Introduction
Isolating DNA From Your Own Cheek Cells
Your DNA is your “genetic fingerprint”—this means that your DNA is like no one else’s in the world!
The procedure that we will use to see your DNA includes the same basic processes that professional
researchers use to isolate, analyze, and manipulate DNA in a laboratory setting (although the DNA
isolated here is not nearly as “pure” as the research lab version).
DNA can be considered the hereditary “code of life” because it possesses the information that
determines an organism’s characteristics and is transmitted from one generation to the next. You
receive half of your genes from your mother and half from your father. Day to day, DNA’s job is to
direct the functioning within the cells of your body.
DNA is in the nucleus of almost every cell in your body. DNA is also located in your mitochondria. The
length of DNA per cell is about 100,000 times as long as the cell itself. However, DNA only takes up
about 10% of the cell’s volume. This is because DNA is specially packaged through a series of events to
fit easily in the cell’s nucleus. The structure of DNA, the double helix, is wrapped around proteins
called histones, folded back onto itself, and then supercoiled into a compact chromosome.
Individual chromosomes can be studied using microscopes, but the double helix of a chromosome is so
thin that it only be detected through innovative, high-tech procedures. Chromosomal DNA from a
single cell is not visible to the naked eye. However, when chromosomal DNA is extracted from multiple
cells, the amassed quantity can easily be seen and appears as strands of mucous-like, translucent
material.
We will first collect cheek cells by swishing a sports drink in our mouths and using our teeth to scrape
cells off our cheeks. (The more vigorous and the longer that you swish, the more cells are removed,
and the more materials you’ll have from which to extract DNA.) Then, we will lyse the cell membranes
by adding a detergent based cell lysis solution, which allows the DNA to be freed. DNA is soluble in
water, but much less soluble in alcohol. Thus, alcohol will be slowly added, DNA will precipitate (rise)
to the sports drink/alcohol interface, and you will be able to see your own DNA! The white, stringy
material is thousands of DNA molecules stuck together (with some histones too).
Materials
Per person:
 1 10 mL test tube
 1 small cup of sports drink
 1 wax pencil to label your test tube
Per table:
 1 small beaker to transfer lysis solution
 1 small beaker to transfer chilled ethanol
 1 graduated cylinder to measure lysis solution
 1 stopwatch
Procedure
1. Read the entire procedure before beginning please, so you can pace yourself and work organized
and efficiently.
2. Label your 10 mL test tube with your initials using the wax pencil.
3. Obtain a small cup of sports drink and swish it around in your mouth for 1 full minute. As you
swish, gently and continuously scrape the sides of your cheeks with your teeth to help release your
cheek cells.
4. Carefully spit the drink (with your collected cheek cells) back into the small cup.
5. Pour the contents of the cup into your labeled test tube (discard the cup in the trash please).
6. Obtain a small amount of cell lysis solution from the front counter using your small beaker. At your
lab station, measure 2 mL of cell lysis solution into a graduated cylinder.
7. Holding your test tube at an angle, carefully add the 2mL of cell lysis solution to your test tube that
should already contain your collected cheek cells.
8. Place your thumb over the end of your test tube and gently invert your test tube test tube 5-8
times, while holding your thumb over the top.
9. Place your test tube in the test tube rack and allow it to stand for 2 minutes. Now would be a great
time to read the introduction if you haven’t yet!
10. Using the other small beaker at your table, obtain enough cold ethanol so that when you add it to
your test tube, the contents will reach the bottom of the blue label on the test tube. Add the cold
ethanol by letting it gently run down the inside of the test tube (hold the test tube at an angle). You
should now have 2 distinct layers. DO NOT mix the cheek cell solution with the alcohol!
11. Watch as wispy strands of translucent DNA begin to clump together where the alcohol layer meets
the cheek cell solution. (It may resemble cobwebs extending upward.)
12. Place your test tube in a test tube rack and let it stand undisturbed for 15 minutes. During this time
the DNA will continue to precipitate out. If you don’t know what precipitate means, I would read the
introduction. Use the remainder of your time to review for your Unit 7 Exam.
13. After the 15 minutes are up: On your own sheet of notebook paper that you will later answer your
post-lab discussion questions on, create a diagram that shows how your test tube looked at the end
of the 15 minutes.
14. Clean up please, before you answer the discussion questions. The discussion questions will be
posted on our class website if you run out of time to finish them.
Discussion Questions
Please answer these questions on your own sheet of paper. Show off your high school level thinking
skills!
1) The cell lysis solution contains salt and dish detergent. The detergent used is a dish detergent that
contains lipases and proteases. What type of biological molecules are these? Prove it!
2) What do you think the function of the detergent is, and what do you think would happen if you did
not add the lysis solution? Explain your reasoning please.
3) Why do you think that adding the cold alcohol was included as a step in the procedure? How might
your outcome be affected if you skipped this step?
4) How does this way of looking at DNA differ from the diagrams of DNA you may have seen in the
book or models of DNA you may have built in middle school? Is it what you expected? Explain.
5) Looking at the amount of DNA you collected, how do you think it is possible for these long strands
to fit into the nucleus of a single cheek cell?
6) Based on your understanding of precipitation, how did adding the alcohol help your DNA to appear?
7) How did your results compare to those of your partner? If somebody did not get the expected
results, what might be some sources of error you can think of?
8) What is your “take away” from this lab? In other words, what do you now understand about DNA or
the process of DNA isolation?
Additional Notes
 The recipe for the Salt/detergent mixture is: 2 L distilled water, 100 mL detergent (we use
Palmolive dishwashing detergent), 15 g salt.
 The ethanol needs to be ice cold--keep in freezer until the time it is needed.