In this figure you can see some negative
feedback loops. So the whole thing, you'll
recall negative feedback works by the end
product feeding back somewhere higher in the chain.
Cellular metabolism or cellular respiration is a
great example of how this happens.
For example, lets start just with ATP. If we
have tons of ATP, we really don't need to break down
more sugar and produce anymore ATP. So, ATP levels
are high, they are going to bind on to phosphofructokinase,
one of the enzyme in the process of glycolysis.
And they will shut down the action of phosphofructokinase.
I believe it's an allosteric inhibitor.
And that will shut the process down,
whereas if we have lots of ADP, we may see that
ADP allosterically activates phosphofructokinase
to allow it to take glucose and produce
more pyruvate and thus more ATP.
So, those two end products feedback in a negative
feedback loop in order to regulate the production
of themselves. Another couple of key pieces that act
in the regulation of these cycles would be NADH.
NADH, the electron electron carriers, when
there is tons of electron carriers,
and they all have their electrons and protons, and
they are off to the party at the electron transport chain,
then they will feedback on pyruvate oxidation
and prevent the production of more NADH's,
cause we don't need them. Finally, we'll look at citrate.
Citrate is one of the early intermediaries of the Krebs cycle.
Citrate can also feedback if there are high
levels citrate and act to negatively impact
the production of more citrate.
So, it's regulating the production of itself.
Again, negative feedback is one of the primary mechanisms
for controlling the rate of cellular respiration.
Regardless of which fuels we're using, we're going
to see that end products feedback to the beginning
to slow down the process. And if there's not enough
of the end products, then that will activate the process.
Bringing back together our conversation on enzymes, where
we considered allosteric activation and allosteric inhibition,
ADP and ATP play a primary role in regulating
the enzyme phosphofructokinase.
So now, you have a fairly good understanding of where all
three fuel types enter into the process of cell respiration.
We've learned that proteins and fats are broken down into
their constituents, and they enter cell respiration
at various points throughout the process. We also have
found that Acetyl CoA is a pivotal molecule in metabolism.
And we have learned that the products of cell respiration
also can feedback in a negative feedback loop
to regulate the whole process. So now, you should
be able to identify some of the entry points
for proteins and fats in the process of cellular
respiration, as well as describe some of the intermediates.
And finally you should be able to identify some of the
key regulators in the process of cell respiration.
Thanks so much for your attention. I look
forward to seing you in the next lecture.