Little experiment, big results: how to extract DNA from a strawberry

The recipe to extract DNA from a strawberry

Extracting strawberry DNA science

Each individual cell in an organism has a copy of the DNA pattern used to reproduce that cell. Usually, the DNA is combined within the cell, so we can’t see it. But when we create a mixture of dish soap and salt and mix it with the strawberry pulp, it helps break down the strawberry cells into individual parts.

Once the alcohol is added to the pulp, it encourages the DNA strands to rise to the top and bind together, where you can see them together in one long, clear strand. 

Let’s see the steps to extract DNA from strawberries.

The experiment

1. 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.
2. Add 2 tsp (10 ml) dish soap to the water.
3. Stir in a ¼- tsp salt and mix until the salt dissolves. This is the extraction mixture.
4. Place one strawberry into a plastic zipper-lock bag.
5. Pour the extraction mixture into the bag with the strawberry
6. Remove as much air from the bag as possible and seal it closed.
7. Use your hands and fingers to mash, smash, and moosh the strawberry inside of the bag. You don’t want any large pieces remaining.
8. Pour the resulting strawberry pulp and extraction mixture through a strainer and into a medium glass bowl or similar container.
9. 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.
10. 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!
11. Use the tweezers to gently remove the DNA from the solution and lay it on a dish to examine.

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: they yield way more DNA than other fruits; they are octoploid, meaning that they have eight copies of each type of DNA chromosome. 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.

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