Well, in gel atrophies all of these proteins in the mixture are forced to move through the porous gel. But in the case of gel filtration chromatography, only the small proteins are actually forced to move through the beads that are composed of that porous gel. In gel filtration chromatography, the large proteins are not forced to move through the porous beads. Instead, they can simply travel through the space around the beads. And because of that, in gel filtration chromatography, it's the larger protein that makes its way down to the column first, because it doesn't experience a large drag force like the small molecules that do travel to the beads do. And so that is the major difference between these two techniques.