|Extraction of DNA from Cheek Cells
February 29th 2013
DNA, deoxyribonucleic acid, is the genetic material of every living organism and is found in the nucleus of eukaryotic cells. DNA is often called the ‘blueprint for life’ because it contains the necessary information to carry out all the living processes of the cell (1). The purpose of this lab was to extract DNA from human cheek cells. The isolated DNA could be used in mapping or sequencing, PCR, crime scene investigation or other downstream applications (2).
MATERIALS AND METHODS
To extract DNA from cheek cells, 3 mL of water was added to a labeled, 15 mL tube. The inner lining of the cheek was then chewed for approximately 30 seconds. The 3 mL of water was used to rinse the mouth for 30 seconds, after which the water and the cheek cells were expelled back into the 15 mL tube. Using a plastic transfer pipet, 2 mL of lysis buffer was added to the tube containing the water with the cheek cells. The tube was then capped and gently inverted 5 times to lyse the cells.
Five drops of protease and salt solution were added to the sample. The tube was capped and inverted 5 times. The sample was incubated in a water bath at 50°C for 10 minutes. Following incubation, 10 mL of cold ethanol was slowly added while holding the tube at a 45° angle. The tube was placed upright at room temperature for five minutes, after which the sample was inverted 5 times. The DNA extraction protocol and all materials and reagents were provided by Bio-Rad (2).
Throughout the experiment, numerous observations were made. The water containing cheek cells was white or cloudy in appearance. Upon addition of the lysis buffer and protease, the solution became clear. A white precipitate was visible following the addition of cold ethanol.
Extraction of DNA from cells is a relatively straight-forward and simple process. It is routinely carried out in laboratories and has numerous downstream applications, including sequencing and PCR.
Only a few reagents were used to extract DNA from cells: lysis buffer, protease and ethanol. Lysis buffer broke open the cheek cells to expose DNA and cellular proteins. This explains why the sample in this experiment became clear upon addition of the lysis buffer. Protease served to enzymatically break down the proteins in the sample. Maximum activity of the enzyme was achieved by incubating the sample at 50°C. Finally, DNA became visible as a white precipitate after adding cold ethanol. Extraction of DNA was successful following this protocol. The DNA sample can now be purified for use in future experiments.
1. Russell, Peter J. 2010, iGenetics: A Molecular Approach, San Francisco: Benjamin Cummings Publishers, 3rd Ed.