Greetings. My name is Jerry Feigenson.
I am a professor at Cornell University in the USA.
Welcome to Part 2 of lecture 18.
We ended Part 1 with a brief discussion of
Peter Mitchell's breakthrough chemiosmotic theory
that energy is stored as a gradient of
protons and voltage across the inner mitochondrial membrane.
In this Part 2,
you will see four different protein complexes that make up
the mitochondrial electron transport chain. And finally,
we will look at the ATP synthase enzyme,
which uses this gradient to catalyze ATP synthesis.
We're going to look at reactions that happen in
liver mitochondria and especially with the inner membrane of the mitochondria.
So let me orient you.
The outer membrane of mitochondria is very permeable.
We'll show this as dashed lines schematically
indicating lots of holes in the outer mitochondrial membrane.
Then there's an inner mitochondrial membrane which is
extremely tight, extremely impermeable.
It's the tightest of all known biological membranes.
Then we'll notice that the cytosol has
a higher proton concentration and a more positive electrical potential than the matrix.
What about the enzymes that are involved?
Well, early on it was realized that there are
four protein complexes that are involved in ATP synthesis.
They are indicated as complex 1,
complex 2, complex 3,
and complex 4, and we're going to look at reactions in each one of these.
Now it's realized that complexes 1, 3,
and 4 seem to be loosely bound together into what could be called a super complex.
Actually, each complex by itself
can work to generate the proton and voltage gradient.
But now, complexes 1, 3,
and 4 are known to be associated and there's
further research going on to understand the importance of that finding.
It's these four complexes that get and give
electrons by means of mobile electron carriers.
So let's see how that works.