Museum of Science and Industry

Extract DNA

There are many similarities between plants and animals. Inside every plant and animal cell is a nucleus containing DNA. But to study DNA, you first need to remove DNA from cells.

What You'll Need

Water
Salt
Shampoo or dish soap (clear shampoo with EDTA, such as Suave Daily Clarifying, works best)
Cold 70% to 95% isopropyl alcohol (place in freezer overnight)
Ziploc-type bag
Strawberries or other foods like grapes, kiwi, tomatoes, bananas or lettuce
Test tube
Coffee filter
Plastic cup
Pipette

What to Do

Create the DNA extraction buffer by mixing 450 milliliters of water with two teaspoons of salt. Gently add 50 milliliters of shampoo (this recipe is enough for 50 groups of students).

Place a strawberry in a Ziploc bag and gently mash for two minutes, being careful not to pop the bag. Use a pipette to add 10 milliliters of the DNA extraction buffer to the bag and mash for one minute.

Assemble the DNA filter by draping a coffee filter over a plastic cup. Make sure the bottom of the filter does not touch the bottom of the cup, and the top of the filter is folded over the cup to hold it in place. Pour the strawberry mixture into the coffee filter and let it drain for five to 10 minutes.

Pour a small amount (three to four milliliters) of the filtered strawberry solution into a test tube. Tilt the tube and pour an equal amount of cold isopropyl alcohol into the test tube. The DNA will precipitate to the top of the solution and will resemble a white, fluffly cloud.

What's Happening

The shampoo helps dissolve the fatty cell membrane, while the salt makes the DNA molecules stick together and breaks up the proteins that bind to the DNA. The alcohol causes the DNA to precipitate, or rise to the top of the solution.