By: Frances Kueper and Devika Rao
Introduction
DNA, the blueprint for all living cells, is crucial in the study of biotechnology. Scientists study DNA to design medications, engage in forensic science, and understand the cellular instructions that allow for everyday life—in all of these processes, it is essential that DNA is extracted and analyzed. While DNA extraction may sound like a complex process, this simple experiment will allow you to model the process by using materials already available in your own kitchen.
In this activity, strawberries will be used, as each strawberry cell contains 8 copies of its genome—that’s a lot of DNA! First, an extraction solution composed of water and dish detergent will lyse the cell walls, which are made up of fatty acid compounds. Then, the solution will be filtered, leaving behind cell walls and other “cell junk”. Finally, alcohol will be added to the filtered solution, causing DNA to precipitate out of the solution. After a few minutes, the DNA will appear as a white cloud hovering above the strawberry solution!
Materials
1 Ziploc bag
2 plastic cups
1 coffee filter or cheesecloth
1 small cup
½ cup rubbing alcohol
2 tsp. dish detergent
1 tsp salt
½ cup water
2 strawberries
Instructions
Step 1: First, prep all the strawberries to use for the experiment—that is, remove all the leaves from the strawberries.
Step 2: Place the strawberries into a Ziploc bag, and begin to crush the strawberries. Make sure that most of the air in the bag is let out and that the Ziploc bag is closed before you begin to crush.
Step 3: To make your DNA extraction solution, combine 2 teaspoons of dish detergent, 1 teaspoon of salt, and ½ cup water.
Step 4: To the Ziploc bag with the crushed strawberries, add 2 teaspoons of the extraction solution. This step ensures that the cell walls break open and that DNA is released.
Step 5: Reseal the bag, making sure that most of the air from the bag has been let out, and continue to mash the strawberries for an additional minute. Try not to create soap bubbles.
Step 6: Place a coffee filter (or a cheesecloth) into a separate plastic cup.
Step 7: Carefully open the Ziploc bag and pour the mixture into the filter or cheesecloth. After pouring, gently squeeze the filter so that the liquid in the mixture is expelled into the cup.
Step 8: Slightly tilt the cup, and, aiming for the side of the cup, pour in rubbing alcohol until the ratio of strawberry solution to rubbing alcohol is about 1:1. Do not stir or mix the liquid in the cup. In this process, the DNA will precipitate out of the strawberry solution.
Step 9: After letting the solution sit for a few minutes, you will notice the development of a cloudy white substance that forms in a layer above the strawberry solution. This is your isolated DNA!
Step 10: If you would like to remove the DNA from the cup, use a wooden stick or coffee stirrer to collect the white substance. Congratulations! You have now extracted strawberry DNA.
Visual Instructions:
Sources:
National Human Genome Research Institute home | Nhgri. (n.d.). Retrieved March 14, 2022, from https://www.genome.gov/sites/default/files/genome-old/pages/Education/Modules/StrawberryExtractionInstructions.pdf
Buddies, S. (2013, January 31). Squishy science: Extract DNA from smashed strawberries. Scientific American. Retrieved March 13, 2022, from https://www.scientificamerican.com/article/squishy-science-extract-dna-from-smashed-strawberries/
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