Sixth graders conducted a strawberry DNA extraction! They created a solution to break apart the cell membrane of a strawberry and separate the DNA from the nucleus. Strawberries are a good source of DNA because they have 8 copies of each type of chromosome. Students used an extraction buffer containing salt to break up protein chains that bind around the nucleic acids, and dishwashing detergent to dissolve the lipid or fat part of the strawberry cell wall and nuclear membrane. Lastly, they placed the DNA on a slide and examined it under a microscope.
Question to Explore
How can we extract the DNA from a strawberry and observe its structure under a microscope?
- 1 Ziploc freezer bag
- 1 strawberry
- 1 coffee filter or strainer
- 1 funnel
- 50 mL test tube
- 10 mL DNA extraction buffer
- 20 mL ice cold isopropyl alcohol
- 1 wooden skewer or tweezers
- Place the isopropyl alcohol in the freeze for two hours before conducting experiment.
- Prepare DNA extraction buffer. Add 900 mL water, then 50 mL dishwashing detergent, and 2 teaspoons salt into a container. Mix.
- Place one strawberry in a Ziploc bag.
- Smash/grind up the strawberry using your fist and fingers for 2 minutes.
- Add 10 mL of extraction buffer (salt and soap solution) to the bag.
- Kneed/mush the strawberry in the bag again for 1 minute.
5. Place your funnel above the test tube and hold your strainer above the funnel to create a filter.
6. Pour the strawberry slurry into the filter and let it drip directly into your test tube.
7. Slowly pour 20 mL cold isopropyl alcohol into the test tube. Very gently swirl the test tube once or twice.
8. Notice where the alcohol and extract layers come in contact with each other. Keep the test tube at eye level so you can see what is happening. What do you see appearing?
9. Dip the wooden skewer into the test tube where the strawberry extract and alcohol layers come into contact with each other. Pull out the skewer and transfer the DNA to a square of waxed paper. The fibers are millions of DNA strands!
10. Take a small sample of the DNA and prepare a slide. Stretch out the sample so that it is easier to view. View the DNA under the microscope. Sketch what you observe. How does what you view under the microscope differ from what you viewed with your naked eye?