis Oxidation phosphorylation Citric acid cycle Citric acid cycle Citrate Isocitrate Oxaloacetate Acetyl CoA H2OH2O

20. LE 9-12_2 ATP Glycolysis Oxidation phosphorylation Citric acid cycle Citric acid cycle Citrate Isocitrate Oxaloacetate Acetyl CoA H2OH2O CO 2 NAD + NADH + H +  -Ketoglutarate CO 2 NAD + NADH + H + Succinyl CoA

21. LE 9-12_3 ATP Glycolysis Oxidation phosphorylation Citric acid cycle Citric acid cycle Citrate Isocitrate Oxaloacetate Acetyl CoA H2OH2O CO 2 NAD + NADH + H +  -Ketoglutarate CO 2 NAD + NADH + H + Succinyl CoA Succinate GTP GDP ADP ATP FAD FADH 2 P i Fumarate

22. LE 9-12_4 ATP Glycolysis Oxidation phosphorylation Citric acid cycle Citric acid cycle Citrate Isocitrate Oxaloacetate Acetyl CoA H2OH2O CO 2 NAD + NADH + H +  -Ketoglutarate CO 2 NAD + NADH + H + Succinyl CoA Succinate GTP GDP ADP ATP FAD FADH 2 P i Fumarate H2OH2O Malate NAD + NADH + H +

24. Net Products Glycolysis: 2 pyruvate 2 NADH 2 ATP Pyruvate Oxidation: 2 NADH Krebs Cycle: 6 NADH 2 FADH 2 2 ATP

25. During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and the citric acid cycle, NADH and FADH 2 account for most of the energy extracted from food These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

26. The Pathway of Electron Transport The electron transport chain is in the cristae of the mitochondrion The carriers alternate reduced and oxidized states as they accept and donate electrons Electrons lose energy as they go down the chain and are finally passed to O 2, forming water The electron transport chain generates no ATP

27. LE 9-13 ATP Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle NADH 50 FADH 2 40 FMN FeS I FAD FeS II III Q FeS Cyt b 30 20 Cyt c Cyt c 1 Cyt a Cyt a 3 IV 10 0 Multiprotein complexes Free energy (G) relative to O2 (kcal/mol) H2OH2O O2O2 2 H + + 1 / 2

28. Chemiosmosis Electron transfer in the electron transport chain causes proteins to pump H + from the mitochondrial matrix to the intermembrane space H + then moves back across the membrane, passing through channels in ATP synthase ATP synthase uses the exergonic flow of H + to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H + gradient to drive cellular work

29. LE 9-14 INTERMEMBRANE SPACE H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP MITOCHONDRAL MATRIX ADP + P i A rotor within the membrane spins as shown when H + flows past it down the H + gradient. A stator anchored in the membrane holds the knob stationary. A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.

30. The energy stored in a H + gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis The H + gradient is referred to as a proton- motive force, emphasizing its capacity to do work

31. 1 NADH = 3 ATP 1 FADH 2 = 2 ATP 10 NADH = 30 ATP 2 FADH 2 = 4 ATP 34 ATP

33. Aerobic: existing in the presence of oxygen Anaerobic: existing in the absence of oxygen

34. Fermentation Cellular respiration requires O 2 to produce ATP Glycolysis can produce ATP with or without O 2 (in aerobic or anaerobic conditions) In the absence of O 2, glycolysis couples with fermentation to produce ATP

35. Fermentation Anaerobic catabolism of organic nutrients After pyruvate is produced in glycolysis, it is reduced, and NAD+ is regenerated –Prevents cell from depleting the pool of NAD+, needed in glycolysis –No additional ATP is produced

36. Organisms Classified by Oxygen Requirements Strict (obligate) aerobes —require O 2 for growth and metabolism Strict (obligate) anaerobes —only grow in the absence of O 2 (O 2 is toxic) Facultative anaerobes —capable of growing in either aerobic or anaerobic conditions

37. 1.NADH is oxidized to NAD+ and pyruvate is reduced to lactate (lactic acid) Commercially important products: cheese & yogurt Human muscle cells switch to lactic acid fermentation when O 2 is scarce. Lactate accumulates, slowly carried to liver and converted back to pyruvate when O 2 is available

38. 1.Pyruvate loses CO2 and is converted to the acetylaldehyde (2C) 2.NADH is oxidized to NAD+ and acetylaldehyde is reduced to ethanol (EtOH) Many bacteria and yeast carry out alcohol fermentation under anaerobic conditions

39. Alcohol Fermentation Yeast during brewing process http://www.langhambrewery.co.uk/content/ferme ntation-yeast.jpg Actively fermenting beer. The yeast mass is converting the sugars to alcohol and carbon dioxide. www.berkshirebrewingcompany.com/.../page4.h tml

40. Versatility of Catabolism Starch  glucose in digestive tract Liver converts glycogen  glucose Excess amino acids  pyruvate, acetyl CoA, and α-ketoglutarate Fats  glycerol + fatty acids Glycerol  glyceraldehyde phosphate Fatty acids  acetyl CoA (beta oxidation)

41. Biosynthesis Some organic molecules of food provide carbon skeletons or raw materials for making new macromolecules Some organic molecules from digestion used directly in anabolic pathways Some precursors come from glycolysis and Krebs Cycle Anabolic pathways require ATP produced from catabolic pathways

42. Feedback Mechanism of Control Ratio of ATP:ADP and AMP reflects energy status and phosphofructokinase is sensitive to changes in the ratio Citrate and ATP = allosteric inhibitors ADP and AMP = allosteric activators