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For the Love of Science: UVA Chemistry Students Engage Children with Strawberry DNA

Did you know that all living cells contain DNA? That’s right, every cell in your body, animals, and plants contains DNA. DNA is short for deoxyribonucleic acid, known as the “molecule of life.” This molecule contains instructions on how to make a living thing; DNA tells you to be you and a strawberry to be a strawberry. Normally, you cannot see DNA with the naked eye. However, if you collect it from thousands of cells, there is enough to be visible. In just a few simple steps, you can perform a DNA extraction at home using household materials! 

This “fun to do at home” science experiment is being brought to you by graduate and undergraduate student members of the Chemistry LEAD (Learning through Experiments and Demonstrations) Program at the University of VirginiaChemistry LEAD brings hands-on science experiments into Charlottesville-area elementary classrooms and provides activities at community events throughout the year to motivate and excite young learners about science. During 2012-2013, LEAD has reached 700 students through 15 school visits and an additional 1400 students through community events. LEAD aims to make science learning experiential and provide that spark that gets children interested in the world around them.

Strawberry DNA extraction is a great experiment to introduce children to the scientific method. Children can hypothesize what the DNA will look like. They can make predictions and record observations. Through the experiment, children get to do what scientists do – measure, observe, and predict. A very similar process is used to extract DNA in a real, high-tech laboratory! 

Isolating DNA allows scientists to study the molecule. For example, scientists could test DNA for genetic diseases or analyze it as forensic evidence. This experiment is also a great introduction to DNA, and could lead to an in-depth discussion on the structure and function of DNA in cells. 

Here’s what you will need to do a Strawberry DNA extraction:
Dish detergent
Water
Salt
Strawberries
Plastic baggie
Beaker or cup
Small cup or test tube
Coffee filter or cheesecloth
Measuring cup and spoons
Isopropyl alcohol (rubbing alcohol)

Here’s what you do:
First, prepare the extraction solution by mixing 2 tablespoons (30 mL) of water, ½ teaspoon dish detergent (2.5 mL), and 1/8 teaspoon of salt. Stir until dissolved. This will prepare enough solution for one strawberry DNA extraction. Scale up as needed.

Next, place a whole strawberry (or two if it is small, no need to remove the tops) into a zip lock bag. Add the extraction solution and seal. Carefully mash the strawberry for a few minutes or until there are no more big chunks.

Use a coffee filter, cheesecloth, or strainer to filter the solution into a cup. Transfer the filtrate (the solution you collected in the cup) to a small cup, beaker, or test tube. Add 2 teaspoons (10 mL) of cold isopropyl alcohol (rubbing alcohol). You should see two layers form. The DNA should begin to clump together and float to the top of the alcohol (top) layer. The DNA can be removed with tweezers or a toothpick. Use your scientific observation skills and record a description of the DNA! What does it look like? What color is it? What else do you notice?

Now, you might be curious about what each chemical does in the extraction:

  • The soap breaks open the cells, allowing the DNA inside to escape. 
  • Adding salt helps the DNA clump together. DNA is negatively charged, and will not want to be close to another DNA molecule (Remember that like charges repel and opposite charges attract - try this with magnets!). The positively charged sodium ions of the salt pair up with the negatively charged phosphates on DNA, making it neutral. The salt also keeps other proteins from being separated.
  • In the final step, the alcohol causes the DNA to precipitate (come out of solution) because DNA is insoluble, or unable to be dissolved in isopropyl alcohol. 

Why not compare strawberry DNA to DNA from other fruits and vegetables?
Bananas, kiwi, tomatoes, onion, and others can be used in place of strawberries in this experiment. How is their DNA similar or different?

Elementary School Teachers, Boy Scout and Girl Scout Leaders, if you are interested in having Chemistry LEAD at UVA bring hands-on science experiments into your school please contact us. We would love to share our passion for science with your students.  

Article by Joseph Houck,  5th year Ph.D. student at UVA, President of Chemistry LEAD

Photos by Susan Parmar at Virginia Discovery Museum’s Kid*Vention, February 2013

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