DNA extraction is a multi-step process by which the genetic material within cells is removed and purified. Analysis of DNA after extraction can be a very potent tool for both medicine and forensics, allowing for identification and comparison of DNA samples as well as screening for various genetic diseases.
Potential
DNA analysis is a powerful tool allowing for the matching of hair and blood samples from a crime scene to suspects. It also can be used in paternity tests and for screening for genetic mutations, as well as in basic laboratory research work. The analysis of DNA is referred to as genomics, and in all cases the DNA has to be extracted from cells in order to perform any sort of analysis.
Identification
The first step of DNA extraction is to "lyse" the cells. Lysing the cell involves breaking down the cell membrane (and in some cases an additional membrane called a cell wall). The cell membrane encases the cell and is responsible for keeping both the nucleus (where the DNA is) and the rest of the cell intact. Rupturing the membrane can be done either by grinding or by sonication. Grinding involves the use of physical force to break the cell membrane, whereas sonication uses high frequency sound waves to punch holes into the membrane.
Function
The second step of DNA extraction is to remove lipids by using a detergent. Lipids are what make up oils, and all cell membranes are made up primarily of lipids, which can interfere with DNA analysis. Detergents that are used are very similar to those used for laundry. By having both a charged and a non-charged end, detergents help break up the lipids into smaller compartments called micelles, which can then be removed from the solution.
Expert Insight
Finally, the DNA is removed from the solution by adding an alcohol, usually ethanol or isopropanol. DNA molecules are insoluble in these substances---the actual DNA material is too charged to be soluble in these relatively non-polar compounds. As a result, they precipitate out, meaning that they are no longer dissolved and instead fall to the bottom of the solution as a solid. Then, the DNA can be extracted using centrifugation---in which a machine spins the tube around very fast, causing the DNA to form a solid pellet at the bottom, which can then be removed. This process will also remove any salts or other substances that can stay dissolved in alcohols.
Considerations
DNA extraction can also be improved by adding a few steps to the process, ensuring purer and higher quality DNA. One danger of extraction is the presence of certain proteins that act to degrade the DNA; addition of agents known as chelators will bind to calcium and magnesium ions in the solution, which is responsible for those proteins' actions. Also present in the original solution are proteins that bind to DNA and can contaminate the sample. These can be removed with proteins that degrade the bound proteins, or by removing them using sodium acetate, causing them to be removed from the solution.
Tags: cell membrane, from solution, proteins that, removed from, removed from solution, proteins that degrade, step extraction