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2.) Mitochondrial respiratory chain and oxidative phosphorylation

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  1. Front
    Oxidative phosphorylation
    Back
    Process in which energy from electron transfer is used to make ATP from ADP + Pi in the inner mitochondrial membrane
  2. Front
    Main electron donors for oxidative phosphorylation
    Back
    NADH and FADH2
  3. Front
    Sources of NADH and FADH2 for oxidative phosphorylation
    Back
    Glycolysis, pyruvate dehydrogenase, TCA cycle, and fatty acid oxidation
  4. Front
    Respiratory chain
    Back
    Ordered chain of electron carriers that transfers electrons to oxygen
  5. Front
    Final electron acceptor in the respiratory chain
    Back
    Oxygen
  6. Front
    Product formed when oxygen accepts electrons in the respiratory chain
    Back
    Water
  7. Front
    Complexes that pump protons in the respiratory chain
    Back
    Complexes I, III, and IV
  8. Front
    Direction of proton pumping in oxidative phosphorylation
    Back
    From the matrix to the intermembrane space
  9. Front
    What creates the proton gradient in oxidative phosphorylation
    Back
    Proton pumping by Complexes I, III, and IV during electron transport
  10. Front
    How ATP synthase is driven
    Back
    Protons flow back into the matrix through ATP synthase
  11. Front
    Chemiosmotic theory
    Back
    The proton gradient generated by electron transport drives ATP synthesis through ATP synthase
  12. Front
    Outer mitochondrial membrane
    Back
    Relatively permeable membrane containing porin channels
  13. Front
    Reason the outer mitochondrial membrane is relatively permeable
    Back
    Presence of porin channels
  14. Front
    Inner mitochondrial membrane
    Back
    Impermeable to most small molecules and ions, including H+
  15. Front
    Major components of the inner mitochondrial membrane
    Back
    Respiratory chain, ATP synthase, and many transporters
  16. Front
    Matrix mitochondrial enzymes
    Back
    Enzymes of pyruvate oxidation, TCA cycle, and fatty acid oxidation
  17. Front
    Consequence if the inner mitochondrial membrane were freely permeable to H+
    Back
    Oxidative phosphorylation would fail because the proton gradient could not be maintained
  18. Front
    Electron flow from NADH
    Back
    NADH → FMN → Fe-S → CoQ → Complex III (cyt b → cyt c1) → cytochrome c → Complex IV (cyt a, cyt a3, Cu) → O2
  19. Front
    Electron flow from FADH2
    Back
    FADH2 → Complex II → CoQ → Complex III → cytochrome c → Complex IV → O2
  20. Front
    Why FADH2 electrons skip Complex I
    Back
    They enter the respiratory chain at Complex II
  21. Front
    Why electron flow in the respiratory chain is one-way
    Back
    Electrons move according to increasing reduction potential toward carriers with more positive E0′
  22. Front
    Reason oxygen is the final electron acceptor
    Back
    Oxygen has the strongest tendency to accept electrons
  23. Front
    Order of reduction potentials in the lecture
    Back
    NADH < FMN < CoQ < cyt b < cyt c1 < cyt c < cyt a < cyt a3 < O2
  24. Front
    NADH as an electron carrier
    Back
    Diffusible electron carrier that donates 2 electrons to Complex I
  25. Front
    FMN and FAD
    Back
    Flavin electron carriers that can carry 1 or 2 electrons and are tightly bound to enzymes
  26. Front
    Fe-S centers
    Back
    One-electron carriers found in Complexes I, II, and III
  27. Front
    Coenzyme Q (ubiquinone, CoQ)
    Back
    Lipid-soluble mobile carrier that diffuses in the inner mitochondrial membrane and accepts both electrons and protons
  28. Front
