DNA Extraction From a Strawberry
Objectives: SWBAT extract DNA from strawberries; observe what DNA looks
like to the naked eye; learn that DNA is found in every living and (once living)
thing.
Background and Review
How does it work?
Strawberries
This is the DNA source in this activity. Strawberries contain plenty of DNA in their cells, plus they have seeds
that also contain DNA. The seeds contain many nutrients as well. Actually, many other fruits work just as well
as strawberries for DNA extraction.
Detergent
Detergent contains sodium laurel sulfate, which cleans by removing fats and proteins. It acts the same way in
the DNA extraction activity, pulling apart the fats (lipids) and proteins that make up the membranes
surrounding the cell and nucleus. Once these membranes are broken apart, the DNA is released from the cell.
Soap molecules and grease molecules are made of two parts:
Heads, which like water
Tails, which are afraid of water
Both soap and grease molecules organize themselves in
bubbles (spheres) with heads outside to face the water
and tails inside to hide from the water. When soap comes
close to grease, it captures it, forming a greasy soapy ball.
A cell’s membranes have two layers of lipid (fat) molecules with proteins going through them.
When detergent comes close to the cell, it captures the lipids and proteins and releases the DNA.
Alcohol
The DNA released from the cell nucleus is dissolved in the salt/detergent/strawberry solution and cannot be
seen. DNA precipitates out of solution in alcohol, where it can be seen. Besides allowing us to see the DNA, the
alcohol separates the DNA from the other cell components, which are left behind in the water solution.
Name: _______________________________ Date: ____________ Block: ____________
Experiment:
Strawberry DNA Extraction
Materials:
Worksheets: Student pre-lab, DNA extraction lab, student response.
 1 Zip-type, freezer bag (6”x 9”)
 1 square of cheesecloth
 1 Plastic cup, 5 oz.
 1 Plastic pipette
 1 Strawberry 
 10 mLs DNA extraction buffer (soapy, salty water) 
 15 mLs ice cold ethanol in test tube
Procedure:
Working together in your lab groups, read through the entire procedure and
follow the steps in Parts I, II and III.
Part I- Preparing the DNA extract
1.
Have one person get the lab supplies while another person gets the
strawberry and removes the stem and leaves.
2.
Place one strawberry in a zipper bag.
3.
Gently mash up the strawberry for 2 minutes (thoroughly mash, but don’t pop the bag!).
4.
Add 10 mLs of the extraction buffer to the bag.
5.
Mash again for 1 minute. While one partner is mashing the other partner must do step 6.
6.
Drape the cheesecloth in the filter. Make sure the top part of the filter is folded over the top of your cup and
that the bottom of the filter does not touch the bottom of the cup.
7.
Pour the mashed strawberries with the extraction buffer into the filter and let drip into the bottom of the cup.
This takes a few minutes. As you wait for your solution to filter, complete the following questions:
Part I: Questions
1. What was the purpose of mashing up the strawberry?
2. What does the extraction buffer do? (Hint: Extraction buffer contains soap. What does soap do when you wash your
hands?)
3. What does the filter do?
Part II: Pipetting the strawberry extract into the alcohol
8. One person gets a test tube that contains ice cold ethanol (your teacher will pour it in).
9. Using a pipette, remove some of the strawberry extract from the cup. Carefully pipette
the strawberry extract into the alcohol in the test tube and watch the solution precipitate
(separate). DO NOT SHAKE THE TUBE!!! Very gently swirl the tube once or twice.
(Watch your teacher for a demo on how to do this!!) Then let the tube remain undisturbed.
Part III: Observations
10. Watch where the alcohol and extract layers come in contact with each other. Keep the
tube at eye level so you can see what is happening.
What do you see appearing?
(Sketch what you see in the box and note any other observations.) 
Questions Parts II and III:
1. What happens when you add the filtrate to the alcohol?
2. What does the DNA look like?
Sketch/Observations
Conclusions and Analysis
1. It is important that you understand the steps in the extraction procedure and why each step was necessary.
Each step in the procedure aided in isolating the DNA from other cellular materials. Match the procedure with
its function:
PROCEDURE
FUNCTION
A. Filter strawberry slurry through cheesecloth
____ To precipitate DNA from solution
B. Mush strawberry with salty/soapy solution
____ Break open the cells
C. Initial smashing and grinding of strawberry
____ Separate components of the cell
D. Addition of ethanol to filtered extract
____ Break up proteins and dissolve cell membranes
2. What did the DNA look like? Relate what you know about the chemical structure of DNA to what you
observed today.
3. Explain what happened in the final step when you added ethanol to your strawberry extract. (Hint: DNA is
soluble (dissolvable) in water, but not in ethanol)
4. 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 much further away. Does this statement relate to our DNA extraction? Explain.
5. Why is it important for scientists to be able to remove DNA from an organism? List two reasons.
6. Is there DNA in your food? ________ How do you know?