And then the protein channels, the other type of transmembrane proteins used for transport, can use these electrochemical gradients to basically move the molecules down the gradient without using any type of energy source. So essentially, these membrane pumps use energy to establish these gradients and then the channels don't have to use energy because they use these electrochemical gradients to move the molecules in a natural and spontaneous direction. So there are two categories of membrane pumps. We have these Atpas and we have these secondary transporters. In this lecture we're going to focus on ATPases. Now, Atpas themselves can also be broken down into two classes.