They are pulled by the force of gravity. So as they travel, those tiny proteins, the green proteins, will travel slowest because they have to travel through the tiny pores of those beads, while the red proteins will travel slightly quicker, because sometimes they get stuck inside the beads. And have to travel through the beads. But other times, they make their way around the beads, and so they will be found somewhere in the middle as compared to the green, which will be found at the top. Now, these large proteins essentially never make their way into those beads because they simply cannot fit into the internal volume of those beads. And so what happens is they will emerge first, they will be found at the bottom relative to these two other proteins.