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- [Voiceover] Lipids are one of the four

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major macromolecules.

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So lipids themselves though
are insoluble in water.

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If you mix oil and water,
I don't care how much you

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shake it around.

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If you let it sit again,
that oil will separate

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from the water.

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Now there are three major
classes of lipids here.

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And all three of 'em are
gonna be insoluble in water.

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We have the triglycerides.

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Now these are mostly energy
based, kind of help store

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energy in your body.

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We have the phospholipids.

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These phopsholipids are
important because they make up

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a majority of your cell membrane.

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So think of every cell in your body.

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Those millions and millions
and millions of cells.

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The phospholipids are what
make up the majority of

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the membrane that covers
them, which keeps them intact.

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And then you have steroids.

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These are gonna be a lipid that is based

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on a ring structure.

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Now these aren't the
steroids you think of as

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the illegal steroids from sports.

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It's just steroids that
everyone has in their body.

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There are things like cholesterol,
estrogen, testosterone.

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Those are steroids.

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So steroids, this particular
type is a form of a lipid.

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We'll start with the triglycerides.

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Now more commonly, the
triglycerides are known as fats,

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or they're known as oils.

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These triglycerides are made
up of two main molecules,

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glycerol and fatty acids.

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But the triglycerides, tri means three.

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Triglycerides have three fatty acids.

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Now these fatty acids
can either be saturated

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or unsaturated.

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In the case of saturated
fatty acids, which is where

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the term saturated fats comes
from, saturated fatty acids,

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a lot of times you'll see in
solid form at room temperature.

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They're a kind of fats.

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Every chemical bond is filled up.

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But in the unsaturated fatty
acids, this is where your

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unsaturated fats or
unsaturated oils come from.

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The unsaturated fatty acids do
not have every chemical bond

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filled up.

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They potentially could form more bonds.

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And these triglycerides
are primarily gonna be

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an energy stored molecule.

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So if you have lipids stored
in your body for long term

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energy use, a lot of times
they're stored as triglycerides.

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So here's an example of how
the triglycerides are formed,

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and then two different types.

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In Figure A on the left you're
seeing, you have the three

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yellow structures.

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Those are your saturated fatty acids.

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You can see every carbon
has four bonds off it.

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Every (mumbles).

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It's just one over another.

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And the top oval, the glycerol.

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What ends up happening here
is you can see how there is

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an OH that is highlighted in blue.

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And then another H on the glycerol.

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Well if you take off the HOH,
or H2O, by removing water,

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that's dehydration synthesis.

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You could make a new molecule.

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Do that three times.

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You bind three saturated
fatty acids there, and now

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you have a triglyceride
with your B in the middle.

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But if you end up having a triglyceride

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which is unsaturated, that's
C on the right-hand side.

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You can notice how that
as you go down those

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fatty acid chains, sometimes
there's a carbon carbon bond.

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But instead of one line,
meaning a single bond, there is

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two lines, which causes the
line to kind of angle out

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a little bit.

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That means you could
technically add some more bonds

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in there if you wanted
to, some more hydrogen.

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So we have our triglycerides.

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Saturated, the middle is B.

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Unsaturated fatty acids
is the right, letter C.

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The second main category of
lipids is your phospholipid.

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Now the phospholipid still
has the same glycerol.

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It still has fatty acids.

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But now there's only two fatty acids.

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The 3rd fatty acid has
been switched as now

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a phosphate group.

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At the term phospholipid,
you have a phosphate group.

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Two fatty acids all attaching to glycerol.

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Now what's unique is
one end of this molecule

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is water soluble,
hydrophillic, water-loving.

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But remember I said all
lipids are insoluble.

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That's still true because
the other end of the molecule

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is water insoluble,
hydrophobic, water-fearing.

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So even though a portion
of this phospholipid could

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be soluble in water, the other
portion is still insoluble

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in water.

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So overall, that means the
molecule cannot fully be soluble

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in water.

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So your phospholipid.

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Their function, cell membrane.

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They form the cell membrane
of practically every cell

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in your body.

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Now it's not the only piece
of a cell membrane but

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the large component of the cell membrane.

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So here is your phospholipid.

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You can see the top sphere,
which is referred to as

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the polar head, is comprised
of your glycerol molecule

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and the phosphate group.

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But coming off the other side
are the two fatty acid chains.

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Now these two fatty
acid chains, one happens

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to be saturated.

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One happens to be unsaturated.

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So which one's which?

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As you're looking at the
screen, is the left-hand one

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the saturated or unsaturated?

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The one on the left, which
has the term fatty acid

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pointing to it, that's
the saturated fatty acid.

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The one on the right-hand side
of the screen, where you have

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the bracket that says
nonpolar, you can see there's

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a double-bonded carbon
in the middle there.

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That means that's the
unsaturated fatty acid.

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And to round off the
category of lipids, we have

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our steroids.

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Now all these steroids are
composed of four carbon rings.

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What makes these different
from your carbohydrates

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is these rings are
actually sharing a side.

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You can see other rings
when you trace them.

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They both have one side that
is shared between each ring.

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The carbohydrates do not share.

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There's always a bond in
between each monosaccharide,

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or each ring.

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So always as four carbon rings,
and always as sharing sides.

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The example you see here, cholesterol.

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Now think of it as a
whole, cholesterol's bad.

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Not necessarily.

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You have to have some
cholesterol in your body

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to function normally.

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Now sure, if you have too much
cholesterol, it could cause

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a problem.

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We have to have some there to help with

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structural supports of your
cell membrane and to help

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with other normal cell functionality.

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Your body naturally produces cholesterol.

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The question is does it
produce the right amount?

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Or unfortunately, could
it be producing too much?

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This producing too much of
this, then we've got a problem.

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Estrogen, testosterone.

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And what's even more interesting here is

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the cholesterol molecule
can head down and split

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and be converted into
estrogen and testosterone.

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So cholesterol is actually
kind of a starting material,

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which helps produce the male
sex hormone, testosterone,

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and the female sex hormone,
estrogen, your steroids.