- [Instructor] Alright, in previous videos
I introduced steroids
to you as one example
of the chemical messages
that our body parts choose
to communicate with each
other, and we call those
chemical messages, hormones.
But I haven't really gotten
to tell you all about steroids
and where they come from
and how they're made
and that's what I wanna do today,
and so to accomplish that I really need
to start by introducing you to terpenes,
and terpene might not be
the most familiar of words,
but it refers to a
class of lipid molecules
that are made of a repeating, distinct set
of carbon atoms called isoprene.
And so I'll draw in that
carbon unit called isoprene.
And isoprene has this
really distinct structure
of four carbons chained together,
so one, two, three, four,
with the fifth carbon branching
off of one of the middle carbons.
And this five-carbon unit repeats to build
larger and larger molecules.
And so as two five-carbon
isoprenes come together,
you get a molecule that has 10 carbons,
and we call that a monoterpene.
And one of my favorite
monoterpenes right now is menthol,
which looks like this.
And this little guy is super helpful
to me right now because I've had
a pretty rough cough for the past week,
and my cough drops are
filled with menthol.
And then if you add one more isoprene,
you'd have 15 carbons,
and that would give you
three units of isoprene,
and we'd call it a sequiterpene.
And one example of a
sequiterpene is ginger,
and ginger looks like this.
But you can see that ginger is made up
of three isoprene units and it
fills up gingersnap cookies,
and those are my favorite
types of cookies.
Really you can just keep adding
these isoprene units and making
larger and larger molecules,
and so I'll just go ahead
and make a chart here.
And remember monoterpenes
had two isoprene units,
and sequiterpenes had
three isoprene units,
and if you added another
isoprene unit to that
you'd have a diterpene,
and it would have four isoprene units,
making 20 carbons, and it's called
a diterpene now because it's really
just two monoterpenes put together.
And then you could add another one,
and that would give us five,
and five isoprenes for 25 carbons,
and that would be a sesterterpene,
and you could just keep going,
and you could have six isoprene units,
for 30 total carbons,
and that would be a triterpene,
because essentially now we've got
three monoterpenes, and then if you
added another monoterpene to
that you'd have a tetraterpine,
and that would have 40 carbons,
and eight isoprene units.
But really this could keep going,
and we could keep adding isoprene units,
and we'd find lots of nice
plant oils that we make,
and vitamins, but that unfortunately,
is not our goal today.
We're still talking about steroids.
So I'm gonna shift to how our body uses
these isoprene building blocks to create
the chemicals that it needs,
and that's a process
that's called biosynthesis.
So let me clear some room so that
we can talk about biosynthesis.
And in biosynthesis, our body starts off
with isoprene bound to
something called pyrophosphate.
Which looks something like this,
and I'm gonna use the letter R
to represent that isoprene unit for now,
just so I can really show you
what pyrophosphate looks like.
And so that's pyrophosphate,
this green area is pyrophosphate.
And you probably won't be expected
to know too much about pyrophosphate,
but what you should know is
that it's a really weak base,
which makes it a good leaving
group in organic chemistry,
and that's the important part,
because for the reaction
that our body uses
to build with these blocks of isoprene,
it needs a good leaving group,
and that's pyrophosphate.
And our body really begins with
two different isoprene pyrophosphates,
and they're found in nearly
all living organisms,
and those are dimethyl
allyl pyrophosphate,
and isopentyl pyrophosphate.
And I've just shortened the pyrophosphate
to OPP because that's what most
textbooks abbreviate it as,
and it saves quite a bit of time,
but I will go ahead and
write out the names of these.
Just so I don't confuse you too badly.
And those names name pretty
good sense if you've practiced
naming carbon molecules in, say,
an organic chemistry class or something.
But they probably sound like a
foreign language if you haven't,
so let's not get too hung up on them here,
because they don't help us
much with the concept anyway.
But what happens is the
electrons of one pi bond
act like a nucleophile, and
they attack this carbon,
allowing the pyrophosphate to leave,
and that results in a 10-carbon molecule
called gernyl pyrophosphate.
And so that's gernyl pyrophosphate.
And then that process might happen again,
leading to a 15-carbon
farnesyl pyrophosphate,
and for give me if I'm
butchering that pronunciation,
but I'll draw it in.
That's farnesyl pyrophosphate.
And then as these chemical
reactions continue,
our body eventually produces a triterpene,
or if you remember that's
a 30-carbon molecule
made of six isoprene units,
and that triterpene is called squalene,
so let me draw that in.
Okay, just wanted to make sure that
I actually got 30 carbon
molecules in there,
and I think I did, and that is squalene.
It was important for
me to get to squalene,
because this is the molecule
that forms the base of all
of the steroid hormones
that our body makes.
