1. How Cells Release Stored Energy Chapter 8

2. 8.1 Main Types of Energy-Releasing Pathways Aerobic pathways Evolved later Require oxygen Start with glycolysis in cytoplasm Completed in mitochondria Anaerobic pathways Evolved first Don’t require oxygen Start with glycolysis in cytoplasm Completed in cytoplasm

3. Summary Equation for Aerobic Respiration C 6 H 12 0 6 + 6O 2 6CO 2 + 6H 2 0 glucose oxygen carbon water dioxide

4. Overview of Aerobic Respiration CYTOPLASM Glycolysis Electron Transfer Phosphorylation Krebs Cycle ATP 2 CO 2 4 CO 2 2 32 water 2 NADH 8 NADH 2 FADH 2 2 NADH 2 pyruvate e - + H + e - + oxygen (2 ATP net) glucose Typical Energy Yield: 36 ATP e-e- e - + H + ATP H+H+ e - + H + ATP 2 4 Figure 8.3 Page 135

5. The Role of Coenzymes NAD + and FAD accept electrons and hydrogen Become NADH and FADH 2 Deliver electrons and hydrogen to the electron transfer chain

6. A simple sugar (C 6 H 12 O 6 ) Atoms held together by covalent bonds Glucose In-text figure Page 136 8.2 GLYCOLYSIS

7. Glycolysis Occurs in Two Stages Energy-requiring steps –ATP energy activates glucose and its six-carbon derivatives Energy-releasing steps –The products of the first part are split into three- carbon pyruvate molecules –ATP and NADH form

8. Energy-Requiring Steps 2 ATP invested Energy-Requiring Steps of Glycolysis glucose PGAL P P ADP P ATP glucose-6-phosphate P fructose-6-phosphate ATP fructose1,6-bisphosphate PP ADP Figure 8.4(2) Page 137

9. Energy- Releasing Steps ADP ATP pyruvate ADP ATP pyruvate H2OH2O P PEP H2OH2O P P 2-phosphoglycerate P ADP ATP P 3-phosphoglycerate ADP ATP P 3-phosphoglycerate NAD + NADH PiPi 1,3-bisphosphoglycerate PP NAD + NADH PiPi 1,3-bisphosphoglycerate PP PGAL P P Figure 8.4 Page 137

10. Glycolysis: Net Energy Yield Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP and 2 NADH

11. 8.3 Second Stage Reactions Preparatory reactions –Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide –NAD + is reduced Krebs cycle –The acetyl units are oxidized to carbon dioxide –NAD + and FAD are reduced

12. Preparatory Reactions pyruvate NAD + NADH coenzyme A (CoA) OO carbon dioxide CoA acetyl-CoA

13. Krebs Cycle NAD + NADH =CoA acetyl-CoA oxaloacetatecitrate CoA H2OH2O malateisocitrate H2OH2O H2OH2O FAD FADH 2 fumarate succinate ADP + phosphate group ATP succinyl-CoA OO CoA NAD + NADH OO NAD + NADH  -ketoglutarate Figure 8.6 Page 139

14. The Krebs Cycle Overall Products Coenzyme A 2 CO 2 3 NADH FADH 2 ATP Overall Reactants Acetyl-CoA 3 NAD + FAD ADP and P i

15. Results of the Second Stage All of the carbon molecules in pyruvate end up in carbon dioxide Coenzymes are reduced (they pick up electrons and hydrogen) One molecule of ATP forms Four-carbon oxaloacetate regenerates

16. Coenzyme Reductions during First Two Stages Glycolysis2 NADH Preparatory reactions 2 NADH Krebs cycle 2 FADH 2 + 6 NADH Total 2 FADH 2 + 10 NADH

17. 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 8.4 Electron Transfer Phosphorylation

18. Creating an H + Gradient NADH OUTER COMPARTMENT INNER COMPARTMENT

19. Making ATP: Chemiosmotic Model ATP ADP + P i INNER COMPARTMENT

20. Importance of Oxygen Electron transport phosphorylation requires the presence of oxygen Oxygen withdraws spent electrons from the electron transfer chain, then combines with H + to form water

21. Summary of Energy Harvest (per molecule of glucose) Glycolysis –2 ATP formed by substrate-level phosphorylation Krebs cycle and preparatory reactions –2 ATP formed by substrate-level phosphorylation Electron transport phosphorylation –32 ATP formed

22. Energy Harvest Varies NADH formed in cytoplasm cannot enter mitochondrion It delivers electrons to mitochondrial membrane Membrane proteins shuttle electrons to NAD + or FAD inside mitochondrion Electrons given to FAD yield less ATP than those given to NAD +

23. 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 Efficiency of Aerobic Respiration

24. Do not use oxygen Produce less ATP than aerobic pathways Two types –Fermentation pathways –Anaerobic electron transport 8.5 Anaerobic Pathways

25. 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 +

26. Lactate Fermentation C 6 H 12 O 6 ATP NADH 2 lactate electrons, hydrogen from NADH 2 NAD + 2 2 ADP 2 pyruvate 2 4 energy output energy input GLYCOLYSIS LACTATE FORMATION 2 ATP net

27. Alcoholic Fermentation C 6 H 12 O 6 ATP NADH 2 acetaldehyde electrons, hydrogen from NADH 2 NAD + 2 2 ADP 2 pyruvate 2 4 energy output energy input GLYCOLYSIS ETHANOL FORMATION 2 ATP net 2 ethanol 2 H 2 O 2 CO 2

28. Anaerobic Electron Transport Carried out by certain bacteria Electron transfer chain is in bacterial plasma membrane Final electron acceptor is compound from environment (such as nitrate), not oxygen ATP yield is low

29. FOOD complex carbohydrates simple sugars pyruvate acetyl-CoA glycogenfatsproteins amino acids carbon backbones fatty acids glycerol NH 3 PGAL glucose-6-phosphate GLYCOLYSIS KREBS CYCLE urea Figure 8.11 Page 145 8.6 ALTERNATIVE ENERGY SOURCES

30. 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 Evolution of Metabolic Pathways

31. 8.7 Processes Are Linked sunlight energy water + carbon dioxide PHOTOSYNTHESIS AEROBIC RESPIRATION sugar molecules oxygen In-text figure Page 146