2. The Electron Transport Chain

Electron Transport Chain I

Stars everywhere, so many stars….. the following few lectures are complicated. I think what might help is an alternate explanation in cartoon style from the great Armando Hasudungan.


Complex IComplex_I.svg

  • electron donor: NADH, H+
  • electron acceptor: NADH-Q reductase
  • transported electron: 2
  • transported protons: 4
  • 42 subunits

Complex II



  • electron donor: FADH2
  • electron acceptor: Succinate dehydrogenase
  • transported electron: 2
  • transported protons: 0
  • Allows coupling of the CAC with Oxidative Phosphorylation
  • 4 subunits, 2 in matrix, 2 in IM.
  • FADH2 bound to sdha subunit
  • passes electron to a series of iron-sulfur centers in sdhb subunit
  • CoQ in shdc reduced to QH2 in subhd subunit
  • Path of electron determined by RP of carriers in the complex


Complex III

  • electron donor: Ubiquinol
  • electron acceptor: Cytochrome c reductase
  • transported electron: 1
  • transported protons: 4
  • Transfer of electrons from QH2 to cytochrome c, which is attached to the surface of the IM on the IMS.
  • Q cycle occurs here (see below)


Complex IV

  • electron donor: Cytochrome c
  • electron acceptor: Cytochrome c oxidase
  • transported electron: 1
  • transported protons: 2
  • Transfers electron from reduced cytochrome c to the final acceptor, I2 for form H2O.
  • 13 subunits, a dimer
  • Actually produces 2 H2O molecules, details murky


The two electrons and two protons given by NADH + proton lead to the formation of one molecule of H2O and transport 10 protons across the IM, which contribute to the proton gradient.




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