Hi. It's Mr. Andersen and in this podcast I'm going to give you a brief
overview of the cell membrane. You probably learned growing up that the function of the
cell membrane is to regulate what comes in to and what goes out of the cell. It's over
simplifying it a little bit. But it's a pretty good definition. And so you may ask yourself,
why do you have a picture of a muskox here? Well the reason why is that when I ever talk
about the cell membrane I like to talk about the muskox and how it's a whole heck of a
lot like this over here. This thing over here is called a phospho. And the reason it's phospho
is because we have a phosphate group right up here in the head. It's called a phospholipid.
And the phospholipid basically has two parts to it. Up here it's going to have a charged
part. So it's going to have a negative charge up here. And then the tail end, this lipid
part, or that's a fat part, since it has so much carbon carbon carbon with hydrogen around
the outside, it's non polar. This whole rear end is going to be non-polar. What does that
mean? Well this end over here loves water. And this end down here hates water. You know
that if you have put oil which is similar to a lipid in structure in water it just doesn't
mix. And so basically the head is going to love water. The tail is not. We call a molecule
like this amphipathic. And so basically why is this like a muskox? Well, if you throw
a bunch of muskox together. And then you have a predator show up. The heads of the muskox
are going to face the predator. Because the heads of the muskox love a fight. And they
want to fight that predator. Now the tail of a muskox is going to protect the baby muskox
that are going to sit on the inside. And so basically they'll form a ring around whatever
they want to protect. And that's because a muskox is amphipathic. We look at those phospholipids.
Then they're going to be the same way. In other words the heads are all going to face
the water. And then the tails in here are going to be away from the water. And so what
you get is a membrane. This would be a single layer of phospholipids. This would be a bilayer
right here. And so basically all the cells, period, all the cells that we have have a
cell membrane. And all of those cell membranes do the same thing. They regulate what comes
into and out of the cell. Now the model we use to explain how a cell membrane works is,
it is a fluid mosaic model. So let me get a color that you can see. So it's a fluid
mosaic model. If we breakdown this word, it's fluid. And that means that all the material
inside the membrane is actually moving around. And if it ever stops moving, then it doesn't
function as a membrane. And the other thing is that it is a mosaic. And so it's made up
of a lot of different things. What are the major things that it's made up of? Well you
can see, here's those phospholipids. Those are forming this membrane. But the big blue
things are going to be proteins. And so the two major parts of a membrane are going to
be the phospholipids which are the red things. And then we're going to have proteins. What's
the function of the phospholipids? Those basically keep water on either side. And so it makes
the structure. What's the function of the proteins? Well those actually give proteins
their specific characteristics. And so it allows the material in. It connects to material
outside. And so to get your heard around this, the cytoplasm is going to be down here. So
this would be the cytoplasm. And this is going to be the cytoskeleton. And it's attached
to it. And then the extra cellular fluid is going to be on the outside. Now there are
a few other things you can see inside here. We've got this folded protein. We've got,
right up here, I can see this right here, is called, let me get rid of some of that.
This is called a glycoprotein. Glyco means that it's got protein on the inside. But it
also has a sugar attached to it. We're going to have glycolipids. We're going to have a
number of things. Like here would be cholesterol. But basically when you're thinking about a
membrane, the function of it is to keep material on either side. And it has to maintain its
fluidity. And so all of these things are moving. These phospholipids are moving horizontally.
They're floating around. And I've seen some neat animations of this. Think of it as like
a sieve. This thing is floating and all of those proteins are like floating around inside
of it as well. Now its attached to the cytoskeleton and to the outside, to the extracellular matrix.
But it's really influx. And then the characteristics are going to come from the proteins. What
it does. So if we talk more about that phospholipid itself, the phospholipid, again has a hydrophilic
head. Has a hydrophobic tail. And they float back and forth. If they get too close together
that's bad. And so what they lots of times will have is a kinky tail. An unsaturated
lipid tail. And that kind of keeps them apart. Sometimes if it gets too cold, the cholesterol
will actually keep them from getting too close. And if it gets to warm, as they start to drift
apart the cholesterol will kind of hold on to it and keep it there. But the function
of this is to allow the movement of materials. So oxygen needs to get into a cell. It's going
to do that through diffusion. And carbon dioxide is going to get out. So what actually moves
through a cell? Well the only things that can really move through a cell are going to
be things that are uncharged. Or things that are really, really small. But really things
that are uncharged. And so how does oxygen get in? It can diffuse because it doesn't
have a charge. Carbon dioxide out the same way. But even things that are water that are
really really small, they can't get in. Or glucose can't get in. It actually has to move
through proteins. And so what do proteins do? Proteins allow material into and out of
a cell. So we'll talk more about how this actually works. But how does water get into
a cell then? We used to think that it would just flow in using osmosis. But we now know
that you have these proteins called aquaporins. And basically what they do is they will allow
water to move through. It moves through really, really quickly. But sometimes we'll make proteins
that actually have this area on the inside where it's protected. And that allows the
material to move through that has any kind of a charge. So that would be like glucose
moving through here. And then we have some of them that will move through using a process
of active transport where we put energy in to move them apart or facilitated diffusion.
So we've got a lot of different things going on. But if you can remember that a cell membrane
is in all cells. It's fluid. It's always in movement. And it's really made up of two things,
phospholipids and proteins, you've got a pretty good start. And I hope this is helpful.