DNA Extraction

Why is it necessary to extract the DNA out of a cell in genetic engineering? As mentioned above, DNA is found in the nucleus of a cell. In order for genetic engineers to be able to work with and transfer DNA into another organism, it must be first taken out of the cell. Fortunately, a DNA molecule remains somewhat stable outside of a living cell allowing scientists the opportunity to work with and study it without destroying it. To extract DNA, tissue samples are taken from plants, and crushed to break open the cells.

The plant tissue must be ground with a mortar and pestle to break the plant cells open allowing the DNA to freely leave the cell. (Image by P. Hain)

Next, a buffered salt water solution is added into which DNA dissolves easily. The DNA is purified by adding an organic solution into which other molecules, such as fats and proteins dissolve. The purified DNA solution is separated off and the DNA is precipitated out of the solution by adding alcohol. The DNA is now a solid string that can be spooled out with a hook. The extracted DNA is placed into test tubes with a weak buffer solution and can be stored almost indefinitely.  

Extracted soybean DNA after it has precipitated out of solution. (Image by P. Hain)

During DNA extractions, the entire cells' DNA is extracted at the same time. Extracted DNA has usually been sheared into smaller pieces due to the leaf tissue grinding process. This makes it difficult to isolate an entire chromosome in once continuous strand. However, large pieces that contain several to dozens of genes can be extracted intact with this method. After isolating the DNA, researchers can use it for further laboratory studies including genetic engineering.