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Hands-On Science

biology

Strawberry DNA

See how DNA is in all living things ... even strawberries!

Materials

  • 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

Directions

This recipe is enough for a group of 50 students.

  1. Create the DNA extraction buffer by mixing 450 milliliters of water with two teaspoons of salt.
  2. Gently add 50 milliliters of shampoo.
  3. Place a strawberry in a Ziploc bag and gently mash for two minutes, being careful not to pop the bag.
  4. Use a pipette to add 10 milliliters of the DNA extraction buffer to the bag and mash for one minute.
  5. 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.
  6. Pour the strawberry mixture into the coffee filter and let it drain for five to 10 minutes.
  7. Pour a small amount (three to four milliliters) of the filtered strawberry solution into a test tube.
  8. 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, fluffy 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.

Extensions

Try to extract DNA from other fruits and vegetables like grapes, kiwi, tomatoes, bananas or lettuce. Which fruit or vegetable produces the most DNA?

Try different types of shampoo and dish soap and compare the results.

Background information

Cells are the functional and structural unit for life in both plants and animals. There are pretty obvious differences between the two, but also many similarities. Both have many of the same organelles, including a nucleus, which is the control for the cell. The nucleus contains DNA, or deoxyribonucleic acid. In both plants and animals, the DNA is in the same shape - the famous double helix - that resembles a spiral staircase.

DNA molecules in plant cells and animal cells are made from the same four chemical building blocks: adenine, cytosine, guanine and thymine. The way the nucleotides are arranged and the information they encode determines whether the organism will grow fur, scales, leaves or skin.