Now, let's move on to a different type of transmembrane protein that, instead of containing alpha helices, contains beta plepleted sheets. So even though we typically find membrane spanning alpha helices within these transmembrane into a protein, we also actually sometimes contain these beta pleated sheets. So let's discuss a specific example called porin. Now, porin is basically a transmembrane protein that exists in certain bacterial cells, for instance, E. Coli cells, and it exists on the outer membrane of those on the outer layer of the membrane of those bacterial cells. Remember, some cells have actually two membranes and this porn exists on the outer membrane. Now, porin is actually a channel.