Lipid overview

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- [Voiceover] Let's talk about lipids.

Now for those of you who are familiar with the term

you might associate it with things like fat molecules,

and that would not be incorrect.

Fat molecules are a very common form of lipid,

in fact this is an example of a fat molecule,

or a triglyceride right over here.

Fat or triglyceride,

tryglyceride molecule right over here.

This one in particular is a polyunsaturated tryglyceride

and we have, we have a, go into in depth,

we go into a lot of depth on this

on the video on the molecular structure

of fats slash triglycerides

or on saturated and unsaturated fats.

But you see the tell-tale signs,

you see a glycerol backbone right over here

and three fatty acids, or what were three fatty acids

attached to what was a glycerol molecule.

We go into a lot of depth on that.

But fats are not the only type of lipids.

And so what makes all of these other things

that I'm about to show you also lipids?

What commonality do they have with fats?

Well lipids are just the general term,

the general term for a whole class of molecules

that tend to not be so soluble in water,

that tend to kind of clump up or ball up

when placed in water.

So not, not so soluble,

not so soluble in water.

And I'm being a little bit careful with my words,

I didn't say outright hydrophobic.

There are definitely lipids that are outright hydrophobic,

but there are also some lipids

that have some end of their molecule that's hydrophobic,

but then other parts of the molecule

actually might be hydrophilic.

And there's actually words for that.

So you have some lipids

that are just straight out hydrophobic,

hydrophobic.

They literally try to avoid the water,

they're non-polar molecules, so they just clump together.

But then there's some that have hydrophobic parts

and hydrophilic parts.

And these are called,

and I always have trouble saying this word,

amphi,

amphipathic,

amphipathic molecules.

Where some part is hydrophilic

and some part is hydrophobic.

And we're gonna see that in a few seconds

when we look at phospholipids,

which are crucial for the structure of cell membranes.

And you're gonna see that a lot when you,

when you go into biology.

So what are all these other molecules?

And let's think about what parts of them

might be hydrophobic and what parts might be hydrophilic.

When you look at fats you have this long hydrocarbon chain,

there are any obvious, and there aren't any obvious,

there aren't any obvious charges over here.

In fact, there's aren't any, oxygen is more electronegative,

so you might have a little bit of a partial negative

or partial positive charge.

A partial negative at the oxygen

or maybe a partial positive end at the carbon,

but carbon isn't, is still more electronegative

than say hydrogen,

so you're not going to be able to form

the type of polar bonds that,

the type of, I should say, hydrogen bonds

you would if you had hydroxyl groups here,

if this was an alcohol.

And these hydrocarbon chains over here,

these are very hydrophobic,

so that's what makes fat not be so soluble in water

and clump up with you put it into water.

This molecule right over here,

which we would classify as an ester,

and that's because we have an ester group,

we have an ester functional group right over here

where you have a carbon double-bonded to an oxygen,

and then single-bonded to another oxygen,

and then that oxygen's bonded to a long hydrocarbon chain,

and that carbon is bonded

to a long hydrocarbon chain right over there.

This is clearly going to be hydrophobic.

And this particular molecule

that we're looking at right over here,

this is a major constituent of beeswax.

Of bees, of beeswax.

And if you've even dealt with beeswax,

or really any type of wax,

and waxes in general are considered to be lipids.

You can see they don't, they're not soluble in water,

in fact they're often used to repel water,

to keep water from penetrating into something.

So wax, and in particular beeswax,

and beeswax isn't made up of only this molecule,

this is one of the main constituents,

it has other molecules mixed in there,

but this is also a lipid.

Now what's this thing over here?

This thing I have one six carbon ring,

another six carbon, whoops, I have another six carbon ring,

another six carbon ring, and then I have a five carbon ring.

This is the tell-tale sign,

and let me circle these four rings right over here,

these rings are the tell-tale signs

that we are looking at a steroid,

at a steroid.

And in popular culture steroids have,

you know, you think of steroids as something

that bodybuilders might inject illegally

to pump up their muscles,

but steroids are actually,

when you think about it in chemical terms,

they're actually referring to things

that have this general, these molecules

that have this general structure

where they have this six carbon ring,

this six carbon ring, and another six carbon ring

in this orientation, and then another five carbon ring.

And this steroid that we're looking at,

this has an O-H group attached to it,

so it's actually going to be an alcohol,

so a steroid that's an alcohol

you would call a sterol,

sterol.

And this particular sterol is one that you've actually

dealt with a lot, or at least you've heard about,

this is cholesterol.

So this one in particular is cholesterol.

And cholesterol is often viewed as a negative thing,

people don't, people wanna lower their cholesterol,

but it's essential for life.

It's essential to the functioning of your cells,

and it is a precursor molecule for your steroid hormones,

which make you you.

And this right over here is a steroid hormone,

it's a very well known one.

This is testosterone.

