DNA Extraction
Background
In this activity, you’re going to extract DNA from strawberries using diluted dish soap and alcohol. Suddenly
this mysterious secret of life can be seen materializing out of strawberry juice right in front of your eyes. The
long tangled DNA strands that ultimately form may be kept and collected using a glass stirring rod.
The DNA molecule is an invisibly thin, very long strand. The DNA found in each human cell is almost 2 meters
long. If all the DNA in a human adult (that’s 100 trillion cells) were laid end to end, the DNA would stretch 113
billion miles. That would take you to the sun and back 610 times. Even though DNA is invisible to the naked
eye, no microscopes are needed! The reason is that you release so many DNA strands that they tangle together
into a thick cable, visible without magnification. For example, it would be the same as if you took a thin piece
of thread and held it up on the far end of the hallway. You probably wouldn’t be able to see the thread from that
distance. However, if you took the thread and tangled it up with a hundred thousand other threads, you would
absolutely be able the tangled mess from quite a distance.
Purpose
Extract DNA.
Recognize that DNA is found in all cells.
Explain the steps needed to isolate DNA from a cell.
Describe the structure of DNA
Materials
Each team of 2 needs:
 1 fresh strawberry
 1 ziplock bag
 1 eppendorf tube
 1 clear glass test tube
 1 coffee filter
 1 funnel
 10 ml extraction buffer
 1 glass stirring rod
 Ethanol (3 mL)
 1 plastic pipette
 1 beaker
Procedure
1. Put the strawberry in the ziplock bag, squeeze out most of the air and seal the bag. The strawberry can
then be crushed into juice and pulp. Try to squish all of the chunks into an even, smooth puree. DO not
to pound the strawberry on the table or risk the bag bursting and getting strawberry pulp everywhere.
That won’t be fun for you to clean.
2. Next, open the bag and add 10 ml of extraction buffer. Seal the bag again and gently mix the strawberry
juice with the extraction buffer. Do not to mix too vigorously or it will generate a lot of bubbles and
can’t be filtered effectively. Use a gentle tilting back and forth motion while lightly squeezing the bag.
3. Set up a filtration system using a funnel and coffee filter.
4. Carefully pour the extract into your filtration system. Allow the juice to filter through into the container
below. Let it drip for 3-5 minutes.
5. Carefully transfer liquid from your beaker into the clear test tube until the test tube is about a third full.
6. Slowly add 3 ml of ice-cold alcohol to the test tube. The alcohol should be added so that it trickles down
the side of the tube before pooling on top of the strawberry extract. You should end up with a red bottom
layer and a clear top layer.
7. Make observations of anything going on in the clear alcohol layer.
8. After 2-3 minutes, a stirring rod can be inserted into the tube and gently swirled around. This will spool
the DNA around the stick. The DNA can be pulled out of the tube and stored in a microcentrifuge tube
filled with some alcohol. DO NOT STIR.
Discussion and Analysis Questions
1) Why is it necessary to mash the strawberries?
2) Why do you think we need to add the extraction buffer?
3) Do you think human DNA would look the same as strawberry DNA? Explain. (DO NOT just say “Yeah” or
“Nope”)
4) Why is the coffee filter used? How is the DNA able to get through the filter?
5) Can you see a single strand of DNA without a microscope? Explain how you were able to see the DNA in
this experiment without magnification.