Discover some of what makes you YOU!
What you will need:
- Bottle of clear or lemon-lime sports drink
- Liquid dish soap (preferably a light color)
- Pineapple juice or meat tenderizer powder (¼ tsp dissolved in water)
- Wooden skewer or toothpick
- Rubbing alcohol
- Narrow, tall container like a test tube or spice jar with a lid
- Eye dropper or pipette
- Small paper cups, 3 oz.
Here’s what to do:
- Two or more hours (up to a whole day) before the experiment, put your rubbing alcohol in the freezer to chill. The alcohol should be ice cold when you use it.
- Make sure your container has a lid and both the container and lid are clean and dry.
- If you have recently eaten, rinse your mouth out with some water. We want to extract DNA, not food chunks from your teeth!
- Take a drink of the sports drink, but don’t swallow! You don’t want your mouth too full because you want to be able to move the liquid around. Swish the liquid around in your mouth, like mouthwash, for at least 30 seconds. Your cheeks may get tired, but keep going!
- Spit the liquid into your container until it is about one-third full. The sports drink should now contain some of your cheek cells!
- Add liquid dish soap until your container is one-half full. Cap the container and mix the solution by carefully swirling the container around or by turning it upside down and right side up for 2 minutes. *You don’t want to shake the container too long or too hard because it may break the DNA strands.* If you start to see a lot of soap bubbles, you’re probably shaking the container too hard.
- Add a couple drops of pineapple juice or meat tenderizer solution and mix again, gently.
- Retrieve your rubbing alcohol from the freezer.
- Take the lid off of your container. Hold the container in one hand and tilt it (at least 45 degrees). With your other hand, carefully trickle up to 2 teaspoons of the cold rubbing alcohol down the side of your container. The alcohol should form a layer on top of the soap and cheek cells solution.
- Carefully, tilt the container back to upright and let it sit still on the counter for at least 1 minute. At this point, do not shake or disturb your container.
- Look at the interface between the two layers in your container; this is where the alcohol layer touches the soapy sports drink layer. Do you see some white gooey stuff there? Gently poke your skewer or toothpick into your container and through the interface. Slowly twirl the skewer in circles a couple of times to collect the gooey material.
- Lift the skewer up through the alcohol layer and out of the container. These white gooey strands are strands of your DNA! What do they look like? How long are the strands you extracted? What does your DNA feel like?
- You can save your DNA in a clean container or alcohol or dry it out and keep it like a souvenir.
Take it further:
- Do you get more DNA if you swish the sports drink in your mouth longer (like 1 or 2 minutes)? What about if you swish for half of the time? Do you still get DNA?
- Can you get more DNA at the end if you rub the inside of your cheek with a cotton swab or finger before you swish the sports drink?
- If you can, try the experiment again with a more concentrated alcohol, like 91% rubbing alcohol. Does the experiment still work?
- Try the experiment again with strawberries or another fruit or vegetable. (See links at the end of this article for help.) Which produces the most DNA?
- Does all DNA look the same? Why do you think that is? Read more about DNA to discover the answer. What do humans have in common with a strawberry or banana?
- Test different variables in the experiment to see if you can improve the extraction yield (end up with more DNA). What happens if you swish with salty water instead of sports drink?
- What if you use a different detergent? What happens if you skip the pineapple juice or meat tenderizer?
- Does the experiment still work if the rubbing alcohol isn’t cold?
What’s going on?
All living organisms contain DNA, deoxyribonucleic acid. DNA lives inside the nucleus of most of our cells and gives us the code of life; it tells our cells how to develop and function. In this experiment, we extracted DNA from our cheek cells. Do you think the white gooey material we extracted is what a strand of DNA looks like in a cell? One strand of DNA is actually microscopic, meaning we can’t see it with just our eyes. So what is the white stuff we looked at? It is a bunch (think millions and more) of DNA strands tangled together!
In this experiment, each ingredient played a role in getting the DNA out of the cheek cells. The sports drink has salt in it that provides a suitable environment for the cells, begins to break apart proteins in the cell, and later, helps the DNA separate from the other cell components so we can see it. If you saw chunks fall to the bottom of your container, that was proteins and other cell fragments clumping together with the help of the salt. This makes the DNA solution a little cleaner. Dish soap molecules have one end that attracts water and one end that attracts fat, so the soap molecules attract both fats and water away from the DNA. This further helps break down the cell membranes and extract the DNA from the nucleus of the cell. Finally, the pineapple juice or meat tenderizer contains enzymes that finish breaking down the cell membranes.
At this point, we have DNA and a bunch of other cell parts and proteins and saliva floating around in a solution that is mostly water; this is called an aqueous solution. The cold alcohol is poured down the side of the container because we don’t want it to mix with the solution. DNA is soluble, or dissolves, in water, but it is insoluble in alcohol, so the DNA that touches the alcohol at the interface