Transcript Document

Chemiosmotic mechanism of
oxidative phosphorylation
Active transport carrier proteins set
up gradients which are then used to
synthesize ATP
ATP synthase
• Mitochondria are present in nearly all
eucaryotic cells, plants, animals, and most
eucaryotic microorganisms.
• Mitochondria metabolize acetyl groups via
the citric acid cycle, producing CO2 and
NADH - an activated carrier molecule that
carries high-energy electrons.
• NADH donates its high-energy electrons to
the electron-transport chain in the
mitochondrial membrane, oxidizing NADH
to NAD+.
• The electrons are quickly passed along the
chain to molecular oxygen to form water.
• Energy released during the passage of
electrons is used to pump protons and create
a proton electrochemical gradient.
• The proton gradiant drives the synthesis
of ATP by oxidative phosphorylation - the
addition of a phosphate groups to ADP
using this process requires oxygen.
• These events also take place in aerobic
bacteria, using the plasma membrane.
Mitochondrion contains
two membrane-bound
compartments. They are
similar in size to bacteria,
contain their own DNA
and RNA and a complete
transcription and
translation system
including ribosomes
(different from the cellular
ribosomes). They
constantly change shape
and position. Form long
moving chanis in
association with
microtubules of the
cytoskeleton
The linking of
electron
transport, proton
pumping, and
ATP synthesis is
called
chemiosmotic
coupling.
The mitochondrial electron-transport chain are grouped into three large
respiratory enzyme complexes, each containing multiple individual
proteins.
Each complex
contains metal
ions that form a
pathway for the
passage of
electrons
through the
complexes.
This powers the
pumping of
protons into the Intermembrane space
Since protons are positively charged, they will move across the
membrane, since it has a excess of negative electrical charges on the
other side. Therefore, the proton gradient created across the inner
mitochondrial membrane is very steep, consisting of the electroattractive
force and the concentration gradient set up by pumping protons into the
intermembrane space - electrochemical gradient. This gradient is used
to drive ATP synthesis by oxidative phosphorylation.
ATP synthase
ATP synthase is a reversible coupling device that can convert the
energy of the electrochemical proton gradient into chemical bond
energy or vice versa. The direction depends on the magnitude of the
electrochemical proton gradient.
In many bacteria
that can grow
either aerobically
or anaerobically,
the direction in
which the ATP
synthase works is
routinely
reversed when
the bacterium
runs out of
oxygen.