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Transcript
Name: ___________________________________________________________________ Date: ___________________________________ Period: ____________
Strawberry DNA Extraction Lab
Overview:
This DNA extraction results in beautiful, white, spoolable DNA. You will never be able to eat a strawberry again without
thinking of how much DNA is in it!
Objectives:
Students will be able to:
1) Explain how DNA is found in all the food we eat by extracting DNA from strawberries.
2) Describe the connection between DNA and cells – every living and once living things have cells, therefore, DNA.
3) Extract DNA from plant cells (strawberries).
Background: DNA is found in cells from Animals and Plants. DNA is a double stranded macromolecule composed of
nucleotide bases pairing Adenine with Thymine and Guanine with Cytosine. DNA can be extracted from cells by a simple
technique with household chemicals, enabling students to see strands of DNA with the naked eye.
One of the reasons strawberries work so well is that they are soft and easy to pulverize. Also, ripe strawberries are producing
pectinases and cellulases which are already breaking down the cell walls. We also physically break apart the cell walls by
crushing the strawberries. Most interestingly, strawberries have enormous genomes. They are octoploid, which means they
have eight of each type of chromosome. The detergent in the shampoo helps to dissolve the phosholipid bilayers of the cell
membrane and disrupts the nuclear membranes of each cell to release the DNA. The salt neutralizes the negative charges on
the DNA and thus enables the DNA strands to stick together. It also causes proteins and carbohydrates to precipitate. DNA is
not soluble in ethanol. When molecules are soluble, they are dispersed in the solution and are therefore not visible. When
molecules are insoluble, they clump together and become visible. The colder the ethanol, the less soluble the DNA will be in it.
This is why it is important for the ethanol to be kept in the freezer or in an ice bath.
Pre – Lab Questions
1. How do you think DNA looks like in the naked eye?
2. What is DNA’s function?
3. Where in the cell is DNA located?
4. Have you ever eaten DNA? Explain.
5. In order to remove DNA from a cell, what parts of a cell must we break through?
6. Why do we “crush” the strawberry?
7. Why do we use shampoo?
8. What does the salt do?
9. What does the cold ethanol do?
10. Do you think all organisms have the same amount of DNA? Why or why not?
Expected Results:
When the students layer the ethanol on their strawberry extract, they will start to see the fine white strands of DNA form at
the interface. When they stir the DNA into the ethanol layer, the DNA will form cotton candy like fibers that will spool onto the
stirring rod.
Materials (per student group):
1. Strawberry soup
2. 2 ml DNA extraction buffer
(soapy, salty water)
3. graduated cylinder and droppers
4. 40 ml Ice cold ethanol
5. Clear test tube
6. Stirring rod
7. Wooden Stirrer
Procedure:
1.
2.
3.
4.
5.
6.
DONE ALREADY BY TEACHER: Blend the strawberries to make a mushy strawberry soup.
Place 5 mL of strawberry soup (mush) into a test tube.
Add 2 ml (1 full pipette) extraction buffer (blue soapy) to the test tube
Stir the test tube with a stirring rod.
Support the test tube so it doesn’t tip over.
SLOWLY pour 10 ml of ice-cold alcohol into the tube until the tube is half full and forms a layer over
the top of the strawberry extract.
7. At the interface, you will see the DNA precipitate out of solution and float to the top. You may spool
the DNA on your glass rod or wooden stirrer.
8. Spool the DNA by dipping a wooden stirrer or glass rod into the tube right where the extract layer &
alcohol are in contact with each other. With your tube at eye level, twirl the rod & watch as DNA
strands collect.
9. Wash all materials and put them where they need to go. Make sure all lab tables and stations are
clean!
Analysis Questions
Take a look at the sketch of the plant cell below. The chromosomes (which are made of DNA) are in the nucleus. This is the
only place where DNA is located.
1. Now match the procedure with what it is doing to help isolate the DNA from the other materials in the cell.
_____1. Break open the cell
A. Squish the fruit to a slush
_____2. Dissolve cell membranes
_____3. Precipitate the DNA (clump the DNA together)
_____4. Separate organelles, broken cell wall, and
membranes from proteins, carbohydrates, and DNA
B. Filter your extract through cheesecloth
C. Mix in a detergent solution
D. Layer cold alcohol over the extract
2. What did the DNA look like?
3. DNA is soluble in water, but not in ethanol. What does this fact have to do with our method of extraction?
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 at some distance. How is this statement an analogy to our DNA extraction?
5. Describe the connection between DNA, organelles, cells, and living things.
6. List 5 other organism’s DNA you eat on a weekly basis.
7. What would DNA code for in strawberries? (List 3 different things)
Extend
7. 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?
8. List two reasons why a scientist might want to study the DNA of strawberries.