When people think of DNA they usually visualize the elegant “twisted ladder” shape seen in everything from advertising logos to Biology textbooks. This visual is actually a kind of artist’s conception. It is a kind of scientific model, useful in helping us understand how DNA functions, but in reality impossible to see.
The structure of a molecule is far too small to be seen with even the most powerful of microscopes. Rosalind Franklin used the process of X-ray crystallography to make an image of the DNA molecule that was used by Watson and Crick to build that first model; but X-ray crystallography is a bit complex for most students to do at home.
Still, some of you might want to do something a bit more dramatic than building a DNA model out of toothpicks and gumdrops. You might not be able to actually see little A,C,T and G pieces, or even a single DNA strand, but did you know that you can use some common kitchen ingredients to extract DNA from your own cells — DNA that you CAN see? First, read this related article: DNA: Definition, Structure & Discovery.
What You Need:
- Small paper cups (You want the smallest sized cups.)
- 1 bottle of colorless sports drink (You can also use a strong salt water solution, but “Lemon Ice” flavored Gatorade tastes better — and you can use the leftovers for refreshments after the lab!)
- Liquid dish soap (You want to use the lightest color or colorless brand you can find)
- A few drops of pineapple juice (You could also try using a quarter-teaspoon of meat tenderizer dissolved in a half-cup of water)
- 1 wood skewer (You want the kind that looks like a very long toothpick. Look in the baking aisle at the grocery store — many people use them to test cakes for doneness.)
- Alcohol (You can use regular rubbing alcohol, but if you can find 91-percent isopropyl alcohol at the drugstore get that. The closer to 100-percent alcohol you use, the better this will work.)
- Narrow container with a lid (You can use a test tube with a stopper if you have one. You could also use a small jar like you buy spices in. Make sure it is clean and dry.)
What to Do:
24 hours before you start, put the alcohol in the kitchen freezer. Don’t worry, it won’t freeze, but it should be ice cold before you do your experiment.
When you are ready, take a good mouthful of sports drink and vigorously swish it around in your mouth like mouth wash. Keep going for at least 2 minutes. This takes some stamina — it’s harder than it sounds, to swish for that long! It also helps if you scrape the insides of your cheeks a little with your teeth. No blood, please; we are after the DNA from your cheek cells, not your blood type!
Spit the sports drink and cheek cell solution into a small paper cup, then pour it into your test tube or spice jar until it is about one-third full.
Add liquid dish soap until your container is about half full. Put the lid on and mix the contents by rocking the container and turning it upside down several times. Be gentle, your goal is to mix the contents but to avoid causing bubbles from the soap.
Add a few drops of pineapple juice or meat tenderizer solution. Repeat the gentle mixing.
Now it’s time to get that icy cold alcohol out of the freezer. Take the lid off of your cheek cell solution and tilt the container in one hand. Use your other hand to very gently trickle a small amount of alcohol down the inside of the jar so that the alcohol forms a layer floating on top of the cell solution. Return the container to its upright position and set it aside for 1 minute.
After a minute, look carefully at the place where the alcohol makes a layer floating on top of the cheek cell solution. You should see a band of white gooey material suspended between the liquid layers. Gently put the skewer down into the container so that the tip touches this material. Carefully twirl the skewer in one direction only; if you are lucky the stuff will wind around the skewer so that you can lift it out through the alcohol layer to look more closely.
- Behold your own DNA!
Why you did what you did:
1. Why did I have to swish so long?
First you had to collect enough cells to work.You are also using the salts in the sports drink to begin to break the cell membrane and the membrane around the nucleus to free the DNA.
2. Why did I use the soap?
Cell membranes are made up of two layers consisting of fats, sugars and salts. The fats are on the inside of the membrane where they can avoid touching the water that surrounds the cell. Detergent molecules have two ends. One end of a detergent molecule is attracted to fat and the other end is attracted to water. When you wash your dinner plate; the fat-loving end of the dish detergent molecule attaches to the grease from your hamburger and the water-loving end attaches to the water in the sink. In the cheek solution, you were using the detergent to move the broken up cell membranes away from the DNA.
3. Why did I use pineapple juice?
Pineapple juice and meat tenderizer both contain enzymes that further help to break down the cell membrane.
4. Why did I use ice cold alcohol?
The DNA was dissolved in the water contained in the sports drink. DNA does not dissolve in alcohol. When the cold alcohol was layered on top of the cheek cell solution the DNA precipitated out of solution.
5. Why did I twirl the skewer?
Remember that famous DNA model. The DNA molecule is a very long strand with a gentle twist. Your visible DNA material is actually many thousands of these strands clumped together. Gently twirling the skewer allowed many of these strands to wind around your skewer like thread around a spool.
6. What else can I try?
Try extracting DNA from fruits like bananas or strawberries. Try leafy vegetables like spinach or kale. Take DNA from seeds like raw nuts or peas. Use about 2 cups of plant material and about half a cup of water and a tablespoon of salt instead of Gatorade. You will probably need to mix it in a blender as swishing that much in your mouth would be kind of hard!
Questions to explore:
- Do you get more DNA from using your cheeks, the fruit, the leaves or the seeds? Why do you think this is so?
- What do you have in common with a banana?
- What happens if the alcohol isn’t cold?
- Are there any steps you can leave out of the procedure and still get results?
- What other sources of DNA could you use? (Please avoid taking samples from the family pet or from your little brother!)
- Could a CSI team use this technique to collect DNA for legal purposes?
- What techniques are used for forensic science or medicine?
More science experiments: