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This blog intends to display concepts, informations, musics, videos, games, cartoons, curiosities about biochemical issues. Because Biochemistry does not have to be incomprehensible...
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Cellular respiration - Chemiosmotic theory
The
chemiosmotic theory, postulated in 1961 by Peter Mitchel explains how the
transport of electrons along the mitochondrial respiratory chain is related to
the synthesis of ATP. In fact, as the electrons go through the respiratory
chain complexes, they behave like that are moving down an "energy
staircase", always passing gradually to a lower energy level. In other
words, there are small amounts of energy that are released, which individually
are not useful to the cell. However, part of this energy is used to pump
protons into the intermembrane space, that is, part of the energy is stored in
the form of an H+ gradient. This gradient allows the accumulation of a large
amount of energy, because this is an electrochemical gradient. It is a chemical
gradient, because we are talking about an asymmetry of H+ concentrations
between the two sides of the inner membrane. But it is also an electrical
gradient, as it is also created an asymmetry of charged between both sides of
the membrane, because the H+ is pumped into the intermembrane space without
sending any counterion. Thus, there is an accumulation of positive charges in
the intermembrane space, as compared while the matrix becomes more negative. By
now many must be wondering "But what is the use of this process? Why does
the cell needs a gradient of H+? "The chemiosmotic theory explains just
that!
In addition
to the mitochondrial respiratory chain complexes, there is also a membrane
enzyme (localized in the inner membrane), called mitochondrial ATP synthase
(more about this enzyme here). This enzyme has a catalytic subunit, responsible
for the synthesis of ATP, and a subunit that functions as a transmembrane pore
for the passage of protons. So, the idea is simple... the protons that
accumulate in the intermembrane space, will cross the inner membrane through
this pore, and since this transport occurs driven by the electrochemical
gradient, it releases energy. This energy is used by ATP synthase to produce
ATP.
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