Experiment Title: Extracting DNA from Strawberries
Objective: To extract and observe visible DNA from strawberry cells using simple
household materials. Students will apply the scientific method and understand how
DNA can be isolated from cells.
Scientific Principle
Strawberries contain DNA in every cell. DNA is protected inside the nucleus, which is
surrounded by membranes. We use physical smashing and a chemical extraction
solution (soap and salt) to break cell membranes and release DNA. Cold alcohol is
used to make the DNA visible by causing it to precipitate (clump together).
Materials :
-1 ripe strawberry
-Resealable plastic bag
-2 teaspoons dish soap
-1 teaspoon salt
-½ cup water
-Measuring spoons
-Filter paper
-Funnel or strainer
-Clear cup or beaker
chilled
-Toothpick or wooden stick
-Cold rubbing alcohol (isopropyl),
-Small bowl
Procedure:
1. Remove the green top and place the strawberry into the resealable bag.
2. Mash the strawberry thoroughly for about 2 minutes.
3. Prepare the extraction solution by mixing:
o
½ cup water
o
2 tsp dish soap
o
1 tsp salt
4. Add 2 tablespoons of the solution to the mashed strawberry in the bag. Gently
mix for 1 minute.
5. Filter the mixture using a filter paper into a clear cup.
6. Slowly pour cold alcohol into the cup (equal volume to filtered liquid). Do not
mix.
7. Watch as white, stringy strands (DNA) appear at the top layer.
8. Use a stick or toothpick to spool (lift) the DNA.
Analysis Questions
1. Why is dish soap used in the DNA extraction process?
2. What role does salt play in the extraction?
3. Why is cold alcohol used, and why should it be poured slowly?
4. What would happen if you skipped the filtering step?