Introduction to the ETC
 The electron carrying
molecules, NADH and
FADH2, transfer their
electrons to a series of
compounds (mostly
proteins), which are
associated with the
cristae.
How it Works
 The protein/compounds
are arranged in order of
increasing
electronegativity…
therefore each successive
compound wants the
electrons more than the
one before it.
How it Works
 The compounds: NADH dehydrogenase, ubiquinone
(Q), the cytochrome b-c1 complex, cytochrome c,
cytochrome oxidase complex.
How it Works
 Each compound is reduced by gaining two electrons
from the one before it and oxidized by donating its
two electrons to the one after it.
How it Works
 As the electrons are passed they become more stable
and therefore generate free energy.
How it Works
 This free energy is used to pump protons into the intermembrane space
from the matrix (Active transport). There are three proton pumps.
 Oxygen is the final electron acceptor and it joins with two protons in
the matrix to form water.
Steps for NADH
 NADH gives up its two electrons to NADH
dehydrogenase.
Steps for NADH
 The mobile carriers Q and cytochrome c shuttle
electrons from one protein complex to the next until
they reach the final protein complex, cytochrome
oxidase.
 Along the way, as the electrons lose energy and become
more stable, 3 protons are actively transported from the
matrix into the intermembrane space.
Steps for NADH
 Here part of the cytochrome catalyzes the reaction
between the electrons, protons and oxygen to form
water.
Steps for NADH
 This process is highly exergonic (giving up free energy 222kJ/mol)…
the chemical potential energy of electron position is converted to
electrochemical potential energy of a proton gradient that forms
across the inner mitochondrial membrane.
 This energy will be used to power ATP synthesis in chemiosmosis.
Electrochemical Gradient
Intermembrane
space
Cristae
Matrix
Path of FADH2
 FADH2 skips the first
protein compound. This
means that FADH2
oxidation pumps two
protons into the
intermembrane space.
 Three ATP are formed
from the electrons from
NADH while only two ATP
are formed from the
electrons from ATP FADH2
as they begin with lower
energy.
NADH from Glycolysis
 Important to note that the
NADH formed in glycolysis
in the cytoplasm passes
into the mitochondrial
matrix through the
glycerol-phosphate shuttle,
where its electrons are
passed to FADH2, therefore
FADH2 essentially is
created in glycolysis,
therefore two ATP are
formed from that electron
carrying molecule.
NADH from Glycolysis
 There is another way that
NADH can pass its
electrons to another
NAD+ instead of FAD… it
is the aspartate shuttle,
but we will just assume
this one does not exist.
 There are many copies of
the ETC along the cristae;
therefore lots of ATP can
be produced.
Chemiosmosis and Oxidative
Phosphorylation
 There is an electrochemical gradient across the cristae.
(More protons outside than in the matrix)
 Two parts: difference in charge and a difference in
concentration.
Electrochemical Gradient
Intermembrane
space
Cristae
Matrix
Chemiosmosis and Oxidative
Phosphorylation
 The inner membrane is impermeable to protons.
 The protons are forced through special proton channels
that are coupled with ATP synthase (ATPase).
Chemiosmosis and Oxidative
Phosphorylation
 The electrochemical gradient produces a proton-motive
force (PMF) that moves the protons through this ATPase
complex.
Chemiosmosis and Oxidative
Phosphorylation
 Each time a proton comes through the ATPase complex, the free
energy of the electrochemical gradient is reduced and this
energy is used to create ATP from ADP + P in the matrix.
Chemiosmosis and Oxidative
Phosphorylation
 Peter Mitchell found all
this out in 1961 and
coined the term
chemiosmosis because
the energy that drives
ATP production comes
from the osmosis of
protons. It took a long
time for his theory to be
accepted. He finally got
his Nobel Prize in 1978.
It is about
time!
Chemiosmosis and Oxidative
Phosphorylation
 The continual production of ATP is dependent on the
maintenance of a proton reservoir in the intermembrane space.
This depends on the continued movement of electrons and that
depends on the availability of oxygen.
 Therefore we need oxygen to prevent the ETC from being clogged
up and we need food to provide the glucose that provides
electrons for the ETC.
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