Extracting DNA Experiment
Materials:
2-3 tablespoons of dish soap (preferably uncolored and unscented, so you will see a better effect)
2 cups of tap water
2-3 teaspoons of table salt (NaCl)
1-7 large strawberries with the stems removed.
3-4 tablespoons of hand sanitizer (preferably 70% alcohol or higher)
Ziplock bag
Strainer
Spoon or chopstick
2 transparent glasses (preferably big)
Steps:
Place the hand sanitizer in your fridge so that it will be cold when you need to use it.
For the soapy-salt solution, fill your first transparent glass with water, add 2-3 tablespoons of dish soap, and then add 2-3 teaspoons of table salt. Stir everything for a couple of minutes (if you're using colored dish soap, stir until the color is uniform).
Take your strawberries and put them in a zip lock bag. Squish them until you don't feel or see any large pieces.
Open your zip lock bag and pour in the soapy-salt solution that you prepared before.
Close your zip lock bag and continue squishing the strawberries for a couple of minutes to mix the solution in.
Prepare the second transparent glass and your strainer. Pour the solution you have in your zip lock bag into the glass through the strainer. (You can do it multiple times to get rid of all the solid strawberry parts)
Now take the cold hand sanitizer from the fridge and pour some into the solution while stirring it.
As you stir it, you will begin to see white foam on the top of the solution. This is the strawberry DNA you just have extracted! (If you do not see the foam, you are welcome to add more hand sanitizer!)
Explanation:
The reason why we squished the strawberries was to break their outermost layer - a rigid cell wall. By breaking that cell wall, you are exposing the inner strawberry cells because they have nothing to protect them.
When you mix the strawberry mush with the soapy-salt solution, the dish soap in that solution dissolves the phospholipids - the components of the plasma membrane (the second outermost layer after the cell wall) - and the nuclear membrane (what surrounds the nucleus of a cell).
Phospholipids consist of two parts: the hydrophilic or "water-loving" heads and hydrophobic or "water-fearing" tails. They arrange themselves into bilayers, where the heads are on the outside in order to react with water and the tails are on the inside, hiding from it. Soap has a similar structure to the phospholipids, so it enters the membrane and damages the phospholipid bilayer, which causes the membrane itself to burst open and expose the DNA we want to extract.
During the process of squishing strawberries in the soapy-salt solution, we do not see the DNA because it dissolves in water. Salt neutralizes the DNA’s charge and makes the molecules less hydrophilic (less "water-fearing"), making it easier to precipitate the DNA in the alcohol from hand sanitizer.
DNA is insoluble in alcohol, especially when salt is present. By adding the hand sanitizer to the solution, it causes the DNA to precipitate. DNA comes out of the solution, clumps together, and becomes visible!
Photo Credit: lobestir.com
About the Author
Margarita Shestereva- CuriouSTEM Staff
CuriouSTEM Content Creator- Biochemistry
