Abstract

Objective

In this experiment, you will design a DNA Extraction Kit and use it to purify DNA from strawberries.

Introduction

All living things come with a set of instructions stored in their DNA, short for deoxyribonucleic acid. Whether you are a human, rat, tomato, or bacteria, each cell will have DNA inside of it. DNA is the blueprint for everything that happens inside the cell of an organism, and each cell has an entire copy of the same set of instructions. The entire set of instructions is called the genome.

Scientists study DNA for many reasons. They can figure out how the instructions stored in DNA help your body to function properly. They can use DNA to make new medicines. They can genetically modify foods to be resistant to insects. They can figure out the suspect of a crime. They can even use ancient DNA to reconstruct evolutionary histories!

How do scientists get the DNA out of a cell so that they can study it? This is called a DNA extraction, and there are many DNA extraction kits available from biotechnology companies for scientists to use in the lab. During a DNA extraction, a detergent will cause the cell to pop open, or lyse, so that the DNA is released into solution. Then the DNA can be precipitated out of the solution by adding alcohol. In this experiment you will make your own DNA extraction kit from household materials and use it to purify DNA from strawberries.

Strawberries are octoploid, which means they have eight copies of the DNA in their genome in every cell!

Why use strawberries to test your DNA extraction kit? Because strawberry cells each have eight copies of the genome in every cell! When an organism has eight copies, called an octoploid, it has a lot more DNA per cell than an organism that only has one copy. Using DNA from strawberries will help you have a successful DNA preparation so you can purify a lot of DNA.

Terms, Concepts, and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more!

• DNA
• Genome
• Extraction
• Lyse
• Precipitate
• Octoploid

• How can you extract the DNA out of a strawberry?
• What does each ingredient do? (detergent, salt, alcohol)
• Will I be able to see the DNA without using a microscope?

Bibliography

• This project is from the "Understanding Genetics: Human Health and the Genome" exhibit at The Tech Museum of Innovation in San Jose, CA:
  The Tech, 2004. "Making Medicine: Do-It-Yourself Strawberry DNA," The Tech Museum of Innovation, San Jose, CA. [accessed March 6, 2007] http://www.thetech.org/genetics/medicine.php
• Another similar project can be found from the Santa Clara College Biotechnology Education Program (SCCBEP) at San Jose State University:
  SCCBEP, 2002. "DNA Spooling from Strawberries," Santa Clara College Biotechnology Education Program (SCCBEP), San Jose State University, CA. [accessed March 6, 2007] http://www.science.sjsu.edu/sccbep/resources/curriculum/dna_spooling_strawberry.pdf
• Visit the online "Understanding Genetics: Human Health and the Genome" exhibit at the Tech Museum of Innovation and click on the "Zooming Into DNA" online exhibit. This is a great way to understand and visualize where the DNA in your body is:
  Rosa, C. et. al., 2007. "Zooming Into DNA," The Tech Museum of Innovation, San Jose, CA. [accessed March 6, 2007] http://www.thetech.org/genetics/index.php
• Want to try a DNA Extraction the way it is done in a real laboratory? Try the DNA Extraction Virtual Laboratory from the University of Utah:
  Univ. of Utah, 2006. "DNA Extraction Virtual Lab," The Genetic Science Learning Center, University of Utah, Salt Lake City, UT. [accessed March 6, 2007] http://learn.genetics.utah.edu/units/biotech/extraction/

Materials and Equipment

• Measuring cup
• Measuring spoons
• Rubbing alcohol
• 1/2 teaspoon salt
• 1/3 cup water
• 1 tablespoon dishwashing detergent (Dawn®)
• Glass or small bowl
• Cheesecloth
• Funnel
• Tall drinking glass
• 3 strawberries (green tops removed)
• Resealable plastic sandwich bags
• Test tube or small glass jar (e.g., spice jar)
• Bamboo skewer (find them at the grocery store)

Experimental Procedure

1. Chill the rubbing alcohol in the freezer. (You'll need it later.)
2. Mix the salt, water, and Dawn detergent in a glass or small bowl. Set the mixture aside. This is your extraction liquid.
3. Line the funnel with the cheesecloth, and put the funnel's tube into the glass.
4. Put the strawberries in the plastic bag and push out all the extra air. Seal it tightly.
5. With your fingers, squeeze and smash the strawberry mixture for 2 minutes.
6. Add 3 tablespoons of the extraction liquid you made in Step 2 to the strawberries in the bag. Push out all the extra air and reseal the bag. The liquid detergent will help break the strawberry cells open allowing the DNA to spill out. The salt helps create an environment where the different strands of DNA can gather together in a clump making it easier for you to see them.
7. Squeeze the strawberry mixture with your fingers for 1 minute.
8. Pour the strawberry mixture from the bag into the funnel. Let it drip into the glass until there is no liquid left in the funnel.
9. Throw away the cheesecloth and the strawberry pulp inside. Pour the contents of the glass into the test tube or small glass jar so it is 1/4 full.
10. Tilt the test tube or jar and very slowly pour the cold rubbing alcohol down the side. The alcohol should form a layer on top of the strawberry liquid. (Don't let the alcohol and strawberry liquid mix. The DNA collects between the two layers!) DNA does not dissolve in alcohol. When alcohol is added to the mixture, the rest of the mixture, except for the DNA, stays in solution, while the DNA precipitates out into the alcohol layer—that’s the gooey clear/white stuff you can collect with a skewer or other thin rod.
11. Dip the bamboo skewer into the test tube where the alcohol and strawberry layers meet. Pull up the skewer. The whitish, stringy stuff is DNA containing strawberry genes!

Variations

• You can try these steps to purify DNA from lots of other living things. Grab some oatmeal or kiwis from the kitchen and try it again! Which foods give you the most DNA?
• If you have access to a milligram scale (called a balance), you can measure how much DNA you get (called a yield). Just weigh your bamboo skewer using milligrams before and after the DNA purification. Then subtract the starting weight from the final weight to get your final yield in milligrams (mg).
• Compare your yield in milligrams (mg) under various experimental conditions:
  • Start with different amounts of strawberries— is more better?
  • Change some of the components of your kit— will other detergents work better?
  • Start with different materials— are there other sources of DNA with higher yields?

• For more science project ideas in this area of science, see Biotechnology Techniques Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Sources

• This project is from the "Understanding Genetics: Human Health and the Genome" exhibit at The Tech Museum of Innovation in San Jose, CA:
  The Tech, 2004. "Making Medicine: Do-It-Yourself Strawberry DNA," The Tech Museum of Innovation, San Jose, CA. [accessed March 6, 2007] http://www.thetech.org/genetics/medicine.php
• Another similar project can be found from the Santa Clara College Biotechnology Education Program (SCCBEP) at San Jose State University:
  SCCBEP, 2002. "DNA Spooling from Strawberries," Santa Clara College Biotechnology Education Program (SCCBEP), San Jose State University, CA. [accessed March 6, 2007] http://www.science.sjsu.edu/sccbep/resources/curriculum/dna_spooling_strawberry.pdf

Last edit date: 2011-03-03 11:00:00