Pre AP Biology
DNA Extraction Lab!!!!!!
Background: DNA is found in living cell. Globular DNA is about 6 feet long in each human
nucleus. You will be trying to extract your DNA from your cheek cells. You will use
Gatorade to help remove cells from the surface of your cheeks. Detergent contains a
chemical (SDS) that lyses (breaks) cells. It essentially breaks down the phospholipid
bilayer of the cell membrane. Proteins break down at around 55⁰C and DNA denatures
above 85⁰C. You will hopefully obtain some DNA so you can see what it looks like.
Lab equipment: 2 test tubes test tube rack stirring rod pipet
1. Place 10 ml (about a cm) of Gatorade in the bottom of small cup.
2. Put the 10 mL of Gatorade in your mouth and swish vigorously for 1 minute. Spit the
Gatorade/spit back into the cup. EEEEWW
3. Carefully pour the “cheek cell solution” into a clean test tube. Do not fill your test tube
more than 2/3 full. Throw your cup away in the garbage.
4. To the same test tube, add 1 mL of 25% liquid dish soap solution.
5. Stopper the test tube and then mix the contents by gently inverting the test tube several
times. Try not to create a lot of foam.
6. Place your test tube in a 55-60 degree Celsius water bath for 5 minutes.
7. When you have 1 minute left of heating, measure 5 mL of ice cold 95% ethanol (ethyl
alcohol) into a second clean test tube. This needs to stay cold!
8. After the 5 minute waiting period, remove the first test tube from the water bath.
9. Holding the first test tube at an angle, slowly and carefully pour the ethanol down the
side of the first test tube so that it forms a layer over the “cheek cell water” mixture.
10. Wait for about 5 minutes, watching what happens at the interface between the water
11. You may obtain your DNA by spinning a glass stirring rod in the test tube. The DNA may
stick to the glass rod.
12. If you would like to keep your DNA – suck your DNA up into a pipet and the put it in a
small microtube. Cover it with ethanol.
13. Now you may start the clean up process. Since your spit (yuck) is in the test tube, please
thoroughly clean the test tube using a brush, a small amount of diluted dish soap, and a
test tube brush. Rinse the test tube thoroughly, and then put it back in your tray. Also,
wash your glass stirring round and return it to your tray.
14. Clean your lab table off with soap water.
Post- Lab Questions:
ANSWER ON A SEPARATE PIECE OF PAPER – YOU CAN TURN ONE IN FOR 2 PEOPLE!
1. Where is DNA located in a cell?
2. What two main types of molecules make up the cell membrane and the nuclear
3. Keeping in mind the components of the cell membranes, what role do you think the
soap played in the extraction process?
4. Why did you heat your saliva/detergent to 55⁰C? Why not 100⁰C?
5. Compare the densities of the water mixture to that of the alcohol used in this lab.
6. Based on your observations, does DNA appear to be soluble in alcohol? Why or why
7. Why do you think it was so easy to obtain cheek cells?
8. How are plant cells different from animal cells?
9. How might the extraction of DNA for plant material differ from the extraction of DNA
from animal cells?
Scientists often use a protocol, such as the instructions given in this activity, as a starting point
for developing or improving techniques. There are several DNA extraction protocols available.
Some of the protocols, for example, include the addition of an enzyme along with the
detergent. Working with your partners, develop a list of questions that could be the starting
point for experiments to improve the DNA extraction protocol used in this lab. Come up with a
minimum of 2 questions – you cannot use the following – but may expand on them.
Does the addition of an enzyme, along with the detergent, increase the quantity of DNA
Does the addition of an enzyme, along with the detergent, change the time required for
the DNA extraction?
Does the cheek cell protocol work for extraction DNA from plant Material?
CONCLUSION: What did you learn? What could be improved?