Cellular Respiration - Oxidative Phosphorylation

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  • Cellular Respiration - Oxidative Phosphorylation

    1. 1. Cellular RespirationPart 3: Electron Shuttles, ETC & Chemiosmosis
    2. 2. Recall: Location Glycolysis occurs in the cytoplasm Electron transport chain (ETC) starts in the mitochondrial matrix The NADH produced during glycolysis must make its way into the mitochondria
    3. 3. Electron Shuttle
    4. 4. Electron Shuttle NADH produced in glycolysis must be transported from the cytoplasm into the mitochondria to enter the ETC. Mitchondria is not permeable to NADH produced in the cytoplasm Shuttling of NADH is indirectTwo shuttle mechanisms: glycerol phosphate shuttle malate-aspartate shuttle
    5. 5. Glycerol Phosphate Shuttle In brain tissue and skeletal muscle tissue Results in FADH2 in the matrix 2e- from NADH get shuttled into the mitochondria and become part of FAD to become FADH2 CYTOPLASM INTERMEMBRANE MATRIX SPACE NADH DHAP DHAP FADH2 ETC NAD+ Glycerol 3- Glycerol 3- FAD phosphate phosphate
    6. 6. Malate-Aspartate Shuttle In liver, kidney, heart Results in NADH in the matrix 2e- from NADH get shuttled into the mitochondria and become part of NAD+ to become NADH CYTOPLASM β INTERMEMBRANE MATRIX SPACE Aspartate Aspartate NADH Oxaloacetate Oxaloacetate NADH ETC NAD+ Malate Malate NAD+
    7. 7. Two Methods of ATP Synthesis
    8. 8. Two Methods of ATP SynthesisSubstrate-level phosphorylation direct ATP formation through phosphate transfer from substrate to ADP Occurs in glycolysis & Kreb cycleOxidative phosphorylation indirect ATP formation through redox reactions involving O2 as a final electron acceptor Driven by the electron transport chain
    9. 9. Substrate-level Phosphorylation enzyme transfers a phosphate group from a substrate molecule to ADP rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation Enzyme Enzyme ADP P Substrate + ATPFigure 9.7 Product
    10. 10. Oxidative Phosphorylation Involves 2 processes that occur on the inner mitochondrial membrane (IMM) Electron Transport Chain:  Energy in electrons of NADH and FADH2 used to drive H+ against its concentration gradient  Electrons fall to oxygen (final electron acceptor) Chemiosmosis:  Using facilitated diffusion of H+ to drive the synthesis of ATP
    11. 11. Electron Transport ChainOverview The ETC removes energy stored in the NADH and FADH2 molecules to:  Move protons against its concentration gradient creating a proton gradient across the inner mitochondrial membrane (IMM)  Final electron acceptor is oxygen which converts H2O All reactions are redox reactions
    12. 12. Electron Transport Chain (ETC) Made of electron carrier molecules embedded in the inner membrane of mitochondria Most carriers are protein molecules except for ubiquinone (Q)
    13. 13. ETC Thermodynamics  Each electron transfer step is energetically favourable  Each carrier in the chain has a higher electronegativity than the carrier before it  Electrons from NADH and FADH2 lose energy (pulled downhill) by each electron carrier
    14. 14. ETC & Oxygen NADH 50 Final electron acceptor is FADH2 the very electronegative 40 FMN Fe•S I FAD Fe•S II Multiprotein complexes oxygen Free energy (G) relative to O2 (kcl/mol) O III Cyt b Oxygen drives the redox 30 Fe•S Cyt c1 IV reactions Cyt c Cyt a Cyt a3 Lack of oxygen prevents 20 this whole process from 10 occurring 0 2 H + + 1⁄2 O2 H2O
