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.