How Cells Release Chemical Energy

1. How Cells Release Chemical Energy Chapter 6

2. Main Types of Energy-Releasing Pathways Anaerobic pathways • Evolved first • Don’t require oxygen • All reactions take place in the cytoplasm Aerobic pathways • Evolved later • Requires oxygen • Reactions start in the cytoplasm and finish in the mitochondria

3. Summary Equation for Aerobic Respiration C6H12O6 + 6O2 6CO2 + 6H2O + ATP GLUCOSE OXYGEN WATER CARBON DIOXIDE

5. 3 Steps of Aerobic Respiration Glycolysis --- Uses: Glucose, 2 ATP, 2 NAD+ --- Makes: 2 Pyruvate, 4 ATP, 2 NADH Krebs Cycle ---Uses: 2 Pyruvate, 6 NAD+, 2 FAD ---Makes: 6 CO2, 2 ATP, 6 NADH, 2 FADH2

6. Glycolysis: Net Energy Yield Energy requiring steps: 2 ATP used Energy releasing steps: 2 NADH formed 4 ATP formed Net yield: 2 ATP + 2 NADH

7. Mitochondria

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

9. ATP O O =CoA Krebs Cycle acetyl-CoA CoA oxaloacetate citrate H2O NADH NAD+ H2O Mitochondrion's Inner Compartment malate isocitrate NAD+ H2O O O NADH fumarate FADH2 a-ketoglutarate FAD NAD+ CoA NADH succinate succinyl-CoA ADP + phosphate group

10. Results of the Second Stage • All of the carbon molecules in pyruvate eventually are released as Carbon Dioxide • Coenzymes pick up hydrogens and electrons • 2 ATP are formed

11. Coenzyme Reductions During First Two Stages • Glycolysis 2 NADH • Preparatory reactions 2 NADH • Krebs cycle 2 FADH2 + 6 NADH • Total 2 FADH2 + 10 NADH

12. Electron Transfer Phosphorylation • Occurs in Mitochondria • Coenzymes deliver electrons to electron transfer systems • Sets up H+ ion gradients • Gradients powers ATP formation • Requires Oxygen

13. glucose ATP 2 2 NAD+ 2 PGAL ATP 4 2 NADH 2 pyruvate Glycolysis 2 FADH2 2 CO2 e– 2 acetyl-CoA oxygen accepts “spent” electrons 2 NADH H+ H+ 6 NADH 2 ATP Krebs Cycle ATP H+ 2 FADH2 ATP H+ 4CO2 ATP 32 H+ H+ ADP + Pi Electron Transfer phosphorylation H+ H+ H+ Fig. 6-5 p.87

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

15. Fermentation Pathways • Begin with glycolysis • Are anaerobic: don’t require oxygen • Yield only 2 ATP from glycolysis • Steps after glycolysis only regenerate NAD+

16. GLYCOLYSIS Alcoholic Fermentation C6H12O6 2 ATP 2 NAD+ energy input 2 ADP NADH 2 ATP 4 2 pyruvate energy output 2 ATP net ETHANOL FORMATION 2 H2O 2 CO2 2 acetaldehyde electrons, hydrogen from NADH 2 ethanol

17. Lactate Fermentation GLYCOLYSIS C6H12O6 ATP 2 energy input 2 NAD+ 2 ADP NADH 2 ATP 4 2 pyruvate energy output 2 ATP net LACTATE FORMATION electrons, hydrogen from NADH 2 lactate

18. sunlight energy photosynthesis organic compounds, oxygen carbon dioxide, water aerobic respiration p.92

19. Importance of Insulin • Insulin is a __________ released by the pancreas when there is a high concentration of glucose in the blood. • It binds to cell receptors and tells the cells to take in glucose and start glycolysis.

20. Diabetes • Type 1: (Juvenile onset) – Disease or condition prevents the pancreas from releasing insulin. (Treated by injecting insulin before meals) Type 2 (adult onset) – Cell receptors start to become insensitive to insulin. (treated by exorcise, weight loss, and some drugs)