Name ____________________________________________________
Date _______________
Activity: DNA Extraction
Goals:
1. To extract a small amount of DNA from cells.
2. To observe the DNA molecule removed from once living cells.
Background Information: DNA is the largest molecule known. A single, unbroken
strand of it may contain many millions of atoms. In fact, all 46 human chromosomes
contain an estimated three billion base pairs in the DNA molecules. When scientists
want to work with DNA, they first need to extract or remove the DNA from inside a cell.
All living cells have DNA found within the nucleus of the cell. In this activity there will be
three steps needed to remove the DNA from a cell. The first step is lysis which splits the
cell open so we can get the DNA out. We do this by crushing the strawberry and
dissolving the cell wall with a detergent and salt solution. The second step is
deproteinization which dissolves the layer of protein that covers the DNA. The final step
is extraction which is when alcohol is used to separate the DNA from the rest of the cell
material.
Materials: The following materials are for one pair of students: one sandwich size
ziplock bag, 1 strawberry, ~15ml DNA lysis liquid (detergent and salt solution) in a small
beaker, cheese cloth cut in a 5 inch square, large clear plastic tumbler, 10 ml ice cold
isopropyl alcohol in a tiny shot glass (plastic cup), a test tube, stirring rods or coffee
stirrers
Procedure:
1. What I Know: Write a sentence or two describing what you think the DNA will look
like.
2. Work with a partner. You will need 1 strawberry. Pull off any green leaves off the
strawberry.
3. Place the strawberry into the Ziploc bag, remove the air from the bag and crush it
in the bag for about 2 minutes.
4. Add ~15 ml of the DNA lysis liquid into the bag.
5. Crush the contents for another minute; avoid making too many bubbles.
6. Place a square of cheesecloth over an empty small plastic cup allowing the cloth to
slightly dip into the cup.
6. Cut the corner of the Ziploc bag and slowly pour the contents through the cheese
cloth and into the plastic cup. Be sure that one partner holds the cheesecloth in place
during the pouring procedure. Wait until there is about 1 inch of liquid in the cup.
7. Pour the strained strawberry liquid into a clean test tube until the test tube is about
half-way filled.
8. Slowly pour cold alcohol into the test tube until the test tube is about ¾ full. Do not
mix the layers. Leave the test tube undisturbed for at least 2 minutes.
9. Watch for the development of a white cloudy material (DNA) where the alcohol meets
the liquid.
10. You can gently wind the DNA on a stirring rod or onto a coffee stirrer.
11. What I Did: Write a short summary of the procedure you used for this activity.
12. What I Observed: Make a drawing of the test tube before and after the addition of
the alcohol.
Before alcohol is added to test tube
After alcohol is added to test tube
13. What I Learned: Write a detailed summary of what you learned from completing this
activity.
14. What I Wonder: Pose a why or how question that you may still have about DNA
and replication.
15. Questions:
a. Describe how the DNA appeared. How was the DNA different from what you
expected?
b. Create a 3-Box cartoon strip describing the importance of DNA in your life.
Caption:
Caption:
Caption:
DNA Lysis Liquid:
You will need ~ 1000ml of this solution for all 4 classes.
In a 1000ml beaker add 100ml of clear liquid detergent, 2 heaping teaspoons of salt
without iodine, and enough tap water to make a 1000 solution.