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Electron Transport Chain

Electron Transport Chain. Thermodynamics of Glucose Oxidation. Glucose + 6 O 2 ——> 6 CO 2 + 6 H 2 O. ∆G o’ = -2866 kJ/mol. Half-Reactions of Glucose Oxidation. Glucose + 6 H 2 O ——> 6 CO 2 + 24 H + + 24 e – 6 O 2 + 24 H + + 24 e – ——> 12 H 2 O. NADH and FADH 2.

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Electron Transport Chain

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  1. Electron Transport Chain

  2. Thermodynamics of Glucose Oxidation Glucose + 6 O2 ——> 6 CO2 + 6 H2O ∆Go’ = -2866 kJ/mol

  3. Half-Reactions of Glucose Oxidation Glucose + 6 H2O ——> 6 CO2 + 24 H+ + 24 e– 6 O2 + 24 H+ + 24 e– ——> 12 H2O NADH and FADH2

  4. Sites of NADH and FADH2 Formation

  5. Sites of NADH and FADH2 Formation

  6. Mitochondrial Electron Transport Chain System of Linked Electron Carriers

  7. Components of Electron Transport Process • Reoxidation of NADH and FADH2 • Sequential oxidation-reduction of multiple redox centers (four enzyme complexes) • Production of proton gradient across the mitochondrial membrane

  8. Oxidative Phosphorylation Synthesis of ATP driven by free energy of electrochemical gradient

  9. Coupling of Electron Transport and ATP Synthesis NOTE: ATP Synthesis in the Mitochondrion

  10. The Mitochondrion • Prokaryotic origin • Double membrane bound • Genome • Human: encodes 13 genes, all ETC subunits.

  11. Mitochondrial Outer Membrane Permeable to molecules smaller than ~5 kD

  12. X-Ray Structure of E. coli OmpF Porin Figure 9-23a

  13. X-Ray Structure of E. coli OmpF Porin Trimer Figure 9-23b

  14. Mitochondrial Intermembrane Space (IMS)[Metabolites] = Cytosolic ConcentrationLocalized Compartmentation of H+

  15. Mitochondrial Inner Membrane(Permeability Barrier)Transport

  16. Types of Transport • Nonmediated Transport (Diffusion) • H2O; O2; CO2 • Mediated Transport • Passive-mediated Transport(facilitated diffusion) • Active Transport • Facilitated by Proteins: • Carriers, Transporters, Translocases, or Permeases.

  17. Kinetic Properties of Mediated Transport • Saturation kinetics • Speed and specificity • Susceptibility to competitive inhibition • Susceptibility to chemical inactivation

  18. Stoichiometry of Mediated Transport

  19. Entry of “NADH” into Mitochondria No NADH Transporter

  20. Malate–Aspartate Shuttle

  21. Malate–Aspartate Shuttle

  22. Glycerophosphate Shuttle

  23. Transport of ADP, ATP, and Inorganic Phosphate (Pi)

  24. ADP-ATP Translocator ADP/ATP Exchanger Driven by electrochemical gradient

  25. Phosphate Transport Driven by ∆pH

  26. Phosphate Transporter H+(out) H2PO4–(out) H+(in) H2PO4–(in)

  27. Electron Transport Electron Transport is an Exergonic Process

  28. Standard Reduction Potentials

  29. Standard Reduction Potential Difference ∆Eo’ = Eo’(e–acceptor)– Eo’(e–donor) ∆Go’ = –nF∆Eo’ For negative G need positive E E(acceptor) > E(donor) Note: reduction potential is extremely pH sensitive E = Eo’ + 0.06V*(7-pH)

  30. What is the ∆Eo’ and ∆Go’ for the Oxidation of NADH by O2?

  31. Electron Carriers Operate in Sequence

  32. Electron Transport Complexes • Complex I: NADH–Coenzyme Q Oxidoreductase • Complex II: Succinate–Coenzyme Q Oxidoreductase • Complex III: Coenzyme Q–Cytochrome c Oxidoreductase • Complex IV: Cytochrome c Oxidase

  33. Overview of Electron Transport in the Mitochondrion

  34. Mobile Electron Carriers Coenzyme Q Cytochrome c

  35. Coenzyme Q

  36. Oxidation States of Coenzyme Q

  37. Cytochromes Electron Transport Heme Proteins Fe3+ + e– ——> Fe2+

  38. b c a Hemes Note: isoprene side chain Iron-Protoporphyrin IX Like Mb and Hb Note: Thioether Links

  39. Cytochrome Spectra

  40. Complex I(NADH–Coenzyme Q Oxidoreductase) Accepts Electrons from NADH NADH + CoQ(oxidized) ——> NAD+ + CoQ(reduced) Protons translocated 4H+(Matrix) ——> 4H+(IMS)

  41. Coenzymes of Complex I(Flavin Mononucleotide, FMN)Oxidation states like FAD

  42. Coenzymes of Complex I(Iron-Sulfur Clusters) One-electron oxidation-reduction Conjugated System (Fe between +2 and +3)

  43. Thermodynamics of Complex I

  44. Hydrophilic Domain of Complex I from Thermus thermophilis ~ matrix ~ cytoplasm Electrons follow a multistep path

  45. Structure of Bacteriorhodopsin Figure 9-22

  46. Proton Wire • Deprotonation of Schiff base and protonation of Asp 85 • Proton release to the extracellular surface • Reprotonation of the Schiff base and deprotonation of Asp 96 • Reprotonation of Asp 96 from the cytoplasmic surface • Deprotonation of Asp 85 and reprotonation of the proton release site

  47. Complex II(Succinate–Coenzyme Q Oxidoreductase) Contributes Electrons to Coenzyme Q Succinate + CoQ(oxidized) ——> Fumarate + CoQ(reduced) Does not pump protons

  48. Composition of Complex II • Succinate Dehydrogenase • FAD • [4Fe-4S] cluster • [3Fe-4S] cluster • [2Fe-2S] cluster • Cytochrome b560

  49. Thermodynamics of Complex II

  50. E. coli Complex II Cytoplasm ~matrix Plasma Membrane ~IM Periplasm ~cytoplasm

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