    Function of CoQ
    Back
    Collects electrons from different sources and transfers them within the inner mitochondrial membrane
  29. Front
    Cytochromes
    Back
    Heme proteins that carry electrons via Fe3+/Fe2+ cycling
  30. Front
    Cytochrome c
    Back
    Mobile protein carrier that transfers electrons from Complex III to Complex IV
  31. Front
    Complex I name
    Back
    NADH-CoQ oxidoreductase or NADH dehydrogenase
  32. Front
    Complex I electron source
    Back
    NADH
  33. Front
    Cofactors in Complex I
    Back
    FMN and Fe-S centers
  34. Front
    Electron acceptor from Complex I
    Back
    CoQ
  35. Front
    Function of Complex I
    Back
    Accepts electrons from NADH, transfers them to CoQ, and pumps protons
  36. Front
    Complex I reaction idea
    Back
    NADH + CoQ(ox) → NAD+ + CoQ(red)
  37. Front
    Complex I inhibitors
    Back
    Rotenone and amobarbital (amytal)
  38. Front
    Complex II name
    Back
    Succinate dehydrogenase
  39. Front
    Complex II special significance
    Back
    Also an enzyme of the TCA cycle
  40. Front
    Electron source for Complex II
    Back
    FADH2
  41. Front
    Electron acceptor from Complex II
    Back
    CoQ
  42. Front
    Proton pumping by Complex II
    Back
    Complex II does not pump protons
  43. Front
    Why FADH2 gives less ATP than NADH
    Back
    FADH2 enters at Complex II and bypasses proton pumping at Complex I
  44. Front
    Complex III name
    Back
    CoQ-cytochrome c reductase
  45. Front
    Electron donor to Complex III
    Back
    CoQH2
  46. Front
    Electron acceptor from Complex III
    Back
    Cytochrome c
  47. Front
    Components of Complex III
    Back
    Cytochrome b, cytochrome c1, and Fe-S protein
  48. Front
    Function of Complex III
    Back
    Transfers electrons from CoQH2 to cytochrome c and pumps protons
  49. Front
    Important carrier conversion at Complex III
    Back
    Converts a 2-electron carrier (CoQH2) into reduction of two 1-electron cytochrome c molecules
  50. Front
    Complex III inhibitor
    Back
    Antimycin A
  51. Front
    Complex IV name
    Back
    Cytochrome c oxidase
  52. Front
    Electron donor to Complex IV
    Back
    Cytochrome c
  53. Front
    Components of Complex IV
    Back
    Cytochromes a and a3 and CuA/CuB
  54. Front
    Function of Complex IV
    Back
    Transfers electrons to O2 to form H2O and pumps protons
  55. Front
    Most important fact about Complex IV
    Back
    Oxygen is the final electron acceptor
  56. Front
    Irreversible step of the respiratory chain
    Back
    Complex IV reaction
  57. Front
    Electrons required for complete reduction of O2
    Back
    4 electrons
  58. Front
    Why Complex IV architecture is important
    Back
    It helps prevent formation of partially reduced toxic oxygen species
  59. Front
    Complex IV inhibitors
    Back
    CN−, CO, NaN3, and H2S
  60. Front
    What electron transport does not do directly
    Back
    It does not directly put phosphate onto ADP
  61. Front
    Components of the electrochemical gradient in chemiosmotic theory
    Back
    A pH gradient and an electrical gradient
  62. Front
    pH gradient in oxidative phosphorylation
    Back
    Intermembrane space is more acidic and matrix is more alkaline
  63. Front
    Electrical gradient in oxidative phosphorylation
    Back
    Matrix is more negative than the intermembrane space
  64. Front
    Approximate ΔpH in the lecture
    Back
    About 1
  65. Front
    Approximate ΔΨ in the lecture
    Back
    About 0.15 V
  66. Front
    Matrix side of the proton gradient
    Back
    Alkaline and negative
  67. Front
    What drives proton flow back into the matrix
