We place the funnel on top of a long, narrow column, and inside that column, we pack that column with these insoluble gel beads. Now, in the case of affinity chromatography, what we want to do is we basically want to modify those gel beads and we want to attach a specific type of group or molecule onto those gel beads. For example, if we zoom in on one of these gel beads, we get the following diagram and notice that to the gel bead. 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.