Name_________________________________________________
DNA Extraction Lab
We will be extracting DNA from strawberries using a
solution that contains water, detergent (to break down cell
membranes and other fats), salt and enzymes (to break down
proteins and carbohydrates). When the strawberry is smushed,
these components go to work and help chemically break down
cellular materials surrounding the DNA. This strawberry and DNA
extraction solution will be strained to remove all solid material, and
then alcohol will be added to the remaining strawberry liquid. The
alcohol must be ice-cold, as the cold temperature protects the
strawberry DNA from enzymes in the strawberry cells called DNases,
which destroy DNA if it enters the cytoplasm of a cell (this helps
protect cells from viruses!). Adding alcohol will cause the DNA to be
removed from the water-based extraction solution, because alcohol is charged, and DNA will
bond to it. Alcohol is less dense than water, so if the experiment is successful, DNA should be
found floating in the alcohol layer above the water!
Materials:
Plastic bag
Strawberry
Small graduated cylinder
DNA Extraction Solution (10 mL)
Piece of cheesecloth
Funnel
Test tube
Small beaker
Alcohol (30 mL)
Glass rod
Procedure:
1. Remove green leaves from the top of the strawberry. Discard leaves in the trash.
2. Open the plastic bag and place the strawberry inside.
3. Obtain 10 mL of the DNA Extraction Solution.
4. Smush the strawberry with the Extraction Solution for about 2 minutes. Make sure the
strawberry is as liquefied as possible. Be careful not to poke a hole in the bag!
5. Open the bag and pour the liquefied strawberry + Extraction Solution into the funnel
lined with cheesecloth. Wait 2 minutes for the solution to strain and drain.
6. Remove the funnel and cheesecloth. Discard the cheesecloth. Rinse the funnel and put it
aside to dry.
7. Obtain 30 mL of alcohol. The alcohol will be in an ice bath to keep it cold. PUT
IT BACK IN THE ICE BATH WHEN YOU ARE DONE!
8. Carefully and slowly pour 30 mL of alcohol into the strawberry solution. Wait 2
minutes for the DNA to bond to the alcohol.
9. Two layers of liquid should have formed: a pink layer on the bottom and a clear
layer on top, with white strands floating in the clear top layer.
10. The white strands are DNA! Use the glass rod to attempt to remove them, and
note your observations about the substance you obtained.
Observations about DNA:
Questions:
1. For the DNA extraction solution, why was detergent needed? How about the salt and
enzymes? How about the alcohol? Would this experiment have worked without any of
these elements? Explain.
2. Why does the alcohol have to be as cold as possible?
3. What did the DNA you obtained look like? Were you surprised at its appearance, or at
the amount you obtained?
4. List two possible scientific questions that could be explored by studying strawberry
DNA.
Instructor Notes:
To make detergent solution:
1 cup cold water
1/8 teaspoon salt
1/8 teaspoon meat tenderizer
2 tablespoons detergent (clear if possible)