Strawberry DNA – Food Science
In this lab, you extract and isolate DNA from strawberries using simple, household ingredients.
You’ve probably learned or heard about DNA, but have you ever seen it? With the Strawberry DNA experiment, you’ll extract, isolate, and observe the DNA of a strawberry in a matter of minutes. It sounds impossible, but thanks to special characteristics of strawberries, it’s actually very possible… and simple. You don’t have to be a geneticist and you don’t need an electron microscope. It’s easy, fun, and all you need are some household materials.
- Isopropyl alcohol (5 mL)
- Dish soap (10 mL)
- Salt (1/4 tsp)
- Zipper-lock bag
- Water (90 mL)
- Measuring cups and spoons
- Small glass container
- Pipette (optional)
Put a bottle of isopropyl alcohol in a freezer. We’ll come back to it later. Measure 6T (90 ml) of water into a small glass container.
Add 2 tsp (10 ml) dish soap to the water.
Stir in a ¼-tsp salt and mix until the salt dissolves. This is the extraction mixture.
Place one strawberry into a plastic zipper-lock bag.
Pour the extraction mixture into the bag with the strawberry.
Remove as much air from the bag as possible and seal it closed.
Use your hands and fingers to mash, smash, and moosh the strawberry inside of the bag. You don’t want any large pieces remaining.
Pour the resulting strawberry pulp and extraction mixture through a strainer and into a medium glass bowl or similar container.
Use a spoon to press the mashed bits of strawberry against the strainer forcing even more of the mixture into the container. From the container it’s in now, pour the extraction mixture into a smaller glass container that holds ¼- to ½-cup (50-100 ml) of fluid. This will help to isolate the DNA on the surface of the mixture.
Add 1 tsp (5 ml) of the chilled isopropyl alcohol to the solution and hold the mixture at eye level. You’re looking for a separation of material that shows up as a white layer on top. That’s the DNA of the strawberry!
Use the tweezers to gently remove the DNA from the solution and lay it on a dish to examine.
How Does It Work
Whoa! The long thick fibers you pull out of the extraction mixture are real strands of strawberry DNA. As you may know, DNA is present in every cell of all plants and animals and determines all genetic traits of the individual organism.
While other fruits are soft and just as easy to pulverize, strawberries are the perfect choice for a DNA extraction lab for two very good reasons: (1) they yield way more DNA than other fruits, and (2) they are octoploid, meaning that they have eight copies of each type of DNA chromosome. (Human cells are generally diploid, meaning two sets of chromosomes.) These special circumstances make strawberry DNA both easy to extract and to see.
To extract the DNA, each component of the extraction mixture plays a part. Soap helps to dissolve cell membranes. Salt is added to release the DNA strands by breaking up protein chains that hold nucleic acids together. Finally, DNA is not soluble in isopropyl alcohol, especially when the alcohol is ice cold.