DNA Extraction – The Foundation Of Molecular Biology

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DNA extraction refers to the isolation and purification of DNA from biological samples.  The first extraction was done by Frederick Miescher, but the process has since been optimized and standardized for quality, yield and speed.  Many companies now sell their optimized chemicals for DNA extraction in kits, comprising of protocols and reagents.  However, the basic chemistry has remained the same for most of the kits.   The chemistry of DNA extraction involves:

Cell lysis

This encompasses mechanical grinding and/or chemical, or enzymatic digestion of the starting material.  Usually, this step requires an amphipathic lysis buffer.  Detergents or chaotropic agents can serve this purpose. The lysis buffer interacts with and degrades the amphipathic cell membranes, thereby releasing the cell constituents into the buffer solution.  The mechanical grinding, if required, can be done using a mortar and pestle, or a homogenizer, but similar results can be achieved by enzymatic digestion.

DNA purification

Following lysis, the DNA needs to be separated from every other cell constituent.  This can be achieved by a sequence of precipitation and washing steps – DNA is precipitated out of solution and thereafter washed to further remove impurities.

In a review article, Tan and Yiap (2009) curated protocols for nucleic acid extraction with a historical perspective; from the basics to the cutting edge. The protocols were grouped under conventional methods and solid phase nucleic acid extraction.  The article also appraised the strengths and limitations of the different protocols reported.

Conventional Methods: (1) Guanidium Thiocyanate-Phenol-Chloroform Extraction (2) Alkaline Extraction Method (3) CTAB Extraction Method (4) Ethidium Bromide (EtBr)-Caesium Chloride (CsCl) Gradient Centrifugation.

Solid Phase nucleic acid extraction: (1) Silica Matrices (2) Glass Particle (3) Diatomaceous Earth (4) Magnetic Bead-Based Nucleic Acid Purification (5) Anion-Exchange Material


Sources

Dahm, R. (2005). Friedrich Miescher and the Discovery of DNA. Developmental Biology. 278: 274-288. Retrieved from www.elsevier.com/locate/ydbio

Tan, S. C., and Yiap, B. C. (2009). DNA, RNA, and Protein Extraction: The Past and The Present. Journal of Biomedicine and Biotechnology. 2009:574398 doi:10.1155/2009/574398

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