    Back
    The electrochemical gradient
  68. Front
    ATP synthase alternate name
    Back
    F1Fo-ATPase
  69. Front
    F1 portion of ATP synthase
    Back
    Projects into the matrix and contains the catalytic site for ATP synthesis
  70. Front
    F1 subunits listed in the lecture
    Back
    3α, 3β, γ, δ, ε
  71. Front
    Fo portion of ATP synthase
    Back
    Membrane part that forms the proton channel and rotates as protons pass through it
  72. Front
    First step in ATP synthase mechanism
    Back
    Protons move through Fo
  73. Front
    Effect of proton movement through Fo
    Back
    Causes rotation of the γ subunit
  74. Front
    Effect of γ subunit rotation
    Back
    Changes conformations of β catalytic subunits in F1
  75. Front
    Conformations of β subunits in ATP synthase
    Back
    O = open, L = loose, T = tight
  76. Front
    Rate-limiting step of ATP synthesis by ATP synthase
    Back
    Release of newly made ATP
  77. Front
    Protons through Fo required to synthesize 1 ATP
    Back
    3 H+
  78. Front
    Additional proton cost per ATP from phosphate transport
    Back
    1 H+
  79. Front
    Effective proton cost per ATP
    Back
    4 H+ per ATP
  80. Front
    Protons pumped when 2 electrons from NADH go to O2
    Back
    10 H+
  81. Front
    ATP yield when 2 electrons from NADH go to O2
    Back
    About 2.5 ATP
  82. Front
    Protons pumped when 2 electrons from FADH2 go to O2
    Back
    6 H+
  83. Front
    ATP yield when 2 electrons from FADH2 go to O2
    Back
    About 1.5 ATP
  84. Front
    P/O ratio for NADH
    Back
    2.5
  85. Front
    P/O ratio for FADH2
    Back
    1.5
  86. Front
    P/O ratio for cytochrome c to O2
    Back
    0.5
  87. Front
    Reason the P/O ratio is lower for FADH2
    Back
    FADH2 enters at Complex II and bypasses Complex I, so fewer protons are pumped
  88. Front
    Coupling in oxidative phosphorylation
    Back
    Electron transport, oxygen consumption, proton gradient, and ATP synthesis are tightly coupled
  89. Front
    Effect of rising ADP on oxidative phosphorylation
    Back
    ATP synthase works faster, protons flow back faster, and electron transport speeds up to rebuild the gradient
  90. Front
    Respiratory control
    Back
    If ATP synthesis is blocked, the proton gradient cannot be dissipated and electron transport slows or stops
  91. Front
    Main effects to know for inhibitors and uncouplers
    Back
    Effects on ATP synthesis, oxygen consumption, and catabolic rate
  92. Front
    Site of action of rotenone and amobarbital
    Back
    Complex I
  93. Front
    Specific block by rotenone and amobarbital in the lecture
    Back
    Between FMN and Fe-S in Complex I
  94. Front
    Effect of Complex I inhibitors on ATP synthesis
    Back
    ATP synthesis decreases
  95. Front
    Effect of Complex I inhibitors on oxygen consumption
    Back
    Oxygen consumption decreases
  96. Front
    Effect of Complex I inhibitors on catabolic rate
    Back
    Catabolic rate decreases because NADH cannot be reoxidized efficiently and upstream oxidative pathways slow
  97. Front
    Redox pattern around an ETC block
    Back
    Carriers before the block become reduced and carriers after the block become oxidized
  98. Front
    Site of action of antimycin A
    Back
    Complex III
  99. Front
    Effect of antimycin A on ATP synthesis
    Back
    ATP synthesis decreases
  100. Front
    Effect of antimycin A on oxygen consumption
    Back
    Oxygen consumption decreases
  101. Front
    Effect of antimycin A on catabolic processes
    Back
    Catabolic processes decrease because NADH and FADH2 oxidation backs up upstream
  102. Front
