why DNA fragments separate according to size in an electrophoresis gel?

Answer 1

DNA fragments are negatively charged, each DNA fragment moves down the gel at a rate that is inversely related to its size, becaus the attraction forces between the anode and the small fragments are much greater than that of anode and large fragments. So small fragments will be closer to the edge of the plate near the anode ,while large fragments are seen far away from it.

Answer 2

Imagine a child and an adult trying to climb through a jungle gym that's a tangle of pipes and beams. The child will go through it faster, because the child is smaller. It's the same with gels. The DNA wants to move through the gel, because it's negatively charged, and the gel has a charge. Smaller DNA moves quickly though the gel, large pieces more slowly.

Answer 3

the electrophoresis gel works like a seive. It has tiny spaces throughout for the particles to travel in the field. The smaller pieces will travel faster because they easily fit into the spaces of the gel. The larger pieces don't pass through as easily, and therefore take longer. So, smaller objects will travel quickly, whereas larger ones will be slower. I hope that makes sense.

Answer 4

This incorporates the theory of diffusion. In a medium, regardless the physical state, substances travel in a certain velocity relative to their size. Lighter DNA fragments travel faster as they are light and present less obstruction due to the friction against the gel and also due to the defiance to gravity.

Answer 5

Its like shaking marbles of different sizes in a large container. They tend to arrange themselves by size (bigger, heavier marbles falling to the bottom).