Testos, testosterone,

testosterone, testosterone.

And you see the tell-tale,

you have a six carbon ring right over here,

another six carbon ring right over here,

the double-bond is in a different place

than cholesterol here,

you have a double-bond right over there.

Then you have another six carbon ring,

and then you have the five carbon ring.

And instead of an O-H group here

you have a double-bond, you have a carbonyl group,

you have a carbon double-bonded to an oxygen,

but it actually does still have an O-H group up here.

But this is a derivative of cholesterol,

this is a testosterone, it is a steroid hormone.

This is another steroid hormone.

This is cortisol, cortisol.

Also can be derived from cholesterol.

And you see the tell-tale signs.

You see the six carbon ring,

this has a double-bond right over there.

You see another, you see another six carbon ring,

six carbon ring like this.

It's actually hard to see the double-bond,

so I won't even refer to them,

I'll just refer to the general shape.

So you have a six carbon ring there,

six carbon ring there, six carbon ring there,

and then five carbon, whoops,

and then a five carbon ring just like that.

So once again, they all have this steroid base structure,

but then they all, they also have other parts

that make them different.

For example, that is different than that

is different than that.

And just so you can visualize

these things in three dimensions,

in an actual molecule their not going to look

exactly like this and even talk about what something

in an atomic scale looks like is kind of strange

because light behaves in weird ways,

but you can imagine the molecule would look like this

if you actually, this is kind of a ball and stick model,

well here you're thinking about

what it actually might look like in space

where the white balls are hydrogen,

the grey ones are carbon, and the red ones are oxygen.

So this is also, this right over here,

is what a cortisol molecule would look like

if you think in a space filling visualization.

Now I talked about amphipathic molecules

and phospholipids are probably

the most well-known example of it.

And phospholipids, they have a lot in common

with triglycerides in that you have

this three carbon backbone right over here.

Three carbon, three carbon backbone,

let me do that in a different color.

So you have a three carbon backbone right over here,

so this is a carbon, that's a carbon,

that's a carbon there.

Each of them are attached to an oxygen,

so you can imagine that this

could have been derived from glycerol.

And then two of the carbons,

like in a triglyceride, are bound to a fatty acid like this,

but then one of the carbons, the third carbon,

instead of being bond to a fatty acid

like you have in a triglyceride,

it is bounded to a phosphate group.

So this right over here,

this right over here is a phosphate group.

And this R could just be another chain,

another chain of, another organic chain, so to speak.

But when we talked about amphipathic molecules,

I always have to say it slowly,

so it's a bit of a tongue twister for me.

We're talking about having a hydrophobic end

and a hydrophilic end.

Well what's the hydrophobic end here?

Well this, these, this chains from the fatty acids,

especially the hydrocarbon chains right over here,

these are gonna be hydrophobic.

Hydro, hydrophobic.

While the phosphate end right over here it has charge,

charged molecules dissolve in water very, very well.

And so this one over here is going to be hydrophilic.

It's going to be, it's going to be, I guess you could say

it's going to be attracted to water.

And that's why phospholipids,

and this is just one type of phospholipids,

these chains could be different.

We have a, we have a unsaturated chain here,

and then, a fatty acid chain,

and then we have a saturated fatty acid chain on the left,

and this just actually just made up in this molecule,

but, and they could be different

depending on the phospholipid you're talking about.

But this general property of having a hydrophilic head

and hydrophobic tails make them very well suited

for cellular membranes.

Because you could imagine,

so hydro, that end is hydro,

hydrophilic,

and then you have these hydrophobic,

hydrophobic tails.

Actually, let me see if I can copy

and paste this really fast.

I actually can just draw it really fast.

So let me just draw a bunch of them.

Whoops, nope, I'm having trouble.

Alright, let me just switch back

to my drawing tool.

So let me just draw a bunch of the hydrophilic heads

and then a bunch of the hydrophobic,

whoops, actually I'll draw a few more

hydrophilic heads out here,

and then I'll draw the hydrophobic tails.

Hydrophobic, hydrophobic tails, let me draw them,

draw them really fast.

I'm almost done right over here.

Hydrophobic tails right over here.

And this configuration that I've just drawn

where you have a bilayer of phospholipid,

of phospholipids, a phospholipid bilayer,

this is how cellular membranes are constructed.

Because this you have water,

or things that are very water based

inside the cell, this could be inside,

inside the cell, and this could be outside,

this is outside the cell.

And so the phosphate ends is attracted to the water

and then, but the hydrophobic,

the hydrocarbon tails, those are going to,

they're going to orient themselves in this way

to get away, to get away from the water.

Really they'll just let the phosphate,

the phosphate ends interact with the water.

And so this forms a nice boundary for the cell.

And we're gonna study that thoroughly

as we go more into biology.

So hopefully this gives you more appreciation

of what a lipid is and the different types of lipids.