So breaking that down a little bit more, let's look
at how this electrochemical gradient is created.
We have a number of different electron acceptors
embedded together in the inner mitochondrial membrane.
So you'll recall the mitochondria has two membranes.
An external membrane and then a convoluted
internal membrane. And we are going to be
pumping hydrogens into that tight space.
So it's much easier to create a gradient in that way.
So, what will happen first is the electrons will be
picked up by the first electron acceptor. Now, this is
where I introduced the idea between NAD taxis
and FAD budget taxis. The NAD taxis will receive
electrons at a higher level in the staircase.
I imagine these electron acceptors as a staircase and
the electrons are simply bumping down the staircase
each time releasing a little bit of energy. The energy
that they release is used to pump hydrogen ions
across into the intermembrane space. So, FAD drop off
their electrons at a slightly lower level.
And then that acceptor molecule will pass them on to
the next molecule, and the next molecule,
and so on and so forth bumping them down the chain
until oxygen is the final electron acceptor.
Now we say its a 1/2 O2 because in the end we're going
to generate water, and water has H2 and 1O,
but also, it's one of the few places that we see
oxygen not in the form of O2. Oxygen is separated
and becomes very electronegative. Cause you'll recall
it really wants to bond with another oxygen.
So it becomes very electronegative and in this sense,
that electronegativity, that very strong draw for
electrons is what pulls the electrons down this
energy staircase. The 1/2 O2 is on the inside
in the mitochondrial matrix. It's going to grab those
electrons and hold on to them for a moment.
Let's look at where the H's come from. The H's are
being pumped across into the intermembrane space,
and now we have a strong desire for them to come back in.
Well, let me continue a moment with my analogy of
the prom or the dance we've gone to. Things get a
little bit complicated. The taxis have dropped off
all of the girls and the boys at this point at the top
of the electron transport chain. It's a staircase.
There is a staircase that goes down into the dance.
And the door guy, the guy that's running the door,
the first electron acceptor says "Hey ladies, welcome.
Come on down the stairs", and he lets all the ladies
walk down the stairs. So the electrons happily make their
way down into the dance and are having a great time
chatting with each other. Meanwhile, this bouncer, the
door guy is not such a nice guy to the protons,
the hydrogens. So he throws them out the back door
into the alley or the intermembrane space.
He throws them out into the alley. Now they're back
there and they are angry. And there is lots of them
back there. They are so upset and they are going looking
for a doorway to come back in and meet up with the girls.
So, that's the situation.
So now that we have created this big gradient, we have
to get the hydrogens back into the dance next to their
electrons to have a great time. But in this
process, we are going to make tons of energy.
So this is where all the pieces come together to form
lots and lots and lots of ATP. Huge yields.