• NADH and FADH2 carry electrons to the ETC
  • Each become oxidized, losing two electrons to the ETC

The Electron Transport Chain (ETC) Structure

  • Located within the inner mitochondrial membrane
  • Composed of various protein structures arranged in order of increasing electronegativity
  • Ex. weakest electron attractor (NADH dehydrogenase) is at the beginning of the chain and the strongest   (cytochrome oxidase) at the end

How it Works:

  • Electrons pass from one component protein in the chain to the next
  • As they move from molecule to molecule they occupy ever more stable position relative to the nuclei of the atoms they associate with;
  • Free energy released in the process is used to move protons [H+ ions] from the mitochondrial matrix to the intermembrane space
  • Electrons reaching the end of the chain are in very stable positions and require the extremely electronegative oxygen to remove them from the ETC


  • NAD+ and FAD+ are in limited supply and must be oxidized by the ETC to reuse them
  • Electrons must be removed from the ETC by oxygen to keep the ETC working


  • Drops electrons off at first complex; moves 3 H+ ions; produces 3 ATP
  • GLYCOLYSIS: NADH cannot penetrate the mitochondrial inner membrane, however a membrane shuttle transfers electrons from the glycolysis NADH to FAD to produce FADH2


  • Drops electrons off at cytochrome Q; moves 2 H+ ions; produces 2 ATP

Chemiosmosis and Oxidative ATP Synthesis

  • The intermembrane space is impermeable to H+ ions
  • Pumping H+ ions out of the matrix and into them intermembrane space creates an electrochemical gradient
  • Electron free energy is transferred to potential energy in the electrochemical gradient

Electrochemical gradient:

  • Higher positive charge [H+ ions] in the intermembrane space than in the matrix
  • Higher concentration of H+ ions in the intermembrane space than in the matrix

Proton-Motive Force (PMF):

  • Created by the H+ ions desire to move away from each other because they repel one another (like charges) and the want to diffuse into the matrix (low H+ conc.)
  • Causes H+ ions to move around in the intermembrane space

ATP Generation:

  • Unable to move through the inner membrane, H+ ions are forced to move through special protein channels called ATP synthase
  • Free energy of the electrochemical gradient drives the synthesis of ATP from ADP and Pi in the matrix; chemiosmosis


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11 years ago

Thank you very much

Berenice Rivera Cruz
Berenice Rivera Cruz
11 years ago

To whom it may concern, My name is Berenice Rivera Cruz and I am currently a doctoral student in the program of Nurse Anesthesia at Virginia Commonwealth University. As part of my degree requirements I wrote an article in Mitochondrial Myopathies. I have been asked to submit it for publication in the American Association of Nurse Anesthetists Journal and wanted to obtain permission to include your Figure J-13:Electron Transport Chain in it with all due credit, of course. Please let me know what you would require to grant me this authorization. Have a wonderful Holiday Season! Very truly yours, Berenice… Read more »