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Chapter 8

Chapter 8. How Cells Release Chemical Energy. Metabolic reactions. Photosynthesis Light energy converted into stored energy (glucose) CO 2 + H 2 O => C 6 H 12 O 6 (glucose) + O 2 Endergonic Cellular Respiration Stored energy (glucose) converted into useable energy (ATP)

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Chapter 8

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  1. Chapter 8 How Cells Release Chemical Energy

  2. Metabolic reactions • Photosynthesis • Light energy converted into stored energy (glucose) • CO2 + H2O => C6H12O6 (glucose) + O2 • Endergonic • Cellular Respiration • Stored energy (glucose) converted into useable energy (ATP) • C6H12O6 (glucose) + O2 => CO2 + H2O • Exergonic

  3. Cellular respiration • Aerobic Respiration • Requires oxygen • High energy (ATP) yield • Glycolysis—cytoplasm • Kreb’s Cycle—mitochondrial matrix • Electron Transport System—cristae • Anaerobic Respiration • Doesn’t require oxygen • Organisms without mitochondria • Low energy yield

  4. Aerobic respiration • Step 1—Glycolysis • Glucose (6C) broken down into two PGAL (3C) • PGAL restructured into pyruvate • Produces 2 NADH • Requires 2 ATP to start • Produces 4 ATP • Net gain of 2 ATP • Glucose  P-Glucose  2 Pyruvate

  5. Aerobic respiration • Step 2a—Acetyl-CoA • Pyruvate (3C) combines with CoA • Releases CO2 • NAD+ NADH • Forms acetyle-CoA (2C) • 2 Pyruvate => 2 CO2 + 2 NADH

  6. Aerobic respiration • Step 2b—Krebs Cycle • 2 Acetyl-CoA enter • Transfers carbons to oxaloacetate (C4), forming citrate (C6) • Cycles through steps to rearrange citrate • 2 CO2 released • Ends forming oxaloacetate • Cycle starts again • Net gain of 4 CO2, 6 NADH, 2 FADH2, 2 ATP

  7. Aerobic respiration • Step 3—Electron Transfer Phosphorylation • NADH & FADH2 from previous steps start chain • Electrons flow through “chain” of membrane proteins • Each protein then takes H+ from above molecules and pumps them into intermembrane space • This sets up concentration gradient • H+ moves down gradient through ATP synthase • Movement forms ATP from ADP & P (32 net gain) • Ends with electrons passed to O2, combines with H+ to form H2O

  8. Aerobic respiration • If no oxygen, electrons can’t pass on • This backs up to NADPH, so no H+ gradients • No ATP forms, starving cells

  9. Aerobic respiration • Glycolysis • Glucose + 2ATP  4ATP + 2NADH + 2 Pyruvate • Intermediate • 2 Pyruvate  2CO2 + 2NADH + 2 Acetyl-CoA • Krebs Cycle • 2 Acetyl-CoA 6NADH + 2ATP + 2FADH2 • Electron Transfer • 10NADH + 2FADH2 32ATP + 4CO2 + 6H2O • C6H12O6 + 6O2 6H2O + 6CO2 + 36 ATP + heat

  10. Anaerobic respiration • Fermenters • Protists, bacteria • Marshes, bogs, deep sea, animal gut, sewage, canned food • Some die when exposed to O2 • Some indifferent to O2 • Some can use O2, but switch to fermentation when none around

  11. Anaerobic respiration • Glycolysis happens normally • 2 Pyruvate, 2 NADH, 2 Net ATP form • Enough energy for many single-celled species • Not enough energy for large organisms

  12. Alcohol fermentation • Glucose  2 Pyruvate  2 Acetaldehyde + 2 CO2 • NADH + Acetaldehyde  Ethanol

  13. Alcohol fermentation • Yeasts • Bread • Beer • Wine

  14. Lactate Fermentation • Glucose  Pyruvate  Lactate

  15. Lactate fermentation • Can spoil food • Some bacteria create food • Cheese, yogurt, buttermilk • Cure meats • Pickle some fruits & vegetables

  16. Lactate fermentation • Muscle cells • Slow-twitch—light, steady, prolonged activity • Marathons, bird migrations • Many mitochondria • Only aerobic respiration • “dark” meat in birds • Fast-twitch—immediate, intense energy • Weight lifting, sprinting • Few mitochondria • Lactate fermentation • Produce ATP quickly, but not for long • “white” meat in birds

  17. Energy storage • Glucose absorbed through intestines • When glucose level rises, glucose converted to glycogen • Diverts at glucose-6-phosphate in glycolysis

  18. Energy storage • Glycogen is storage polysaccharide • Stores in liver & muscles • With low blood glucose, insulin released • This triggers glycogen to convert back to glucose • If too many carbohydrates/glucose in blood, acetyl-CoA diverted & made into fatty acid

  19. Using fats • Body stores most fats as triglycerides • When glucose levels fall, triglycerides used • Enzymes remove glycerol

  20. Using fats • Glycerol converted to PGAL • PGAL converted to pyruvate as in glycolysis

  21. Using proteins • Happens when eat too many proteins, or when carbohydrates & fats used • Enzymes break down protein molecules • Ammonia (NH3) removed • Leftover carbon backbone split • Forms acetyl-CoA, pyruvate, or intermediate of Krebs cycle • Specific amino acid determines which is formed

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