The red blood cell has a very unique shape. It is this squashed bagel-like shape for lack of a better word. Spectrine, which is the twisted polypeptide, it's actually two polypeptides in a helical dimer, running here and there on the inner surface of the red blood cell membrane. Now, the spectrine is not a membrane protein, but is a cytoskeletal protein, a protein that's part of a skeletal framework that's going to give it a solid shape. But it has to be held to the membrane, and it's held to the membrane by attachment proteins. Anchorin is an example of one of these proteins. That is a membrane protein, and that does anchor spectrin to the membrane. So attachment proteins, anchor, spectrin, and also, if you notice, there's an actin molecule, which is also part of the cytoskeleton, and must be anchored to the cell membrane in order for the cytoskeleton to give the cell this shape. It has to exert a force, basically, on the membrane to give it a shape. But otherwise, normally, it'd be spherical, right? The normal low energy configuration, shape of a vesicle is a sphere. So this is obviously not a spherical cell. Glycophore and A is a transmembrane protein. It crosses the membrane with that alpha helical region of hydrophobic amino acids. And its function is to prevent red blood cells from binding to one another. So in a way, it's a kind of a receptor. It's a receptor that says on the surface of one cell says to the other cell, if you're another red blood cell, I don't want to have anything to do with you. It keeps red blood cells from clumping when they're not supposed to to keep your circulation going obviously freely, so that you don't develop blood clots. It's an essential protein, because as we know, there are times when your blood must be able to clot. And under those conditions, something called a coagulation cascade or clotting cascade occurs. Cells, platelets are allowed to form a mesh work and in fact form a clot. But you don't want this to happen with red blood cells that are functioning normally in an organism that has no need of clotting. So Glycophore and A is embedded in the membrane by virtue of the helix. And the portion that it exposes outside the cell is a kind of receptor that is able to look at another red blood cell and say, no binding.