    15. 15. ETC & Chemiosmosis Overview Inner Mitochondrial Glycolysis Oxidative phosphorylation. membrane electron transport and chemiosmosis ATP ATP ATP H+ H+ H+ H+ Cyt c Protein complexIntermembrane of electronspace carners Q IV I III ATPInner II synthasemitochondrial FADH2 H2Omembrane FAD+ 2 H+ + 1/2 O2 NADH+ NAD+ ADP + Pi ATP (Carrying electrons from, food) H+Mitochondrial Chemiosmosis Electron transport chainmatrix Electron transport and pumping of protons (H+), ATP synthesis powered by the flow which create an H+ gradient across the membrane Of H+ back across the membraneFigure 9.15 Oxidative phosphorylation
    16. 16. ETC Components: Complex I  2 e- from NADH are transferred to Complex I  Protons are pumped across the inner mitochondrial membrane (IMM) by Complex I
    17. 17. ETC Components: Q  e- are transferred from Complex I to ubiquinone (Q)  Q is lipid soluble  can move within the phospholipid bilayer  mobile component within the IMM
    18. 18. ETC Components: Complex III  e- are transferred from Q to Complex III  Protons are pumped across the IMM by Complex III
    19. 19. ETC Components: Cyt C  e- are transferred from Complex III to cytochrome c (cyt c)  cyt c is a mobile component on the surface of IMM (peripheral), in the intermembrane space
    20. 20. ETC Components: Complex IV  e- are transferred from cyt c to Complex IV  Protons are pumped across the IMM by Complex IV
    21. 21. ETC Components: O2  O2 is the final electron acceptor of the ETC  enough e- pass through the ETC to produce full H2O molecules
    22. 22. FADH2 Pathway Inner Mitochondrial Glycolysis Oxidative phosphorylation. membrane electron transport and chemiosmosis ATP ATP ATP H+ H+ H+ H+ Cyt cIntermembrane Xspace Q IV I III ATPInner II synthasemitochondrial FADH2 H2Omembrane FAD+ 2 H+ + 1/2 O2 ADP + Pi ATPMitochondrialmatrix H+ Figure 9.15
    23. 23. ETC Components: Complex II  2e- are transferred from FADH2 to Complex II Q  no protons are pumped across the IMMComplex II  e- are transferred from FADH2 Complex II to Q and FAD+ proceed through the rest of ETC
    24. 24. ETC Components: Complex II Inner Mitochondrial Glycolysis Oxidative phosphorylation. membrane electron transport and chemiosmosis ATP ATP ATP H+ H + H+ H+ Cyt c Protein complexIntermembrane of electronspace carners Q IV I III ATPInner II synthasemitochondrial FADH2 H2Omembrane FAD+ 2 H+ + 1/2 O2 NADH+ NAD+ ADP + Pi ATP (Carrying electrons from, food) H+Mitochondrial Chemiosmosis Electron transport chainmatrix Electron transport and pumping of protons (H ), + ATP synthesis powered by the flow which create an H+ gradient across the membrane Of H+ back across the membraneFigure 9.15 Oxidative phosphorylation
    25. 25. Electrochemical Proton Gradient High H+ Low H+
    26. 26. ETC Summary NADH e- transferred to O2; three proton pumps activated FADH2 e- transferred to O2; two proton pumps activated electrochemical proton gradient formed across IMM
    27. 27. Electron Transport Chain  NADH is oxidized and FMN (complex I) is reduced NADH ↓ 50  FMN is oxidized as it passes electrons to an iron FADH2 sulfur protein, FeS (complex I). 40 FMN I FAD Multiprotein complexes ↓ FeS is oxidized as it pass electrons toFree energy (G) relative to O2 (kcl/mol) Fe•S Fe•S II  O 30 Cyt b Fe•S III ubiquinone Q. FADH2 enters at complex II to Q, Cyt c1 IV bypassing complex I. ↓ Cyt c Cyt a Q passes electrons on to a succession of Cyt a3 20  electron carriers (in complex III and IV), most of 10 which are cytochromes. ↓  Cyt a3 , the last cytochrome passes electrons to oxygen. 0 2 H + + 1⁄2 O2 Figure 9.13 H2O
    28. 28. Oxidative Phosphorylation High H+ Low H+
