Gel

Gel electrophoresis is a method for separation and analysis of macromolecules and their fragments, based on their size and charge. The fragments are negatively charged due to the phosphate groups moving them from negative to positive. Smaller fragments move faster than larger fragments because they move more easily through the pores of the gel. Most commonly, the gel is cast in the shape of a thin slab, with wells for loading the sample. The gel is immersed within an electrophoresis buffer that provides ions to carry a current and some type of buffer to maintain the pH at a relatively constant value. The gel itself is composed of either agarose which is extracted from seaweed or polyacrylamide which is a cross-linked polymer of acrylamide.If we add the DNA fragment onto the negative side of the gel electrophoresis than the DNA fragments would move across the gel because of the DNA's phosphate backbones negative charge.