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Chapter 9~ Cellular Respiration: Harvesting Chemical Energy

Chapter 9~ Cellular Respiration: Harvesting Chemical Energy. glucose + oxygen  energy + water + carbon. dioxide. respiration. ATP. +. 6H 2 O. +. 6CO 2. + heat. . C 6 H 12 O 6. +. 6O 2. Harvesting stored energy. Glucose is the model

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Chapter 9~ Cellular Respiration: Harvesting Chemical Energy

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  1. Chapter 9~ Cellular Respiration: Harvesting Chemical Energy

  2. glucose + oxygen  energy + water + carbon dioxide respiration ATP + 6H2O + 6CO2 + heat  C6H12O6 + 6O2 Harvesting stored energy • Glucose is the model • catabolism of glucose to produce ATP

  3. Catabolic pathway • When two molecules are broken down and their energy is released • Two types • Fermentation • Cellular respiration

  4. Cellular respiration is identified as an oxidation-reduction reaction (redox) • Electrons are transferred from one reactant to another • The loss of electrons from the reactant is oxidation • The gain of electrons from a reactant is reduction

  5. oxidation  C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction Coupling oxidation & reduction • REDOX reactions in respiration • release energy as breakdown organic molecules • break C-C bonds • strip off electrons from C-H bonds by removing H atoms • C6H12O6 CO2 =thefuel has been oxidized • electrons attracted to more electronegative atoms • O2 H2O =oxygen has been reduced • couple REDOX reactions & use the released energy to synthesize ATP

  6. oxidation  C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction Oxidation & reduction • Oxidation • adding O • removing H • loss of electrons • releases energy • exergonic • Reduction • removing O • adding H • gain of electrons • stores energy • endergonic

  7. Cellular respiration: overview • (anaerobic) • 1.Glycolysis:cytosol; degrades glucose into pyruvate • (aerobic) • Pyruvate oxidation • 2.Kreb’s Cycle: mitochondrial matrix; pyruvate into carbon dioxide • 3.Electron Transport Chain: inner membrane of mitochondrion; electrons passed to oxygen

  8. glucose      pyruvate 6C 3C 2x Glycolysis • Breaking down glucose • “glyco – lysis” (splitting sugar) • ancient pathway which harvests energy • where energy transfer first evolved( all cells used glycolysis) • transfer energy from organic molecules to ATP • still is starting point for ALL cellular respiration • but it’s inefficient • generate only2 ATP for every 1 glucose • occurs in cytosol

  9. glucose      pyruvate 6C 3C 2x pyruvate       CO2 Glycolysis is only the start • Glycolysis • Pyruvate has more energy to yield • 3 more C to strip off (to oxidize) • if O2 is available, pyruvate enters mitochondria • enzymes of Krebs cycle complete the full oxidation of sugar to CO2 3C 1C

  10. [ ] 2x pyruvate  acetyl CoA + CO2 Oxidation of pyruvate • Pyruvate enters mitochondrial matrix • 3 step oxidation process • releases 2 CO2(count the carbons!) • reduces 2NAD  2 NADH (moves e-) • produces 2acetyl CoA • Acetyl CoA enters Krebs cycle

  11. Krebs cycle 1937 | 1953 • aka Citric Acid Cycle • in mitochondrial matrix • Each turn of the cycle requires one Acetyl CoA • It takes two turns before glucose is oxidized • One turn results in • 2CO2, 3NADH, 1 FADH and 1ATP • But because the cycle takes two pyruvates we double all those numbers Hans Krebs 1900-1981

  12. 2C 6C 5C 4C 3C 4C 4C 4C 4C 6C CO2 CO2 Count the carbons! pyruvate acetyl CoA citrate oxidationof sugars This happens twice for each glucose molecule x2

  13. 2C 6C 5C 4C 3C 4C 6C 4C 4C 4C NADH ATP CO2 CO2 CO2 NADH NADH FADH2 NADH Count the electron carriers! pyruvate acetyl CoA citrate reductionof electroncarriers This happens twice for each glucose molecule x2

  14. So we fully oxidized glucose C6H12O6  CO2 & ended up with 4 ATP!

  15. H+ H+ H+ H+ H+ H+ H+ H+ H+ Electron Carriers = Hydrogen Carriers • Krebs cycle produces large quantities of electron carriers • NADH • FADH2 • go to Electron Transport Chain! ADP+ Pi ATP What’s so important about electron carriers?

  16. 4 NAD+1 FAD 4 NADH+1FADH2 2x 1C 3x 1 ADP 1 ATP Energy accounting of Krebs cycle Net gain = 2 ATP = 8 NADH + 2 FADH2 pyruvate          CO2 3C ATP

  17. Value of Krebs cycle? • If the yield is only 2 ATP then how was the Krebs cycle an adaptation? • value of NADH & FADH2 • electron carriers & H carriers • reduced molecules move electrons • reduced molecules move H+ ions • to be used in the Electron Transport Chain like $$in the bank

  18. ATP accounting so far… • Glycolysis 2ATP • Kreb’s cycle 2ATP • Life takes a lot of energy to run, need to extract more energy than 4 ATP! There’s got to be a better way! A working muscle recycles over 10 million ATPs per second

  19. There is a better way! • Electron Transport Chain • series of proteins built into inner mitochondrial membrane • transport proteins& enzymes • transport of electrons down ETC linked to pumping of H+ to create H+ gradient • yields ~36 ATP from 1 glucose! • only in presence of O2 (aerobic respiration)

  20. e p 1 2 Electron Transport Chain Building proton gradient! NADH  NAD+ + H intermembranespace H+ H+ H+ innermitochondrialmembrane H  e- + H+ C e– Q e– H e– FADH2 FAD H NADH 2H+ + O2 H2O NAD+ cytochromebc complex cytochrome coxidase complex NADH dehydrogenase mitochondrialmatrix What powers the proton (H+) pumps?…

  21. Electrons flow downhill • Electrons move in steps from carrier to carrier downhill to oxygen • each carrier more electronegative • controlled oxidation • controlled release of energy

  22. Chemiosmosis • The diffusion of ions across a membrane • build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis So that’sthe point!

  23. Peter Mitchell 1961 | 1978 • Proposed chemiosmotic hypothesis • revolutionary idea at the time proton motive force 1920-1992

  24. The electron transport chain and chemiosmosis are called oxidative phosphorylation • Oxygen is necessary • ADP is phosphorylated Total yield per glucose molecule of cellular respiration is between 36 and 38 ATP ETC or oxidative phosphorylation yields 32 to 34 of that total

  25. Review: Cellular Respiration • Glycolysis: 2 ATP (substrate-level phosphorylation) • Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) • Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2NADH (acetyl CoA) = 6ATP 6NADH (Kreb’s) = 18 ATP 2FADH2 (Kreb’s) = 4 ATP • 38 TOTAL ATP/glucose

  26. pyruvate  ethanol + CO2 3C 2C 1C pyruvate  lactic acid NADH NADH NAD+ NAD+ 3C 3C Fermentation (anaerobic) • Bacteria, yeast back to glycolysis • beer, wine, bread • Animals, some fungi back to glycolysis • cheese, anaerobic exercise (no O2)

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