DNA electrophoresis is the process of DNA fragment isolation based on the attraction of that fragment to an electric pole. This process is used to separate DNA fragments based on their respective sizes through a polar attraction across an electrical gradient. Nucleic acids form the rungs of a double helix of DNA, the backbone of which is made up of deoxyribose sugars and phosphates, which gives it a negative charge. Scientists can take advantage of the fact that this negative charge is attracted to a positive electrode through an electric field.
The process of DNA electrophoresis is performed by running DNA across a gel substrate through an electrolytic buffer or substrate such as saltwater. An agarose gel that has been soaked in saltwater can withstand an electrical gradient being passed through it continuously. By making many copies of DNA, usually through a process called a polymerase chain reaction (PCR), a given gene can be exponentially copied from a single occurrence. Genes are physically manifested in DNA segments.
Agarose is a porous substrate that allows small molecules to pass through it. DNA is attracted to a positive charge, so DNA segments of varying sizes migrate through an electrolytic agarose gel inside a saltwater electric field. Large segments migrate through the gel substrate more slowly than small pieces, so the DNA fragments are separated by size. By running a large number of the same size of DNA fragments on an agarose gel, the sample forms a thick band.
DNA electrophoresis requires the use of an electrolytic substrate, an electric field and ethidium bromide, which is a very dangerous chemical. Ethidium bromide intercalates between the nucleic acids on a DNA double helix, and it glows under an ultraviolet (UV) light. To visualize a DNA band on an agarose gel, the gel can be soaked in ethidium bromide and photographed under UV light. The bands formed by different sizes of DNA fragments will be shown, and an experimenter can tell whether the gene of interest — or DNA fragment — is present.
From the smallest organisms, such as bacteria, to the largest organisms, such as whales, species replicate by copying DNA. The code for the creation of proteins necessary for life is written in the genetic instructions provided by strands of DNA. Analysis of DNA is used in many scientific studies, including criminal investigation, genetic studies on animal models, bacterial recombination and peptide classification. DNA indicates the code for protein transcription, so DNA electrophoresis is useful in any situation where a scientist or experimenter would have cause to replicate, separate or examine genes on DNA strands.