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  • The following complexes are found in the electron transport chain:

  • and the complex that makes ATP,

  • In addition to these complexes, two mobile carriers are also involved:

  • Other key components in this process are

  • and the electrons from it,

  • which combine to form ATP.

  • At the start of the electron transport chain,

  • two electrons are passed from NADH

  • into the NADH dehydrogenase complex.

  • Coupled with this transfer is the pumping of one hydrogen ion for each electron

  • Next, the two electrons are

  • transfered to ubiquinone.

  • Ubiquinone is called a mobile transfer molecule

  • because it moves the electrons

  • to the cytochrome b-c1 complex.

  • Each electron is then passed from the cytchrome b-c1 complex to cytochrome c.

  • Cytochrome c accepts each electron one at a time.

  • One hydrogen ion is pumped through the complex as each electron is transfered.

  • The next major step occurs in the cytochrome oxidase complex.

  • This step requires four electrons.

  • These four electrons interact

  • with a molecular oxygen molecule and eight hydrogen ions.

  • The four electrons, four of the hydrogen ions, and the molecular oxygen,

  • are used to form two water molecules.

  • The other four hydrogen ions are pumped across the membrane.

  • This series of hydrogen pumping steps creates a gradient.

  • The potential energy in this gradient

  • is used by ATP synthase to make ATP

  • from ADP and inorganic phosphate.

  • The ATP synthesis steps you see here

  • are discussed in greater detail in the ATP sythase gradients animation.

  • This animation illustrates two full cycles of electron donation.

  • In biological systems, however,

  • many electron transport cycles occur simultaneously

  • --helping to ensure that the proton gradient is always maintained.

The following complexes are found in the electron transport chain:

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