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In 1998
Roderick MacKinnon for the first time determined at
high resolution the structure of an ion channel. As
so often in biochemistry, form and function are
intimately connected. By showing what the protein
looked like at the atomic level, he also realised how
it functions.
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Ion
channels play an important role in how nerves
function. When for example a signal propagates
itself from the brain to the muscles it is all
about an interplay of chemical signals and ion
currents in the nerve cells. The picture
represents a nerve cell.
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How can
the channel let potassium ions pass but not, for
example, sodium ions? The oxygen atoms in the ion
filter form an environment which precisely mimics
that of the potassium ion outside the filter where it
is surrounded by water molecules. So the potassium
ion can slip out of its "water coat" and pass through
the filter without noticeable resistance.
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The
sodium ion, which is smaller than the potassium
ion, draws water molecules more closely to
itself and is too small to fit snugly between
the oxygen atoms in the ion filter. Sodium ions
therefore remain in the water outside the
channel.
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