The figure shows a tank for gel electrophoresis. DNA is loaded in the wells and an electric field is applied. Towards which electrode does the DNA move, and why?

Fig. 1: A drawing of a horizontal electrophoresis tank with a gel in the middle. The left end of the tank has an electrode marked P. The wells of the gel, marked Q, are near the left electrode. The gel is marked S. The right end of the tank has an electrode marked R. Four bands of DNA of different sizes are drawn in the gel, and the largest is nearest to the wells.