Name: __________________________
Period: __________
Date: ___________________
LAB EXERCISE
DNA EXTRACTION
Introduction: Whoa! Did you know that DNA is in the food you eat? In fact each
macromolecule (carbs, lipids, proteins, and nucleic acids) can be found in every fruit,
vegetable, and piece of meat you digest. This is because these organisms are made up of
cells and we all know what cells are made of, right?
What are all cells made of? ____________________________________________________
Between 40-70 billion (billion with a b!) of your cells die every single day. Your body must
replace these cells at the rate that they die out and it accomplishes this through mitosis. As
you’ve learned, mitosis is a process of cell duplication and division that begins with one cell
and ends with two. This is how your body grows and how you replace dead cells.
Before a cell divides, it has to duplicate its DNA so that each of the two new cells gets a copy.
But in order to build more DNA, the body must have a source for the building blocks of DNA.
What are the building blocks of DNA? ___________________________________________
Where does your body get these building blocks from? ______________________________
Today, we will extract (remove) the DNA of a well-known organism. In this experiment, you will
isolate the DNA of a strawberry (scientific name: Fragaria ananassaI) using simple household
items and then observe the resulting material using a microscope.
Based on what you learned about the function of DNA, explain why strawberry cells need
DNA: ______________________________________________________________________
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Problem statement: Can the DNA of Fragaria ananassa be extracted using alcohol, salt, and
dish soap?
Materials:
1 strawberry
Materials:
measuring utensils & scale
5 mL isopropyl alcohol
2 beakers
10 mL dish soap
1 set of tweezers
1/4 teaspoon salt
1 pipette
1 ziploc bag
1 spoon
1 sieve
1 blank microscope slide
90 mL water
1 microscope
Procedures:
1. Place a bottle of isopropyl alcohol in a freezer.
2. Measure the mass of one strawberry (in grams).
3. Measure 90 mL of water into a beaker or similar container.
4. Pour 10 mL of dish soap into the 90 mL of water.
5. Add 1/4 tsp of salt to the liquid in the beaker.
6. Mix it all up and now you've got a homemade extraction solution!
7. Place one strawberry in a plastic zipper-lock bag.
8. Pour your extraction solution into the bag with the strawberry.
9. Remove as much air from the bag as possible and seal it.
10. Use your hands to mash, smash, and mush the strawberry inside of the bag until there are
no large pieces remaining.
11. Pour the resulting strawberry/extraction solution mixture through a sieve and into a beaker
or similar container.
12. Use a spoon to press the strained bits of strawberry against the sieve, forcing even more
of the solution into the beaker.
13. From the container it is currently in, transfer the solution into a smaller beaker or similar
container that holds around 50-100 mL of fluid.
14. Add 5 mL of your chilled isopropyl alcohol to the solution and hold the mixture at eye level.
15. Can you see how there is a separation of white “stuff” atop the rest of the solution? That's
the DNA of the strawberry.
16. Gently remove the DNA from the solution using tweezers.
17. Measure the mass of the DNA extraction using a scale.
Data:
mass of strawberry: ____________________
mass of DNA: ____________________
What percent of a strawberry’s mass is DNA? __________________________________
Write your observations here (qualitative data). Is what you observed consistent with what you
know about the structure of DNA? _____________________________________
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Data Analysis:
While other fruits are soft and just as easy to mince, strawberries are the perfect choice for a
DNA extraction lab for two reasons: they yield more DNA than any other fruits, and they are
octoploid, meaning that they have eight copies of each type of DNA chromosome. These
special circumstances make strawberry DNA easy to extract and see. (Human cells are
generally diploid, with only two sets of chromosomes.)
To extract the DNA, each component of the extraction solution plays a part. The soap helps to
dissolve the cell membranes. The salt is added to break up protein chains that hold nucleic
acids together, releasing the DNA strands. Finally, DNA is not soluble in isopropyl alcohol, and
even less so when the alcohol is ice cold.
Conclusion: Why is it relatively simple to extract the DNA of Fragaria ananassa?
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