    29. 29. Proton Motive Force:Chemiosmosis The electrochemical gradient produced by the ETC:  High proton concentration in the intermembrane space Chemiosmosis: facilitated diffusion of proton down the concentration gradient Oxidative phosphorylation:  Oxidation (ETC) coupled with phosphorylation (ATP synthesis)  Occurs by coupling passive movement of protons to produce ATP through the enzyme complex ATP synthase  ATP is produced as protons flow through ATP synthase
    30. 30. ATP Synthase: Complex V INTERMEMBRANE SPACE H+ A rotor within the membrane spins Fo = rotor H+ H+ H+ clockwise when H+ flows past H+ it down the H+  Transmembrane gradient. H+ H+ A stator anchored  Proton channel in the membrane holds the knob F1 = knob, rod stationary.  Peripheral A rod (for “stalk”) extending into the knob also  catalytic sites that spins, activating catalytic sites in H+ the knob. phosphorylate ADP to ATP Three catalytic sites in the ADP stationary knob + join inorganic Pi ATP Phosphate to ADP to make ATP. MITOCHONDRIAL MATRIX Figure 9.14
    31. 31. ATP Synthase: Complex V
    32. 32. Rotational Catalysis Protons flowing through the F0 component cause the γ subunits in the rod to rotate.  electrochemical gradient translates into mechanical energy When an irregularly shaped γ subunit rotates, it contacts a different β subunit. As a result, the β subunits change conformation, which changes their affinity for ATP.
    33. 33. β subunit Catalytic subunit 3 conformation:  loosely binds ADP and P  tightly binds ADP and Pi to form ATP  releases ATP When the γ interacts closely with the β subunit, ATP is synthesized Each of the 3 β subunits in the F1 component take turn catalyzing the synthesis of ATP
    34. 34. Animation ETC http://www.youtube.com/watch?v=lRlTBRPv6xM&featu Proton Gradient & ATP synthase http://www.youtube.com/watch?v =3y1dO4nNaKY&feature=related ATP synthase http://www.youtube.com/watch?v =PjdPTY1wHdQ&feature=related Cellular Respiration Lecture: http://www.youtube.com/watch?v=qviLDKDJNKM&feat
    35. 35. ATP ProductionIn general: 1 NADH  3 ATP molecules 1 FADH2  2 ATP molecules The ETC is coupled with ATP synthesis. The latter is dependent on the former.
    36. 36. ATP Production Summary Cellular EnergyRespiration Step Molecules ATP Totals Produced Glycolysis 2 ATP 2 ATP 2 NADH 4-6 ATP Oxidative 2 NADH 6 ATPDecarboxylation Krebs Cycle 6 NADH 18 ATP 2 FADH2 4 ATP 2 ATP 2 ATP TOTAL 36-38 ATP
    37. 37. ATP Production Summary Cellular EnergyRespiration Step Molecules ATP Totals Produced Glycolysis 2 ATP 2 ATP 2 NADH 4-6 ATP Oxidative 2 NADH 6 ATPDecarboxylation Krebs Cycle 6 NADH 18 ATP 2 FADH2 4 ATP 2 ATP 2 ATP TOTAL 36-38 ATP
    38. 38. Cellular Respiration Summary Electron shuttles MITOCHONDRIONCYTOSOL 2 NADH span membrane or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Glycolysis Oxidative 2 Citric phosphorylation: 2 Acetyl acid electron transport Glucose Pyruvate CoA cycle and chemiosmosis + 2 ATP + 2 ATP + about 32 or 34 ATP by substrate-level by substrate-level by oxidative phosphorylation, depending phosphorylation phosphorylation on which shuttle transports electrons from NADH in cytosol About Maximum per glucose: 36 or 38 ATPFigure 9.16
    39. 39. Catabolism of various moleculesfrom food Proteins Carbohydrates Fats Amino Sugars Glycerol Fatty acids acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Citric acid cycle Oxidative Figure 9.19 phosphorylation
    40. 40. Regulation of CellularRespiration Glucose AMP Glycolysis Fructose-6-phosphate Stimulates + Phosphofructokinase – – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Citric acid cycle Oxidative Figure 9.20 phosphorylation

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