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Southern Blotting

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Edwin Southern invented Southern blotting in 1975 by combining gel electrophoresis with probe hybridization. Southern blotting is an extremely powerful tool used in molecular biology for detecting a specific deoxyribonucleic acid (DNA) sequence in DNA samples and identifying the size of the restriction fragment that contains the sequence. Southern blots have been used to prepare restriction maps of complex genomes as well as looking at the distribution of a gene across a species.

In Southern blotting DNA is extracted, purified, and cut into fragments with restriction enzymes. The DNA fragments are separated by size using gel electrophoresis. The DNA is transferred from the gel to a nitrocellulose filter by placing the gel on top of a sponge sitting in a tray filled with buffer. A nitrocellulose filter is laid over the gel and covered with paper towels. As the paper towels pull the buffer through the sponge, gel, and filter the DNA fragments are carried from the gel to the nitrocellulose filter where they stick tightly. The nitrocellulose filter is removed and hybridized with a radioactively labeled nucleic acid probe that tags the DNA fragments of interest. Unbound probe is washed off and the filter is exposed to X-ray film. The DNA fragments that are
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There is also Western blotting and Northern blotting. Western blotting is used to identify a specific protein in protein samples. Western blotting is generally performed on a SDS-polyacrylomide gel instead of an agarose gel like in Southern blotting. The proteins are transferred to either a nitrocellulose or polyvinylidene fluoride filter and the protein of interest is visualized with an antibody that specifically recognizes it. Northern blotting is a process very similar to Southern blotting that is used to separate ribonucleic acid (RNA) instead of DNA. The RNA in Northern blotting is separated through electrophoresis, blotted, and hybridized with a
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