DNA…you hear about it all the time. Scientists and lawyers to help in criminal investigation, paternity suits, cloning, etc use DNA every day.
Your DNA is your “genetic fingerprint”—this means that your DNA is like no one else’s in the world! Although this is true, over 99% of our DNA is identical. It is the slight differences or our DNA that makes a big difference and makes us unique. The procedure that we will use to see your DNA includes the same basic processes that 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 is a nucleic acid. The building blocks or monomers of nucleic acids are called Nucleotides. Nucleotides are made of 3 basic parts; a deoxyribose sugar, a phosphate group, and a nitrogen base. There are four different nitrogen bases they are Adenine, Thymine, Guanine and
Cytosine. Adenine (A) always bonds with Thymine (T) and Guanine (G) always bonds with Cytosine (C). The sequence of nitrogen bases is like a language or a code used to store and share information throughout the cell. This is much like letters in an alphabet are a code that are used for people to store and share information. The DNA code is 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. DNA is often referred to as the “boss or brain of the cell”, this is not true. DNA is not the boss of the cell; it is merely a storage molecule for information.
DNA is more like a blueprint used to build a building. After the building is built, the blueprint is not needed for the building to function. But as things breakdown the blueprint is use for maintenance or if an identical building is to be built.
DNA is in the nucleus of every cell in your body that contains a nucleus.
(Red blood cells do not contain a nucleus). 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, folded back onto itself, and coiled 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 looks like strands of mucous-like, translucent cotton.

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 meaning it dissolves (
) into water much like salt dissolves into water. In alcohol DNA is not as soluble. Thus, alcohol will be slowly added, and
DNA will precipitate (
) 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 proteins too). In each human cell there are only 46 complete DNA molecules (
) therefore it requires many cells before the DNA will be seen.
Materials
1 15mL test tube
1 role of tape for labeling
1 small paper cup filled with Gatorade © for swishing
2 ml of lysis solution: 2 L distilled water, 100 mL detergent (we use Palmolive dishwashing detergent), 15 g salt.
5-10 ml of ice-cold alcohol
1 small pipette for transferring
Procedure
1. Label your 15mL test tube with a piece of tape and your initials
2. 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.

3. Spit the drink (with your collected cheek cells) back into the small cup.
4. Pour the contents of the cup into your labeled test tube (discard the cup).
5. Holding the test tube at an angle, use the provided plastic pipet to add 2mL of cell lysis solution to your collected cheek cells.
6. Cap your test tube, and invert it 5-8 times. (This mixes the lysis solution with the cheek cells.)
7. Allow this to stand for 2 minutes.
8. Using the provided pipet, add the cold alcohol by letting it run gently run down the side of the test tube (hold the test tube at an angle) . Add the alcohol until your total volume reaches 12-13mL. You should have 2 distinct layers. DO NOT mix the cheek cell solution with the alcohol!!!
9. Watch as wispy strands of translucent DNA begin to clump together where the alcohol layer meets the cheek cell solution. (It kind of looks like cobwebs extending upward.)
10. Place your 15mL 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.
11. Optional —use a plastic pipet to transfer your DNA into a smaller test tube. To do so, place the pipet near the DNA and draw the DNA into the pipet (along with some alcohol).
Do not move your pipet up and down into the bottom layer.
Discussion Questions
Thoughtfully answer the following questions.
1. What are 3 parts of every nucleotide that make up DNA?
2. What are the 4 different nitrogen bases found in DNA?
3. What is the shape of DNA
4. What is the function of DNA from day to day?
5. Describe how long strands of double-helical DNA fit into the nucleus of a single cheek cell.
6. What was the purpose of using the cell lysis solution?

7. Why does the DNA become visible once the alcohol is added?
8. If DNA is so thin, how is it that we are able to see it during this simple lab exercise?
9.
Why do you think DNA is referred to as your genetic fingerprint?
10.
If a DNA molecule is found to be made of 30% Adenine, what are the individual percents of
Thymine, Guanine, and Cytosine.
11.
Consider the picture of the check cell in the beginning of the lab. The 5 um means 5 micrometers and is a measurement of length. 1 meter contains 1 million micrometers.
*What is the diameter of the cheek cell in micrometers?
*What is the diameter of the nucleus of the check cell in micrometers?
* How many Cheek cells would span from one end of a meter stick to the other?
12.
How many nucleotides are in the DNA molecule at the beginning of the lab?
13.
Blood cells are not made like most of the other cells in our bodies, by basic cell division; instead they are made in the red bone marrow found in our large bones such as the femur in the leg. When blood cells are first developing they contain a nucleus but as they mature the nucleus breaks down to allow the cells to have more flexibility so they can move through the extremely small blood vessels known as capillaries. If red blood cells do not have a nucleus how do they know how to function? (Think of the blueprint analogy)
14.
Since mature red blood cells do not contain a nucleus and therefore do not have any DNA, why would blood at a crime scene be useful as “DNA evidence”?
15.
Why would there be 92 DNA molecules in a human cell as it prepares for cell division instead of
46?