So what are some of the proteins that we see in
transmembrane group of proteins in the membranes.
So some of them act as channels.
Here we have a channel that's simply open channel.
It allows passage of molecules through the membrane.
So recall that the internal environment of the membrane
is hydrophobic. And it is much wider than the hydrophilic heads.
So any molecule that is particularly large or hydrophilic
has a really hard time making it through that phospholipid bilayer
because of the large lipid component in the middle.
So anything that is pretty charged or polar or large
needs a channel protein in order to get into a cell.
So we have protein transporters.
We will see that we also have enzymes embedded in the membrane.
So these enzymes may receive a signal on the outside
and then cause something to happen on the inside,
such that when the signal arrives on the outside,
we've one molecule come in and is converted into another molecule.
by that enzyme embedded in the membrane.
Often these enzymes are protein kinases
and we'll introduce those later in the lecture.
Another type of membrane protein we have are receptors.
We have an extracellular receptor here
where a ligand, or a communicating molecule will bind to that
and cause an effect inside the cell
and we'll certainly explore a number of different mechanisms for
these sort of receptor proteins that are embedded in the membrane.
Also we could have our identity markers.
So this is proteoglycans, this is a little bit of a closer look.
We have a membrane embedded protein
with a glucose chain or polysaccharide attached to it.
So proteoglycans help the cells identify themselves to other cells.
They're sort of like saying "Hey, I'm a red blood cell
and I belong in this body. Are you cool?". "I'm cool
And we all belong together". They may be involved in
recognizing each other so they can actually stick together.
And say "Well, I'm tissue of the liver
and I'd like to be with tissue of the liver".
So those identity markers are really critical for cells
to understand what other cells that are near.
The other sorts of things we might have are proteins embedded in
the membrane that are involved in holding other cells together.
Imagine if you had cells in your gut
that actually weren't held together at all
and there was just space between them.
So things could pass freely between the cells.
That wouldn't make any sense because
you need the cells in the gut
to be actually digesting the foods that you eat
and gaining nutrients out of them.
So many of these embedded proteins will be about
cell cell adhesions, cells sticking to each other.
We also will see cytoskeletelal attachement proteins.
So, soon we're going to look at some of the
cytoskeletal elements, the skeleton of the cell.
And we have to anchor those skeletal element somewhere,
much like our muscles are anchored to our skeleton
in order to keep our body up on the bones,
we have to anchor these things in the cell membrane also.