Gel Electrophoresis

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Gel electrophoresis is a technique used to separate nucleic acids (DNA fragments) and proteins in a gelatin-like material using an electrical field. DNA is negatively charged and in an electrical field DNA moves towards the positive electrode. The distance travelled by fragments depends on mass and size. Smaller fragments move faster and further towards anode while larger fragments move slower and over shorter distance. This technique is commonly used by forensic scientists to assist in the identification of criminals from forensic evidence and for paternity testing. Genetic fingerprinting makes use of the fact that our DNA contains repetitive DNA sequences also known as short tandem repeats (STRs). These are present at multiple sites in the DNA and the number of repeats at each site varies between individuals. Thus, the scientist uses this technique to determine the number of repeats at any given locus in a sample of DNA. In the process of DNA profiling, DNA is extracted and purified from a sample of cells or tissue of the individual. It is then amplified using Polymerase Chain Reaction (PCR), which is a technique used to clone and amplify to produce many copies of a piece of DNA. The DNA is then digested with one or a few restriction enzymes. These restriction enzymes cut the DNA at their restriction sites and produce numerous fragments. Gel electrophoresis is subsequently used to separate the fragments according to their size and charge. The fragments are visualised by staining them with Methylene blue or Ethidium Bromide/UV light. Thus, this is how DNA patterns are observed for DNA fingerprints [1][2][3]

An animation on the process of gel electrophoresis

References:

  1. http://www.sumanasinc.com/webcontent/animations/content/gelelectrophoresis.html
  2. http://www.life.illinois.edu/molbio/geldigest/electro.html
  3. Bradley, Philip, and Jane Calvert. "Genetic Fingerprinting." Biology: For the Medical Sciences. Second ed. Print.


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