DNA Extraction from Cheek Cells
Developed by The New York Hall of Science, modified by Science Museum of Minnesota
(Adapted from a protocol by Judy Schleppler, SUNY Stonybrook)
This is an activity that we have used with visitors for many years. It is a very easy procedure but one in which not all visitors will successfully isolate their own DNA. Those visitors who vigorously swish and remove lots of check cells will see some DNA, while others just don’t collect as many cells and will not be able to see the DNA strands. We have noticed those individuals who are chewing gum, or have just eaten will not be as successful in extracting DNA. We think they have swallowed all of their available cheek cells and so do not have as many available for extraction. Regardless of the result, many visitors enjoy attempting to extract their own DNA sample. We often let them take home their sample in a small microfuge tube, especially when this activity is carried out as part of a classroom activity. One word of caution, however, saliva is used in this activity, so all tubes, tips and cups should be disinfected either by autoclaving or rinsing in a 10% bleach solution.
- 50 ml tube with cap
- liquid hand soap in a pump dispenser
- plastic disposable pipet
- squeeze bottle
- glass stirring rod
- 1.5 ml microfuge tube
- Dixie cups
- tap water
- containers for disposing of cups, tubes, plastic pipets and stirring rods
- alcohol for precipitating DNA
- extra microfuge tubes (if samples are to be taken home)
Collect cheek cells
- Swill 5 ml of water in your mouth for 30 seconds. It is better if you vigorously swish the water back and forth across your mouth.
- Spit the water and cheek cell mixture back into the Dixie cup, and then pour the mouth wash into a 50 ml tube.
The swishing washes cells from the inside of your cheeks into the water. More vigorous swishing washes more cells off and yields more DNA. We are also washing bacterial cells from the inside of the mouth, so will isolate their DNA as well.
Release DNA from inside the cheek cells
- Add one pump of liquid detergent.
- Cap the tube and mix the contents by gently inverting several times. Do not shake the tube or you will get lots of foam.
The detergent removes the greasy cell membranes from around the cheek cells (and bacterial cells). The cheek cells also have a membrane around the nucleus, which is also removed. The cell contents (including the DNA) are released into the detergent solution.
Precipitate the DNA
- Remove the cap and carefully add 4 ml of 95% alcohol using the squeeze bottle. Place the tip of the alcohol bottle against the side of the 50 ml tube and dribble the alcohol into the tube. The alcohol should layer on top of the mouthwash solution.
- Hold the tube still for 1 minute. Look for the clouds of white, cottony strands of DNA forming between the alcohol and salt water layers.
DNA is not soluble in ethanol, so it precipitates where the ethanol and salt water layers meet. Most other cell materials remain in the salt water layer. Bubbles displaced from the salt water get trapped in the DNA strands and make them easier to locate. Single DNA molecules are way too small to see-a strand seen here is probably a clump of thousands of DNA molecules.
Collect the DNA
- Drop a glass rod into the tube and let it rest on the bottom.
- Wind the DNA onto the rod by turning it in one direction. If you stir the rod in the tube, the DNA may stick to the rod. If the DNA does not stick to the glass rod, use a plastic pipet to carefully remove your DNA.
- Scrape the DNA into a small microfuge tube and add alcohol. You can take this home if you like. For long-term storage of your DNA, store your tube in a freezer.
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