So now that we know that proteins play a major role in forming biological membranes, in this video we're going to introduce the different types of membrane proteins. Now, really, there are 2 main types of membrane-associated proteins, and we have those 2 listed down below. Now, the first are the integral membrane-associated proteins, and the second type are the peripheral membrane-associated proteins.
Now, the integral membrane-associated proteins, as their name implies, are non-covalently integrated into the phospholipid bilayer as we can see down below. And usually, these integral membrane proteins span the entire lipid bilayer, so that they have an extracellular portion and an intracellular portion. And so, of course, this purple protein that we see down below is our integral membrane protein, and again, we can tell because it's completely integrated and spanning our phospholipid bilayer.
Now, the next type, the peripheral membrane-associated proteins are at the perimeter of the lipid bilayer, and they do not span the entire lipid bilayer like integral membrane proteins do. And so notice down below in our image, this blue protein right here is on the periphery or on the perimeter of the lipid bilayer. And so this is going to be our peripheral membrane-associated protein.
Now, there is a subcategory of peripheral membrane-associated proteins, and those are the lipid-linked membrane-associated proteins. And so again, the lipid-linked membrane-associated proteins are peripheral membrane-associated proteins, so they're going to be found on the periphery. But really, what makes these lipid-linked ones so distinct is that these are peripheral membrane proteins that are covalently anchored to lipid groups within the bilayer. And of course, if you have a protein that is covalently linked to a lipid group, that's going to make it a lipoprotein. And so these lipid-linked membrane-associated proteins are peripheral lipoproteins.
And so, if we take a look at our image down below right here, notice we're showing you a lipid-linked membrane-associated protein here. And notice that it is indeed on the periphery, and the protein is not really spanning the membrane like our integral membrane protein was. Instead, it is on the periphery, so that makes it a peripheral membrane protein. But also notice that it's covalently attached to this lipid group that we see right here, and that is really what distinguishes it as its own subcategory within the peripheral membrane proteins.
Now, as we move forward in our course, we're going to talk even more details about each of these different types of membrane-associated proteins. But for now, this here concludes our introduction to the types of membrane proteins, and I'll see you guys in our next video.