Oxidative Phosphorylation


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Involves the elctron transport chain and chemiosmosis in the mitochondrial inner membrane

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Oxidative Phosphorylation

  1. 1. 3. Oxidative Phosphorylation <ul><li>Occurs in cristae- inner membrane of the mitochondria </li></ul><ul><li>The surface area of the membrane allows for thousands of copies of the electron transport chain </li></ul><ul><li>Electron Transport Chain- multiprotein complex number I – IV </li></ul><ul><li>Prosthetic groups (non-protein compounds) are tightly bound to the proteins and help with enzymatic activities. </li></ul><ul><li>NADH reaches complex I (FMN and iron-sulfur protein Fe-S) </li></ul><ul><li>NADH is oxidized by flavoprotein (FMN) name due to its flavin prosthetic group- FMN is reduced </li></ul><ul><li>FMN is oxidized as it passes the e- to Fe-S in complex I; Fe-S is reduced. </li></ul><ul><li>Fe-S is oxidized as it passes the e- to ubiquinone Q, a hydrophobic molecule and the only non-protein in the series. </li></ul><ul><li>Between Q and Oxygen lies a series of proteins called cytochromes . Their prosthetic group is called a heme group which has an iron that accepts and donates the e- </li></ul>
  2. 2. Oxidative Phosphorylation cont. <ul><li>The last cytochrome to receive the e- before the oxygen is cyt a 3 </li></ul><ul><li>The oxygen is extremely electronegative and accepts the e- from cyt a 3 </li></ul><ul><li>Each oxygen also picks op a pair of H+ from the aqueous solution surrounding the mitochondria; forming water. </li></ul><ul><li>FADH 2 adds it e- to complex II, at a lower energy level than NADH. </li></ul>
  3. 3. Chemiosmosis <ul><li>An energy-coupling mechanism that uses stored energy in the form of H+ gradient across the membrane to drive cellular work. </li></ul><ul><li>Populating the mitochondrion in conjunction with the ETC is ATP Synthase- an enzyme that catalyzes the production of ATP from ADP </li></ul><ul><li>ATP Synthase uses the energy of an existing ion gradient across the membrane to power ATP synthesis </li></ul><ul><li>The ion gradient is of hydrogen ions (H+) across the mitochondrion membrane; a concentration difference of H+ ions across the membrane </li></ul><ul><li>Osmosis here is referred to as the flow of H+ across the membrane </li></ul><ul><li>ATP synthase- a multisubunit complex of 4 main parts- each of multiple polypeptides </li></ul><ul><ul><li>A rotor in the inner mitochondrial membrane </li></ul></ul><ul><ul><li>A knob that goes into the mitochondrial matrix </li></ul></ul><ul><ul><li>Internal rod extending from the rotor into the knob </li></ul></ul><ul><ul><li>A stator that holds the knob stationary </li></ul></ul><ul><li>A H+ goes in between the stator and the rotor which rotates the rotor </li></ul>
  4. 4. Chemiosmosis cont. <ul><li>The spinning rod activates catalytic reactions that combines inorganic phosphate to ADP to form ATP </li></ul><ul><li>The H+ gradient was generated by the releasing of the e- during the ETC. </li></ul><ul><li>This results in a proton motive force </li></ul><ul><li>The proton motive force drives H+ across the membrane </li></ul><ul><li>Where else does this proton motive force exist? </li></ul><ul><li>Chloroplasts- instead of organic compounds, light is used to drive ATP synthesis </li></ul><ul><li>Prokaryotes- lack both mitochondria and chloroplasts but uses this gradient to move nutrients across the membrane, move flagella, synthesis ATP </li></ul>
  5. 5. <ul><li>At the end of the chain </li></ul><ul><ul><li>Electrons are passed to oxygen, forming water </li></ul></ul>H 2 O O 2 NADH FADH2 FMN Fe•S Fe•S Fe•S O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H + + 1  2 I II III IV Multiprotein complexes 0 10 20 30 40 50 Free energy ( G ) relative to O 2 (kcl/mol) Figure 9.13
  6. 6. <ul><li>Glycolysis consists of two major phases </li></ul><ul><ul><li>Energy investment phase </li></ul></ul><ul><ul><li>Energy payoff phase </li></ul></ul>Glycolysis Citric acid cycle Oxidative phosphorylation ATP ATP ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 P 2 NAD + + 4 e - + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2 NAD + + 4 e – + 4 H + 2 NADH + 2 H + Figure 9.8
  7. 7. Chemiosmosis: The Energy-Coupling Mechanism <ul><li>ATP synthase </li></ul><ul><ul><li>Is the enzyme that actually makes ATP </li></ul></ul>INTERMEMBRANE SPACE H + H + H + H + H + H + H + H + P i + ADP ATP A rotor within the membrane spins clockwise when H + flows past it down the H + gradient. A stator anchored in the membrane holds the knob stationary. A rod (for “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. MITOCHONDRIAL MATRIX Figure 9.14
  8. 8. <ul><li>Chemiosmosis and the electron transport chain </li></ul>Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP Inner Mitochondrial membrane H + H + H + H + H + ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H + + 1 / 2 O 2 H 2 O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15
  9. 9. Overview <ul><li>There are three main processes in this metabolic enterprise </li></ul>Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH 2 2 NADH 6 NADH 2 FADH 2 2 NADH Glycolysis Glucose 2 Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Maximum per glucose: About 36 or 38 ATP + 2 ATP + 2 ATP + about 32 or 34 ATP or Figure 9.16
  10. 10. Anaerobic Pathway of Glycolysis 2 ADP + 2 P 1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 P 1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Lactate (b) Lactic acid fermentation H H OH CH 3 C O – O C C O CH 3 H C O CH 3 O – C O C O CH 3 O C O C OH H CH 3 CO 2 2 Figure 9.17
  11. 11. Overview <ul><li>Pyruvate is a key juncture in catabolism </li></ul>Glucose CYTOSOL Pyruvate No O 2 present Fermentation O 2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18
  12. 12. Carbohydrates not only source of Energy Use <ul><li>The catabolism of various molecules from food </li></ul>Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH 3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19
  13. 13. Regulation of Cellular Respiration <ul><li>Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle </li></ul><ul><li>Controlled by feedback mechanisms </li></ul>Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + – – Figure 9.20