We basically attach a specific type of group we're going to call group Y. Now, what type of group that we want to attach? Well, the type of group we want to attach basically corresponds to that substrate molecule that the protein that we want to actually isolate binds to it. And to see exactly what we mean, let's take a look at the following diagram. So let's zoom in onto the molecular level to a small section of this column. We basically get the following diagram.