So it turns out that there’s one more lipid that we need to pay attention to
with particular detail because it’s a critical component of all cell membranes.
It’s the phospholipid.
The phospholipid is very similar to a triglyceride.
Even in these fatty acid tails could be kinky or they could be straight.
We have a glycerol and then, we have our fatty acid tails.
But in addition, we have a substitution
for the other fatty acid tail that we see in a triglyceride,
we now have a choline and a phosphate group added on.
So what happens here is we have the head region which is polar and it is hydrophilic.
It’s because it’s polar, you recall water is a polar molecule,
the water and the hydrophilic head of the phospholipid like to be together
and then the non-polar tails, their fatty acid tails, there’s no polarity in there,
they are hydrophobic which means they are water hating,
phobic, they don’t like water.
And so they want to stay away from water as much as possible.
And so we have a couple of neat formations that happen because of this.
Before we go on, we’re going to change our notation a little bit.
First of all, you can see,
there’s a number of different ways that we might depict our phospholipids.
The one all the way over on the right
is the one that we’ll pretty much see from now on out
where we have the hydrophilic head and then we’ll have the hydrophobic tails.
So the neat thing about phospholipids
is if you were to put a few in a jar of water and shake it up,
you would see that they would make this micelle formation
in which they hide the hydrophobic tails away from the water,
and the hydrophilic heads act to kind of protect those.
Now, there’s movement between them
but they in general will hold this micelle formation
and it’s this micelle formation that actually, our detergents take advantage of
so that we can hide little packets of grease inside with the hydrophobic tails
and get them away from our dishes.
Now, another formation that we might see
or in fact we do see a lot is the phospholipid bilayer.
It’s less likely to happen when you shake up some phospholipids in a jar
but it happens all the time in nature to form cell membranes
as well as some of the cell organelles.
So we’ll see that the hydrophobic tails go in towards each other
and that’s because of the nature of the cellular environment.
We have an aqueous environment, the tails don’t like water
so they associate with each other and then, the phospholipid heads
which are hydrophilic are okay with being near the water.
So all membranes are composed of this phospholipid bilayer.
We’ll have some endomembrane organelles that we’ll look at in the future
and even the nucleus is bound with phospholipid bilayers.
So in conclusion, in this lesson,
we should have learned how to describe the four levels of protein structure
as well as explain how nucleotides come together to form DNA and RNA molecules
with a specific attention on that three prime and five prime thing.
In addition, we are able to now discuss the major classes of phospholipids
and perhaps, you’ll even be able to explain to your friends
why butter is a much better choice than margarine.
So thank you so much for watching and I look forward to seeing you in our next lecture
where we’re going to explore membranes in much more detail.