And so the larger DNA fragments, the larger molecules will find it more difficult to move along these pores, while the smaller fragments will find it easier to move along and through these pores because of their smaller physical size and smaller physical weight. So in gel electrophoresis, different fragments are separated on the basis of physical size. The larger molecules are not able to move as quickly as the smaller ones through the pores of that gel. Now, since DNA fragments are all negatively charged, they all move along the same direction. They always move from the cathode, the negatively charged side, to the anode, the positively charged side. And this voltage difference is created because this entire structure is connected to a battery source.