- [Instructor] Hi, in previous videos,
I introduced steroids
to you as one example
of the chemical messages
that our body parts
use 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 a 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.
And so 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 it 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 tetraterpene.
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,
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 isopental pyrophosphate.
And I've just shorted
that 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 make pretty good sense
if you've practiced naming
carbon molecules in say,
in 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 a gernyl pyrophosphate.
And so that's gernyl pyrophosphate.
And then that process might happen again,
leading to a 15 carbon
farnesyl pyrophosphate,
and forgive me if I'm
butchering that pronunciation,
but I'll draw it in.
And 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.
