Way back at the beginning of
A&P 1 (and at the beginning of your science education) you learned about chemicals and
how they build cells. Well, now it's time to use that information in another way!
Hormones are simply chemicals that cells make and then spit out into
the blood. There is a variety of types of chemicals made in our bodies, so there is
also a variety of types of chemicals that can be hormones. Some of the chemicals
that can be hormones include hydrophobic molecules-- remember that term? Hydrophobic
is water-hating... these molecules are mainly lipids and are full of nonpolar covalent
bonds. Anyway, an example of a hydrophobic hormone is a steroid hormone.
Steroids are a type of lipid. There are lots of hydrophilic molecules that are
hormones as well. Some of the hydrophilic molecules that can serve as hormones will
be more familiar to you (like proteins) than others.
The big distinction between types of chemicals that can be hormones
(in trying to understand how they act on cells and tissues) is whether the hormone is a
hydrophilic or a hydrophobic molecule. Consider the following: a hormone has
to travel in the blood (which is mainly water) AND a hormone has to bang into a cell
membrane (which is mainly lipid). Something that is hydrophilic will do these things
differently from something that is hydrophobic... that is the subject of the next web
page. But I hope you can see why it matters whether a hormone is one or the other
for right now.
Now, I'll describe (some of) the types of molecules that can act as
hormones in the human body. Keep in mind that there are tons of hormones, and even
more exist than we can describe here. But we will do a pretty thorough job on the
major human hormones.
Hydrophobic Hormone Molecules
Steroids
All steroids have basically the same structure-- they are molecules
modified from cholesterol. They all have the same four rings as cholesterol (3 are
hexagons, one is a pentagon). The only way they differ is in the side groups they
have sticking off the rings.
If you look at this picture of cortisol and aldosterone, you should
see that they differ in only two side groups (both off the hexagon). Can you see
that? Otherwise, they should look pretty similar.
Estrogen and testosterone are also steroids. Our bodies use
many steroids for a variety of purposes.
Hydrophilic Hormone Molecules
Amines (modified amino acids)
We have lots of amino acids readily available in our bodies, since
we use them to make proteins. Some of these can get modified by
adding certain groups onto them... this changes
them enough to no longer call them amino acids, but to now call them "amines."
One particular amino acid that is the starting point for
manufacturing many of our amines is tyrosine. Our cells change tyrosine through
chemical reactions into epinephrine and/or norepinephrine. Some cells can also
change them more and make dopamine or serotonin, but those are mainly neurons that can do
that.
If you take a look at the diagram of epinephrine and norepinephrine
to the right, you can see the amino acid basis within them-- the two carbons in NE that
are not in the ring are the original central carbon of the amino acid (the one on the
right) and carbon of the carboxyl group (the one on the left). The amino group is
off to the right. The carboxyl group was the part that was modified to make the
amine... a six carbon ring was added to it.
I will NOT ask you to draw any of these chemicals, but I have
explained them in the hope that you will understand them better.
Another set of amine hormones are the thyroid hormones. Take a
look at this picture of thyroid hormones to the left...
At the bottom of each you can see a "NH2CHCOOH."
This stands for a:
|
NH2-C-COOH
|
H
That is the main portion of an amino acid (the amino group to the left, the carboxyl
group to the right). Off the top would be the R group. In the case of thyroid
hormones, the R group has been modified to have these large rings with iodine atoms
attached. We'll discuss this more on the thyroid gland page.
Peptides
The word peptide means a short chain of amino
acids. Basically, a peptide is a polypeptide, but with fewer than about 15 amino
acids making it up. There are so few amino acids 
that the polypeptide cannot fold into any sort of complicated
three-dimensional shape like a protein can.
Because they are made of amino acids, peptides are hydrophilic.
They are also much smaller than full proteins, since a protein has typically
hundreds or thousands of amino acids. Some proteins have fewer, even only around 50
or so amino acids. But really short chains of amino acids are called peptides
instead of proteins.
Take a look at this picture of oxytocin (OT) and of antidiuretic
hormone (ADH). These two hormones are both peptide hormones; coincidentally, they
are both manufactured in the hypothalamus.
OT and ADH have only 9 amino acids that make them up. If you
aren't used to looking at a picture like this one, each circle with letters in it is an
amino acid. "Cys" stands for cysteine, "tyr" stands for
tyrosine, etc. The only difference between OT and ADH ist that there is a leucine in
OT (It should read Leu, but they seem to have a typ-o there) and a phenylalanine (Phe) in
ADH.
Proteins
You learned what proteins are back in chapter 2, at the very start
of last semester in our "review" section during unit 2. Proteins are made
up of long strings of amino acids... the polypeptide chain that is the result of putting
all these amino acids together then folds up into a tertiary, and sometimes quaternary,
shape. We will be studying a few protein hormones in this unit.
One such hormone is insulin; insulin is a protein hormone that is
somewhat small for a protein. Also, parathyroid hormone is a protein-- you already
heard about this hormone when we studied bone. Your book mentions that some hormones
are actually even glycoproteins instead of just plain proteins; the
glyco- part of that word stands for the fact that sugar groups are attached to those
proteins.
Other types of hormones
There are other types of chemicals that make up hormones. Your
book mentions prostaglandins. We won't get into the structures of any of these other
types.
