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Ch.19 Oxidative Phosphorylation - Coggle Diagram

- - - - • One-electron carriers
      - • Iron coordinating porphoryin ring derivatives
      - • a, b, or c differ by ring additions
    - - • One-electron carriers
      - • Coordinating by cysteines in the protein
      - • Containing equal number of iron and sulfur atoms
    - - • Ubiquinone is a lipid-soluble conjugated dicarbonyl compound that readily accepts electrons.
      - • Upon accepting two electrons, it picks up two protons to give an alcohol, ubiquinol.
      - • Ubiquinol can freely diffuse in the membrane, carrying electrons with protons from one side of the membrane to another side.
      - • Coenzyme Q is a mobile electron carrier transporting electrons from Complexes I and Il to Complex Ill.
  - - - • One of the largest macro-molecular assemblies in the mammalian cell
      - • Over 40 different polypeptide chains, encoded by both nuclear and mitochondrial genes
      - • NADH binding site in the matrix side
      - • Noncovalently bound flavin mononucleotide (FMN) accepts two electrons from NADH.
      - • Several iron-sulfur centers pass one electron at a time toward the ubiquinone binding site.
      - NADH:Ubiquinone Oxidoreducase Is a Proton Pump
        
        • Transfer of two electrons from NADH to ubiquinone is accompanied by a transfer of protons from the matrix (N) to the intermembrane space (P) .
        
        • Experiments suggest that about four protons are transported per one NADH.
        
        • Reduced coenzyme Q picks up two protons.
        
        • Protons are transported by proton wires.
    - - • Electrons are passed, one at a time, via iron-sulfur centers to ubiquinone, which becomes reduced QH2
      - • Does not transport protons
      - • Succinate dehydrogenase is a single enzyme with dual roles:
        
        convert succinate to fumarate in the citric acid cycle
        
        capture and donate electrons in the electron transport chain
      - • FAD accepts two electrons from succinate
    - - • Uses two electrons from QH2 to reduce two molecules of cytochrome c
      - • Additionally contains iron-sulfur clusters, cytochrome b, and cytochrome c
      - • Clearance of electrons from the reduced quinones via the Q-cycle results in translocation of four additional protons to the intermembrane space.
      - The Q cycle
        
        • Experimentally, four protons are transported across the membrane per two electrons that reach cyt c.
        
        • Two of the four protons come from QH2.
        
        • The Q cycle provides a good model that explains how two additional protons are picked up from the matrix.
        
        • Two molecules of QH2 become oxidized, releasing protons into the IMS.
        
        • One molecule becomes rereduced, thus a net transfer of four protons per reduced coenzyme Q.
        
        cycle
        
        cycle 1
        
        cycle 2
        
        Overall Reaction
        
        :star: Cytochrome c
        
        The second mobile electron carrier
        
        Ubiquinone moves through the membrane.
        
        Cytochrome c moves through the intermembrane space.
        
        A soluble heme-containing protein in the intermembrane space
        
        Cytochrome c carries a single electron from the cytochrome bC1 complex to cytochrome oxidase.
    - - • Mammalian cytochrome oxidase is a membrane protein with 13 subunits.
      - • Contains two heme groups: a and a3
      - • Contains copper ions
      - :star: Electron Flow Through Complex 4
- - - - soluble complex in the matrix
      - individually catalyzes the hydrolysis of ATP
    - - integral membrane complex
      - transports protons from IMS to matrix, dissipating the proton gradient
      - energy transferred to Fl to catalyze phosphorylation of ADP
  - - - NAD* pools are kept segregated and cannot directly cross the mitochondrial inner membrane.
      - Two methods are used to feed the electrons from NADH from the cytosol into the mitochondria:
        
        malate-aspartate shuttle
        
        glycerol-3-phosphate shuttle