Biology DNA Extraction Lab Procedure/Data Sheets
The purpose of DNA extraction is to visually observe DNA from a living organism. Strawberries are an ideal fruit to use because they are readily available. They are also octoploid, which means they contain eight copies of each chromosome.
Materials:
1 strawberry
1 heavy duty zipper seal bag
2 teaspoons of water
1 teaspoon of soap (dishwashing detergent)
Salt
1 50mL beaker
1 funnel lined with cheesecloth
1 glass stirring rod or popsicle stick
1 syringe to dispense ethanol
20mL freezer cold ethanol
Procedure:
1. Place a strawberry into a zipper seal bag. Seal the bag, removing the air.
2. Begin to break down the strawberry by smashing it in the bag with fists and fingers for 2-3 minutes. Be careful to not break the bag.
3. Add two teaspoons of water to liquefy the strawberry pulp.
4. Add one teaspoon of soap. The soap acts to dissolve the phospholipid bilayer of the cellular membrane and of the cell’s organelles.
5. Add one pinch of salt to the bag. The salt acts to break up the protein chains around the nucleic acids, thus allowing for the DNA extraction.
6. Mix by kneading the mixture in the bag again for 1-2 minutes.
7. Assemble the filtration system. Line the funnel with paper towel and then place the funnel into the beaker (as shown).
8. Slowly pour the strawberry mixture out of the bag and into the filtration system, allowing the filtered liquid to collect in the bottom of the beaker.
9. Remove the funnel and cheesecloth.
10. While slowly stirring the strawberry mixture, slowly dispense the 20mL of ethanol down the inside wall of the beaker using the syringe. The ethanol must be freezer cold! DNA is not soluble in cold ethanol; thus, it comes out of solution and can be extracted.
11. Slowly stir to collect DNA (the slimy substance) on the end of the stirring rod.
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 ___ Separate components of the cell
C. Initial smashing and grinding of strawberry ___ Break open the cells
D. Addition of ethanol to filtered extract ___ Break up proteins and dissolve cellmembranes
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 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. Is this statement
analogous 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?
In order to study our genes, scientists must first extract the DNA from human tissue. Would you expect the method of DNA extraction to be the same for Human DNA? Why or why not?
7. Would the DNA be the same in any cell in the human body? Explain
8. If you wanted to extract DNA from a living person, what cells would you use and why?
9. List two reasons why a scientist might want to study the DNA of strawberries.