So speaking of some of the things
found in the plasma membrane,
it has many different types of proteins.
Of the different types of proteins,
there are two main types.
You have integral membrane proteins
which are going to traverse between
the outer and inner leaflet
of the plasma membrane
and go through or integrate
or go through the membrane
and then you have peripheral
proteins which sit either
on the inner or the
outer leaflet of the cell.
These membrane proteins are going to
have a variety of different functions.
There are different proteins
that allow the plasma membrane
to not just separate our external and internal
environments but also have multiple functions
including deciding what
gets in and out of the cell.
So some of this protein functions include
ion chanels which allow certain ions
to be able to cross from outside into the cell
or from inside to the outside of the cell.
The reason why we need these is
because ions are positively charged
and therefore cannot pass
through that fatty acid layer
because of the positive charges
being repelled by the fatty acids.
Another type of membrane protein function that we
find in our plasma membrane are carrier proteins.
Similar to the ion channels, these are gonna
transport substances into or out of the cell
that cannot just pass
through on their own.
A third function of our membrane
proteins are receptor proteins.
Now these receptor proteins are going to do
different things depending on what happens
after whatever is being
received binds to the receptor.
The chemical that binds the
receptors referred to as a ligand
and these ligands bind to the receptor
and either are brought into the cell
or sometimes they may
trigger other reactions to occur.
A fourth function of the
membrane is enzymatic.
So there are several different types of enzymes that
are embedded in our plasma membrane of our cells.
These enzymes are usually
bound by a ligand and then
elicit some type of enzymatic
process after a ligand binds.
And so in this way, we think of our
plasma membrane not just as a barrier
but also something that is actively functioning to
allow certain processes to happen in our cells.
Another function of the
membrane is linker proteins.
Linker proteins are going to link our cells
to other factors inside and out of the cell.
So for example, certain filaments that are associated
with the outside of the cell or our extracellular matrix
require linker proteins so that the cell
is linked to those different filaments.
And another function of the membrane
proteins is cell identity markers.
So everybody has cell identity
markers on their cells.
This is how our body knows that my cells
belong to me and your cells belong to you.
They're as unique to you
as your fingerprints are
and these become very important when
you think about transplant patients.
So for example, if I need a heart transplant
and I get a heart from someone else,
what's gonna happen is the cell
identity markers on that new heart
will not match the cell identity
markers in the rest of my body.
And what happens after that is our
immune system will attack that new heart
because it does not recognize
it as self and therefore,
recognizes it as something that is
foreign and must be gotten rid of.
That is why a lot of transplant patients
must be on immunosuppressive therapy
once they receive a transplant because of our body's
natural defense to anything that doesn't belong.