Strawberry DNA

Concept: Deoxyribonucleic Acid (DNA)
Deoxyribonucleic acid (DNA) is the self-replicating material present in nearly all living organisms as the main constituent of chromosomes. It determines the genetics of individual organisms.

Read Aloud: Projects in Genetics by Claire O'Neal

Ingredients:

      ·         3 Strawberries
      ·         ⅓ cup Water
      ·         ½ tsp. Salt

      ·         1 tbl. Dish Soap

      ·         ½ cup Isopropyl Alcohol
      ·         Ziploc Baggies
      ·         Plastic Cups

      ·         Sieves

 Demonstration:

      ·         Put a bottle of isopropyl alcohol in the freezer.

      ·         Mix together ⅓ cup of water, ½ teaspoon of salt, and 1 tablespoon of dish soap in a plastic cup. Stir the solution thoroughly.

      ·         Place three strawberries in a Ziploc baggie. Use your hands to mash the strawberries inside of the baggie until there are no large pieces left.

      ·         Pour three tablespoons of the solution into the baggie. Remove as much air from the baggie as possible and seal it. Squeeze the strawberries with your fingers for one more minute.

      ·         Pour the resulting strawberry solution through a sieve and into a new plastic cup. Use a spoon to press the strained bits of strawberry against the sieve and force out more of the solution.

      ·         Slowly pour ½ cup of chilled isopropyl alochol down the side of the cup into the solution until there is a one-inch layer of alcohol on top of the solution.

      ·         Gently remove the thick white substance from the top of the solution using tweezers.

Experiment:

·         What happens if you use a fruit other than strawberries?

·         What happens if the isopropyl alcohol is room temperature?

Observations:
The long thick fibers on top of the solution are strands of DNA. Strawberry DNA is especially easy to extract because strawberries yield more DNA than any other fruits and they are octoploid, meaning they have eight copies of each type of DNA chromosome. When extracting DNA, each component of the extraction solution plays a part. The dish soap helps to dissolve the cell membranes. The salt is added to break up protein chains that hold nucleic acids together, releasing the DNA strands. Finally, DNA is not soluble in isopropyl alcohol, and even less so when the alcohol is cold.