The point here is that electron transport chain
and chemiosmosis are the primary ATP production
area and they are utilizing all of the energy,
the potential energy that was captured by the
electron carriers bringing them to the electron
transport chain. So let's talk a little bit about
yields and where things come from. This figure is a
fantastic summary of where each of those molecules
come from. Our carbons, our electron carriers and
our ATP. You'll notice that there are couple of ATP
made directly through glycolysis. And there are couple
of ATP that are directly made from the Krebs cycle.
However, the majority of those ATP are going to be made
from electron carriers that are carrying electrons to the
electron transport chain.
So we have a little bit of a currency we consider when
calculating how many ATP get made from each glucose.
And I have to tell you ahead of time, it's a little bit
more complicated than it previously was thought.
We previously made sort of an exchange rate for ATP and
NADH and FADH. First of all, that we get 2.5 ATP on average
per NADH per 2 protons, 2 electrons. And we get 1.5
for the FADH2. You'll recall that came in at a
slightly lower level on the electron transport chain.
And that means that in all we should have a
certain number of ATP. Recall we got 2 from glycolysis,
and we got a couple from the Krebs cycle.
And when we consider all that we got from each of the
processes, we should end up with 28, 30 ATP.
You may have heard that there were 32 to 36 ATP made.
This is where it gets confusing.
When you do the accounting for what happens now that we
are learning more about the ATP synthase molecule,
some other ATP's may be lost. So let's just go with the
number of around 30, and recall that this is probably
the exchange rate that you'll be offered. And you
can make your calculations based on that,
but also be aware that probably there is a lot more
going on and it's not quite as simple as we think.
The accounting when it comes to ATP synthase doesn't
quite work out. But we are still in the discovery stages
of how that enzyme works. So let's look though at
efficiency, because you'll be surprised that
efficiency of glucose metabolism in the
presence of oxygen is pretty good.
Recall that glycolysis we make just a very little bit
of ATP. And then the majority of it is made
when we have oxygen present and can go through the
Krebs cycle and can go into the electron transport chain
and chemiosmosis. When we do that, we are
producing 686 kcal/mol of glucose.
And if you think about what ATP is worth. ATP
is worth 7.3 kcal/mol. So when we do our
math for this, we can divide the two and find out that
considering 30 ATP was made on the most conservative side
then we have a 32% efficiency which is more
efficient than most cars on the road.
Of course cars are getting much more efficient these
days but still it's a pretty efficient system.
When you consider that yeasts and such and some
bacteria are anaerobic, they don't have the Krebs cycle
or electron transport chain and chemiosmosis. They are
only producing 2 ATP per glucose or, yeah 2 per glucose.
And so it's not entirely an efficient system for them.
So you think about how much more powerful
it is to be able to use oxygen in
the metabolism of our fuels.
So, here is a summary figure of all
of the stages we've been through.
We had glycolysis which occurred outside of the
mitochondria in the cytosol of the cell.
We had to further oxidise the 2 pyruvates to get them
across the mitochondrial membranes and into the matrix
in the process of pyruvate oxidation. And then in the
Krebs cycle, that occurs all the way on the inside
of the cell. I mean in the site of the mitochondria. So
then that we can pump the hydrogen ions out through
the inner mitochondrial membrane into that
intermembrane space, in order for chemiosmosis and
oxidative phosphorylation to happen which is where we
get all of our ATP. Again, this is a great summary
image for the entire process of cellular respiration.
By now, you should be able to track your carbons. You
should be able to track your electron carriers
as well as ATP. And where each of those is
generated and where they go.
For example, where do all these electron
transporters go? You should be able to describe how
the electrochemical gradient is formed
during the electron transport chain.
As well as the functioning of ATP synthase. How does
that work in order to form so much ATP.
So I hope you have a great understanding of
cellular respiration at this point.
I look forward to moving on to look at how different
foods are metabolized, and how they fit into this
process of cellular respiration.
Thanks so much for listening.