[Narrator] - So kind of simply put a lipid...
a lipid is a molecule that will dissolve into
an organic solvent.
So we've got an organic solvent,
let me draw this organic solvent,
and a lipid is a molecule that will dissolve
into this organic solvent.
And this is a kind of unique definition
in the organic chemistry world,
because most classes of molecules
contain either a similar functional group
or have a similar structure
like carbohydrates have a specific ratio
of carbon, oxygen and hyrdrogen
and proteins have an amino group
and a carboxylic acid group
with a carbon side chain and so on,
but lipids are classified more
by the shared physical property.
So when I say that lipids dissolve
in organic solvents again non-polar,
as opposed to water, so non-polar,
what I'm really pointing out
is their non-polar nature
and this is mostly attributed
to a lot of carbon-carbon and carbon-hydrogen bonds.
So carbon-carbon bonds, and I'll do these in orange,
Lots of carbon-carbon bonds,
and then carbon-hydrogen bonds as well,
and I'll do these in white.
Lots of carbon-hydrogen bonds here.
And because these carbon atoms and hydrogen atoms
aren't particularly polar there isn't
a particular place where electron density is pulled to,
so it's really spread out across this whole chain,
and that makes this chain
of carbon and hydrogen sigma bonds...
let me write that in, sigma bonds...
particularly kind of non-polar
and sets up this class.
Now even though this class of lipids...
write that again, lipids...
are a little more loosely defined than others
lipids are a large enough group
that they can be broken down into smaller categories
and probably the best place to start breaking them down
is by whether or not they're hydrolyzable
so a big $2 word there, hydrolyzable,
hydrolyzable or not, not hydrolyzable.
And what hydrolyzable means is that
things can be broken down
so broken down, lyzed, broken down
by the addition of water, or hydro.
So by adding water we can break these into smaller units.
And that's kind of a good break point
in the bigger class of lipids
and probably the most talked about
of the hydrolyzable lipids are triglycerols.
I suppose they get the most attention
because they're the most abundant of lipids
but with triglycerols fundamentally what you have
is a glycerol, a glycerol is a three carbon chain,
three carbons bound to three hydroxyl groups.
Each one has a hydroxyl group,
so each of these has a hydroxyl group.
That's glycerol, and attached to glycerol
we have three fatty acid chains.
One at each of these separate carbon hydroxyl groups.
And remember that a fatty acid is
a carbon-hydrogen chain, an R group,
that is capped at the end of the chain
with a carboxylic acid functional group.
That's what a fatty acid is.
So we've got a carboxylic acid functional group
at the end here.
So we've got three of these,
let me draw that in real quick.
Sorry I know this is a bit tedious
but let me get these drawn in real quick here.
And these are going to be attached
at each of these carbon and hyrdroxyl groups
at this glycerol, so let me put a plus sign
and then I'll kind of show you
what this ends up looking like all put together.
So we've got our 3-Carbon back bone
and then each is attached via an ester,
so this is kind of an ester group right here
we've got a carbon bound to an OR group
and then double-bonded to this oxygen right here
and then that's the R of our chain here
so each of these is attached to a fatty acid.
And so you can see that the product
is a triester made of three fatty acids
so triester made of three fatty acids
bound to a glycerol backbone, so a triglycerol
and if all of the fatty acids are the same
so if they all have the same kind of R group
at the end we have a simple triglycerol
and if they're different
we have a mixed triglycerol.
Now triglycerols as a group of hydrlyzable lipids
gets further broken down into
saturated and unsaturated.
So let me clear some space here
and show you what I mean.
We've got saturated
and unsaturated.
And to show you what I mean here
let me draw a carbon chain really quickly
for this saturation concept.
So I've got a carbon chain,
and I'll kind of show it going on
in both directions there with a little arrow.
