In gel electrophoresis, why do smaller DNA fragments travel further than larger ones?

In gel electrophoresis, the movement of DNA fragments through the gel matrix is influenced primarily by their size. Smaller DNA fragments can navigate through the porous structure of the gel more efficiently than larger fragments. The gel itself acts as a molecular sieve, where the pores provide resistance to the movement of larger molecules. As a result, smaller fragments encounter less friction as they maneuver through the gel, allowing them to travel further in a given amount of time compared to larger fragments.

While it's true that DNA is negatively charged and is attracted to the positive electrode, it is the size and ability to move through the gel that primarily dictates the distance traveled. The concept of density, while relevant in some contexts, does not directly affect the movement of DNA in this case. Thus, the characteristic that enables smaller fragments to travel further is fundamentally their ability to move more quickly through the gel's structure.