    Site of action of cyanide, carbon monoxide, sodium azide, and hydrogen sulfide
    Back
    Complex IV
  103. Front
    Why Complex IV inhibitors are especially dramatic
    Back
    They block the final transfer of electrons to oxygen
  104. Front
    Effect of Complex IV inhibitors on ATP synthesis
    Back
    ATP synthesis stops
  105. Front
    Effect of Complex IV inhibitors on oxygen consumption
    Back
    Oxygen consumption stops or falls essentially to zero
  106. Front
    Effect of Complex IV inhibitors on catabolic rate
    Back
    Catabolic rate decreases because NADH and FADH2 cannot be oxidized, so TCA and other oxidative pathways slow sharply
  107. Front
    Key concept in cyanide poisoning
    Back
    Oxygen may be present, but the cell cannot use it because Complex IV is blocked
  108. Front
    Oligomycin target
    Back
    Fo portion of ATP synthase
  109. Front
    Action of oligomycin
    Back
    Closes the proton channel and blocks proton reentry into the matrix
  110. Front
    Effect of oligomycin on ATP synthesis
    Back
    ATP synthesis stops
  111. Front
    Effect of oligomycin on the proton gradient
    Back
    Proton gradient becomes very steep because H+ cannot return through ATP synthase
  112. Front
    Effect of oligomycin on electron transport
    Back
    Electron transport stops because pumping more H+ becomes too difficult
  113. Front
    Effect of oligomycin on oxygen consumption
    Back
    Oxygen consumption decreases or stops
  114. Front
    Effect of oligomycin on catabolic rate
    Back
    Catabolic rate decreases because NADH oxidation slows
  115. Front
    Classic contrast with oligomycin
    Back
    Contrasted with uncouplers
  116. Front
    Examples of uncouplers
    Back
    DNP and thermogenin
  117. Front
    DNP
    Back
    2,4-dinitrophenol, a synthetic uncoupler
  118. Front
    Thermogenin
    Back
    UCP1, a physiologic uncoupler in brown adipose tissue
  119. Front
    Mechanism of uncouplers
    Back
    Carry H+ back into the matrix without ATP synthase and dissipate the proton gradient
  120. Front
    Effect of uncouplers on ATP synthesis
    Back
    ATP synthesis decreases
  121. Front
    Effect of uncouplers on oxygen consumption
    Back
    Oxygen consumption increases
  122. Front
    Effect of uncouplers on catabolic rate
    Back
    Catabolic rate increases because the cell burns more fuel trying to make ATP
  123. Front
    Effect of uncouplers on energy output
    Back
    Energy is released as heat
  124. Front
    Effects of ETC inhibitors such as rotenone, antimycin, and cyanide
    Back
    ATP synthesis ↓, oxygen consumption ↓, catabolic rate ↓
  125. Front
    Effects of ATP synthase inhibitor oligomycin
    Back
    ATP synthesis ↓, oxygen consumption ↓, catabolic rate ↓
  126. Front
    Effects of uncouplers such as DNP and thermogenin
    Back
    ATP synthesis ↓, oxygen consumption ↑, catabolic rate ↑, heat production ↑
  127. Front
    Proton-pumping complexes
    Back
    I, III, and IV
  128. Front
    Complex that does not pump protons
    Back
    II
  129. Front
    Mobile carriers in the respiratory chain
    Back
    CoQ and cytochrome c
  130. Front
    Final electron acceptor
    Back
    Oxygen
  131. Front
    Only irreversible reaction of the chain
    Back
    Complex IV reaction
  132. Front
    Why NADH gives more ATP than FADH2
    Back
    NADH enters at Complex I, whereas FADH2 enters at Complex II and skips one proton-pumping site
  133. Front
    Oligomycin vs uncouplers
    Back
    Oligomycin blocks H+ return through ATP synthase so ETC slows or stops, whereas uncouplers allow H+ return without ATP synthase so ETC speeds up

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