I've got this carbon chain and
in this carbon chain my carbons are
linked to a carbon in front of them
and a carbon behind them,
and what that does is it leaves each carbon
with two bonding electrons, and so
if those bonding electrons are taken up by hydrogen,
so with hydrogen here drawing in my hydrogens,
if all of those carbons are bound
to as many hydrogens as possible
then this carbon chain is saturated with hydrogen,
saturated with hydrogen atoms.
And you can also see that this chain
is full of single bonds, or sigma bonds.
Now if it's unsaturated,
let me draw another carbon chain here,
if it's unsaturated there's a carbon,
or multiple carbons really,
that are bound to less hydrogens
than their maximum.
So they're bound to less than two or so hydrogens,
so let me show you why that might be.
So I've got a carbon bond here,
and then if I have a double bond to this carbon
and keep going, then what I've created
are a couple carbons here, this one and this one,
that can only bind one hydrogen
because carbon can only bond to four different atoms
it only has four bonding electrons.
So this carbon has as many hydrogens as possible
and these two carbons have as many hydrogens as possible.
This last one on the end would have three hydrogens
but this carbon right here is bound to one less hydrogen
because it's double bonded to this carbon.
So this carbon chain is unsaturated,
and you can kind of associate that
in the context of a fatty acid
with having pi bonds.
This is a pi bond, a double bond.
Because these double bonds
in naturally occurring fats
are always in the cis or z position
they cause little kinks in the chains.
We've got kind of a kink going on in this chain.
And what happens is that makes it harder
for these unsaturated triglycerols to pack together
and it results in a lower melting point.
Or in other words these melt with less heat.
So typically unsaturated triglycerols
are liquid at room temperature
and we call them oils.
So unsaturated triglycerols are oils.
And that's different than you can see
these saturated triglycerols
which can pack together a little more tightly
with their straight chains
and they take a little more heat then to melt.
So typically these are solid,
the saturated are solid at room temperature
and we call these fat.
So an example of oil might be olive oil,
and a good example of fat is really,
of this saturated fat might be
something like butter,
butter is a solid at room temperature.
It just kind of has a little fun fact.
If you were trying to make
an unsaturated fat into a saturated fat,
say you were want to make a liquid fat
into a solid fat you'd want to saturate it
you can do that by hydrogenating this bond,
or by adding hydrogen and heat,
which is going to break this double bond
and allow you to add on an additional hydrogen.
And that's a process that the food industry
actually uses pretty frequently for various reasons.
When you do that you make some
artificial double bonds in the process
which result in transbonds all naturally occurring.
Unsaturated fats are in this cis orientation
and when you artificially hydrogenate them
you actually end up with a couple of trans,
trans double bonds and that's actually the process
that results in trans fat production,
and trans fats are the fats on food labels
that you typically try to avoid
because of their harmful effects in the human body,
but that's just kind of a little fun fact aside,
that's where trans fats come from.
Now in a cell the main function
of triglycerols are energy source.
Let me draw a cell, got a cell with a membrane
and a nucleus and some little cell parts here.
And the main function of triglycerols
are energy, energy storage.
And what allows triglycerols to function
as energy storage is the fact that they're
chock-full of carbon and hydrogen bonds
which are perfect for combustion reaction.
So what you have essentially is an alkane
just like, say for example, iso-octane,
which is in gas, and alkanes are great
for combustion reactions
just like combustion reactions that power your car.
So for example if you have an alkane
like the simplest one would be CH4 methane
plus oxygen, two oxygens is going to give you
some carbon dioxide gas and some water,
but most importantly is going to give you heat energy.
So that's where the energy comes from
in the form of fats.
Just like the combustion reaction in your car
that's creating power, and in fact
that's why you hear about some cars
being converted to run on vegetable oil.
Because vegetable oils have lots of alkanes
that are perfect for this combustion reaction.
So in our bodies triglycerols store
about nine kilocals of energy,
so nine kilocals which is more energy
than even carbohydrates or proteins store.
They each store about four kilocals,
so really one of the main functions
in our body of triglycerols,
which are a type of hydrolyzable lipids
is energy storage.