Now cholesterol, as I said, is a
precursor of the steroid hormones and steroid
hormones play very important roles in our body.
There are 5 classes of steroid hormones.
The first of which we called the
progestogens; because, cholesterol
is converted into progestogens. One of which is
progesterone as you see on the screen.
And the progestogens are the precursors
of the other steroid hormones.
Now notice I am saying progestogens and it
spells like it's progestogens and it's actually
spelled in both ways so the "O" and A"
in progestogens are equivalence balance.
In any way the progestogens can be
converted into the other classes
of steroid hormones and these are all
classes of hormones many related compounds.
One is the glucocorticoids that you can see here. The
other is the mineralocorticoids that you can see here
and the third is the androgens here.
Now the androgens themselves which are the male sex hormones
are the precursor of the female hormones known as the estrogens.
And in going from the androgens on
the right to the estrogens to the left
we see that the lower left
ring on the androgens
has a single double bond. But the lower left
ring on the estrogen is a benzene ring.
That involves creation of an aromatic ring and
that's a very unusual reaction in biology.
This is about the only place
where an aromatic ring is created by an enzyme.
And the enzyme that creates
this is known as an aromatase.
An aromatase catalyzes this conversion.
Now, I tell you that; because, this is an
important for enzyme for health purposes.
Many tumors are estrogen sensitive. Meaning
that when they bind to estrogens
are stimulated to grow.
These tumors are more of a factor in women although men
do have some estrogens within their bodies as well.
If your doctor senses a tumor or detects a
tumor in you, one of the first test will be
on that tumor is to see
if it is estrogen sensitive;
because, if the tumor is estrogen sensitive then the
doctor is going to use as part of their treatment
an aromatase inhibitor
to stop the production of estrogens.
And if that happens then many times the
tumor can be very effectively controlled.
In addition to being the precursors
of the steroid hormones, the
cholesterol is also a precursor of
important compounds called bile acids.
Now I have shown three bile acids on the screen and you can
see that of course their structures resemble that of cholesterol.
Bile acids play a very
important role in solubilizing
fat in your digestive system.
So they come from bile and bile is
there to help emulsify fat, fat
soluble vitamins and cholesterol.
So the first step in that process that
I showed you on the screen earlier
the movement of cholesterol in the
body, the very step happens before
the cholesterol, and the fats and the
fat soluble vitamins get transferred
across the intestinal wall. The first
step is they get emulsified in water.
Well emulsification is just a fancy way of saying "making
them dissolve" and that's what soaps do with grease
and that's what bile acid
do with these compounds.
In this lecture, I have gone through the synthesis
of cholesterol from very simple compounds like
acetyl-CoA and how cholesterol
can be converted into other compounds that are important in
our body such as the steroid hormones and the bile acids.
I hope in the presentation the message you
take away is that while cholesterol
is associated with some very
detrimental health problems,
cholesterol is necessary for
functioning in the animal body.