BERRY FULL OF DNA
Overview:
Have you ever wondered what DNA really looks like? There are some organisms, like
strawberries, that have DNA so big you can see it without a microscope! In this
experiment you will extract the DNA from a real strawberry and even be able to see it
when you finish. You will never be able to eat a strawberry again without thinking of how
much DNA is in it!
Materials (per student group):
1. heavy duty zip lock baggie
2. 1 strawberry (fresh or frozen)
3. 10 ml DNA extraction buffer (soapy, salty water)
4. Filtering Apparatus: cheesecloth, funnel and small beaker
5. Ice cold ethanol
6. clear test tube
7. Glass rod, wooden skewer, or inoculating loop
Procedures:
1. Prepare an 8% soapy water solution by combining 250 mL H2O with 20 mL of dishwashing
detergent (not antibacterial) in a 750 mL beaker.
2. Prepare a 2% salt-water solution by combining 250 mL H2O with 1/8 teaspoon of salt in a 500 mL
beaker.
3. Transfer the 2% salt-water solution to the 750 mL beaker and mix the two solutions together. The
soapy salt-water solution will function as the DNA extraction buffer.
4. Place 1 strawberry in a ziplock plastic freezer storage bag.
5. Remove the air from the bag, seal it, and thoroughly mash the contents in the bag with your hands.
6. Pipette 10 mL of the DNA extraction buffer into the ziplock plastic freezer storage bag.
7. Remove the air from the bag, seal it, and mix the mashed strawberries and DNA extraction buffer
together.
8. Pour the strawberry mixture into the cheesecloth.
9. Twist each end of the cheesecloth and filter the mixture into the test tube. Use a funnel to facilitate
the transfer from the cheesecloth to the test tube. Fill ¼ of the test tube (10-15 mL) with the
strawberry mixture.
10. Remove the funnel from the test tube, and discard the cheesecloth with the leftover strawberry
mixture.
11. Use a pipette to drizzle 10 mL of ethanol down the insides of the test tube. The alcohol should
form a layer on top of the strawberry mixture. A white, stringy precipitate containing DNA should
begin to form.
12. Place the blunt end of a wooden skewer into the center of the test tube. Slowly rotate (not stir) the
skewer in one direction. The DNA should spool onto the wooden skewer.
Lab Questions
1. What did the DNA look like? Relate its chemical structure to how it looks when lots of it is
clumped together.
2. DNA is soluble in water, but not in ethanol. What does this fact have to do with our method of
extraction? Explain what happened when the ethanol came in contact with the strawberry extract.
3. A person cannot see a single cotton thread 100 feet away, but if you wound thousands of threads
together into a rope, it would be visible at some distance. How is this statement an analogy to our
DNA extraction?
4. In order to study our genes, scientists must first extract the DNA from human tissue. Would you
expect the method of DNA extraction to be the same for Human DNA? Why or why not?
5. Would the DNA be the same in any cell in the human body?
6. If you wanted to extract DNA from a living person, what cells would you use and why?
7. List two reasons why a scientist might want to study the DNA of strawberries.