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So
how do hydrogen electrons get trapped?
The last step in the reactions that
moves energy into ATP is called electron transport. Electron
transport is achieved by passing the electrons of hydrogen through four complexes
of proteins.
Where
do the electrons come from?
The electrons of
hydrogen (from the Krebs Cycle, remember?) are pulled off and
transported by a series of proteins that are anchored in the
inner membranes of mitochondria. Electrons
are attracted to these proteins by the highly positive-charged
iron atoms that are in the proteins.
Think of it as if each complex were
a basketball player, passing the ball (electron) to the next
player, and so on. Because the electron has electric charge,
there is associated force or energy. There is a gradient in
electric charge as the electron moves from one hydrogen atom
to another. The energy of these gradients gets captured
in ATP.
 Another
way that energy changes have been described is in terms of a waterfall
that has several steps. At the top, the water (electrons) has
the most energy, with less energy at each step toward the bottom.
If a paddlewheel is placed at each step, the energy of the falling water could be stored in a battery for example
(in cells, ATP is like a battery).
Oxygen is consumed ("burned")
in the process, because it reacts with hydrogen to form water. So, you can see
that there is such a thing as metabolic water. Animals
that live in the desert, such as camels, are especially good
at taking advantage of metabolic water to stay alive.
To learn more about why our bodies need oxygen (click
here.)
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