Many of these proteins have to embed themselves in the membrane,
somehow they all have to embed themselves in the membrane, somehow.
The first type we can see is much like we saw with
the proteoglycan but we're linking directly to a phospholipid.
So the phospholipid becomes modified such that
the head is associated with a protein.
And then that phospholipid is anchoring the protein
that's external to the cell inside the membrane.
Or the protein could be inside the cell.
So either way, they're not transmembrane proteins,
they're just associated with
the phospholipid bilayer on either side.
So peripheral proteins often anchor
using the phospholipid attachment
but these transmembrane proteins
have to actually cross the membrane
and so the amino acid arrangement in these proteins
has to be such that they have hydrophobic amino acids
in the domains that's spanning the membrane. We may see
some proteins that are associated with the membrane,
with the single alpha helical coil.
And we may also see things like channel proteins where you have
multiple alpha helical coils associated with each other
in order to form either a channel or
a receptor protein across the membrane.
Again, we have to keep in mind that
the central region in the phospholipid bilayer,
the amino acids of those polypeptide chains have to be hydrophobic
and then the ones that we see in red would have to be hydrophilic
because they're out in the environment where there's lots of water,
the aqueous environment internal and external to the cell.
Another way that we can associate proteins in the membrane,
for example for making a larger channel
or a pore which things can move through,
we might see beta pleated sheets association.
So we've got beta pleated sheets and beta pleated sheets
in this protein that then has further levels of folding
in order to create this protein channel.
I'll ask you for a second though to review our protein structure.
What level of protein structure are we discussing here
with alpha helices and beta pleated sheets?
Secondary structure is what we have.
And then also you can see in these membrane channels or this pore
that there is certainly tertiary structure
in which we have not only beta pleated sheets but also other loops
and coils in order to create this channel through the membrane.
We could indeed have quaternary structure
if there were additional proteins
with tertiary structure associated to form this whole channel.
So that would mean more than one polypeptide chain.