Now ketone bodies are
very important molecules.
What they are, are little pieces of carbon and in
this we can see we start with a 6 piece of
6 carbon piece known as HMG-CoA.
And it's broken down into acetyl-CoA
which contains two carbons
and the acetoacetate. And the acetoacetate
is the first of the ketone body.
Why do we care about an acetoacetate?
The reason we care about it
is it can be broken down
into acetyl-CoA by cells.
Now ketone bodies are very important energy
sources for cells when they run out of glucose.
Ketone bodies are produced by the liver
down into the blood stream when glucose
is not available. So people who are taking
either of very very lower carb
diet, people who are starving
or people who have problems with glucose
metabolism may have very low blood glucose.
And when that happens having an
alternate energy source is important.
And the ketone bodies provide
that important resource.
Now acetoacetate, as we can
see in a second, is unstable.
Acetoacetate can spontaneously
decarboxylate to become acetone.
Now spontaneously decarboxylate
means it doesn't take an enzymes
so the molecule itself is
unstable and that can happen.
Acetone can be smelled in a person's breath.
And acetone smells like a finger nail polish remover.
And it's always important to remember that if
you ever smell acetone on someone breath
to have them check things out
with their doctor; because,
that typically means that they
are not doing something unusual
that they may some problems with glucose metabolism
that they are not aware of, most commonly
diabetes. And in fact a lot of
people discovered they have diabetes
when a friend tells them. They
can smell acetone on their breath.
So acetoacetate can be converted into
couple of things as described and that
involves acetone by the spontaneous
decarboxylation here. Or more importantly
into 3-hydroxybutyrate by
the enzyme shown in the screen.
This reaction is actually a
reduction in which electrons
from NADH are added to acetoacetate to create
the molecule on the right, 3-hdroxybutyrate.
We described 3-hydroxybutyrate as a ketone
body, but technically it's not a ketone.
But it does participate in
the ketone body process.
Acetone that is produced by
the spontaneous decarboxylation
can be exhaled into lungs or removed by the kidneys
from the blood stream and acetone really isn't a very
useful molecule for the body so that
if the acetoacetate goes to acetone
it's actually wasting some of the energy that
would be available otherwise to the cells.
Now the acetoacetate and 3-hydroxybutyrate
are water soluble and readily travel in the
blood very much like glucose travel in the blood
and they can get to target tissues.
When they get to target tissues,
the acetoacetate can be broken down
back into 2 acetyl-CoAs.
Well 2 acetyl-CoAs are very helpful
for cells; because, they provide energy for
brain and eyes and things like that, that need
that continual energy source.
So, thanks to ketone bodies.
The body is able to provide energy
to cells when glucose is low.