How Proteins Anchor Themselves in the Membrane

00:00 Many of these proteins have to embed themselves in the membrane, somehow they all have to embed themselves in the membrane, somehow.

00:09 The first type we can see is much like we saw with the proteoglycan but we're linking directly to a phospholipid.

00:18 So the phospholipid becomes modified such that the head is associated with a protein.

00:24 And then that phospholipid is anchoring the protein that's external to the cell inside the membrane.

00:33 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.

00:45 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.

01:15 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.

01:30 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.

01:54 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.

02:08 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.

02:18 I'll ask you for a second though to review our protein structure.

02:22 What level of protein structure are we discussing here with alpha helices and beta pleated sheets? Secondary structure is what we have.

02:33 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.

02:47 We could indeed have quaternary structure if there were additional proteins with tertiary structure associated to form this whole channel.

02:58 So that would mean more than one polypeptide chain.