Gel electrophoresis

Gel electrophoresis is used to separate DNA fragments. Electrophoresis uses an electric current to separate different-sized molecules in a sponge-like matrix. Smaller molecules move more easily through the gel pores than larger molecules.

Agarose gel can be used to separate DNA. First the gel is submersed in a tank filled with a salt solution which conducts electricity.

Using a pipette, DNA samples are loaded into slots made in the gel. The DNA is colorless but a blue dye is added, this makes it easier to track the DNA and its migration through the gel.

The phosphate groups in the DNA backbone carry negatively charges oxygen’s, giving DNA an overall negative charge. In an electric current, the negatively charged DNA moves towards the positive pole of the electrophoresis chamber.

DNA molecules then move through the gel by ‘reptation’-a reptile like snaking action through the pores of the gel. Smaller DNA fragments migrate faster and further over a given period of time than do larger fragments. This is how DNA fragments can be separated by size in the gel.

The introduction of a florescent dye, ethidium bromide, was used to stain the DNA. Ethidium bromide binds to the DNA double helix and glows in ultra-violet light. This lets researchers see where the separated DNA fragments end up.