Cells use a proton-pumping system made up of proteins inside
the mitochondria to generate ATP. Synthesis of ATP is coupled
with the oxidation of NADH and the
reduction of O2 in Electron
Transport (both future topics). There are three key steps
in this process:
1.Electrons are transferred from NADH, through a series of
electron carriers, to O2.
2.Transfer of electrons by these carriers generates a proton
(H+) gradient across the inner mitochondrial membrane.
3.When H+ spontaneously diffuses back across the inner
mitochondrial membrane, ATP is synthesized.
ATP synthetase converts the free energy of the proton gradient
to chemical energy in the form of ATP. It consists of two main
ATP synthetase (multicolors) has two components: a proton
channel (magenta) which allows diffusion of protons down a concentration
gradient, from the intermembrane space, and a catalytic component
(F1) to catalyze the formation of ATP in six alpha beta subunits
(multicolors) in graphic on the left.
Every time three protons are pumped through the channel, the
F1 subunit rotates 120 degrees. The actual synthesis (formation
of the bond between ADP and Pi is catalyzed by conformational
changes of the enzyme that occur as a consequence of the rotation.
The key point is that the rotation moves the beta subunit
that contains ADP + Pi to a new position. In this new position
the beta subunit would rather bind ATP, and thus catalyzes the
formation of a ATP from the bound ADP and Pi. The newly-formed
ATP is released with the transport of an additional proton. Three
protons must be transported to make one ATP. Look at one or more
of the animations below for a more complete description.
ATP Synthetase - Chime
in new window
of ATP synthesis - Thomas M. Terry, The University of Connecticut
animation of ATP synthesis - Carnegie Mellon University
Move - Great but 6MB size - Thomas M. Terry, The University