• All about Genomic DNA Purification

    Genomic DNA makes up the total genetic information of an individual. In genetic analysis, forensic investigation, food safety, biotechnology, and other diagnostic purposes, DNA may need to be extracted from its varying sources to remove the organic and inorganic compounds that may interfere with the process. When DNA is properly isolated, it can have a higher quality and a longer storage life. The process of extracting DNA from its cellular base is known as genomic DNA isolation or purification.

    DNA can be isolated from a variety of sources, such as blood, hair, sperm, bones, nails, tissues, urine, fossil, bacteria, animal tissues, and plants. When purifying genomic DNA, laboratories consider several factors, such as the source of the DNA sample, age, and the size. Another considerable factor is whether the DNA sample is fresh or has been stored. Scientists make sure that the method they are using is efficient enough to purify the DNA.  A different isolation method is used for stored samples, such as the DNA coming from archived tissue samples, frozen blood, or exhumed bones from ancient human.

    In the process of separating DNA from its cellular components, laboratories follow four stages, which include disruption of DNA, lysis, removal of proteins and contaminants, and recovery of DNA.  In some instances, DNA disruption and lysis can be combined. Lysis can be done in a variety of ways. The easiest method used by laboratories is to incubate cell lysates at high temperature for about 20 minutes. Another method to carry out lysis is salting out, wherein a high concentration of salt is added to the sample in order to precipitate the contaminants. DNA lysis can also be done through organic extraction method, which involves the use of detergent mixed with phenol, chloroform, and isoamyl alcohol. Another lysis method used is known as cesium chloride (CsCl) density gradient, wherein scientists use toxic substances to purify DNA through centrifugation. The CsCI method is a complete opposite from the Anion-exchange technology – a method that only depends on the interaction between the negatively charged phosphates under low-salt conditions. With the ingredients and other precipitating substances added during the lysis, scientists may remove proteins and contaminants as they precipitate from the sample by centrifugation. As a result, DNA is recovered through alcohol precipitation.

    Today, with the presence of commercial DNA purification kits, genomic DNA isolation has become easier.  The silica-based method provides a simple and reliable purification technique for high-quality DNA based on selective absorption of nucleic acid. Silica-based method is inexpensive and is suitable for all types of applications (i.e. Southern blotting, PCR, real-time PCR, RAPD, RFLP, and AFLP analyses). Many commercially available DNA purification kits include contents that allow rapid DNA purification, such as a pH buffer known as tromethamine, ethylenediaminetetraacetic acid (EDTA) for ion bonding, and a detergent known as sodium dodecyl sulfate (SDS).

    DNA purification can also be done at home using different household appliances and chemicals. For food safety, anyone may separate contaminants from meat by homogenization with salt and water. This method can also be useful in the case of tracing the origin of food poisoning outbreak, wherein food experts extract DNA through the precipitation of proteins with the use of alcohol or any other tenderizing ingredients, such as pineapple juice.

    www.qiagen.com/literature/…/pdf/1017778_benchguide_chap_2.pdf

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