Name: ___________________________ Date: _____________ Period: 1 2 3 4 5 6 7
Strawberry DNA Extraction Lab
Introduction:
Have you ever wondered what DNA looks like? Today you are going to break apart the cell
membrane of a strawberry and separate the DNA from the nucleus. Strawberries are a good
source of DNA because they have 8 copies of each type of chromosome! Humans only have 2
copies of each chromosome. This large number of chromosomes will filter out of your solution
and you will get to actually see DNA!
Review:
QUESTION 1. Where in the cell is the DNA found?
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BACKGROUND: 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 place where most of the DNA is located. (There
are also small amounts of DNA in the chloroplast and mitochondria.)
QUESTION 2. What do you think the DNA will look like when you extract it from the plant
cell? (Write or draw a brief description.)
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Materials
1 Zip-type, freezer bag (6”x 9”)
1 Coffee filter, cone-shaped, #2 size
1 Plastic cup, 5 oz.
1 Plastic pipette
Available from your teacher:
1 Strawberry
10 mLs DNA extraction buffer (soapy, salty water)
15 mLs ice cold ethanol in test tube
1 rubber band
1 small beaker to stand the test tube up
1 plastic wand to spool DNA
1 empty test tube
Procedure
Working in groups of two, read through the entire procedure and follow the steps
in Parts I and II.
Part I- Preparing the DNA extract
________1. Have one partner get supplies while the other partner gets
one strawberry.
________2. Place one strawberry in a zipper bag and close it securely.
________3. Mash up the strawberry for 1 minute until is it is “soupy.”
________4. Add 10 mL of the extraction buffer to the bag.
________5. Mash again for 1 minute. While one partner is mashing
the other partner must do step 6.
________6. Drape the coffee filter in the cup. Make sure the top part
of the filter is folded over the top of your cup and that the bottom of
the filter does not touch the bottom of the cup.
_______7. Pour the mashed strawberries with the extraction buffer
out of the plastic bag into the filter.
_______8. Let the solution drip into the bottom of the cup. This
takes about 10 minutes.
As you wait for your solution to filter,
complete the following questions:
Part I: Questions
A. What was the purpose of mashing up the strawberry?
B. What does the extraction buffer do? (Hint: Extraction buffer contains soap. What does
soap do when you wash your hands?)
C. What does the filter do?
D. What do you see appearing? (Sketch what you see and note any other observations.)
PROCEDURES Part II: Pipetting the strawberry extract into the alcohol
______8. One partner gets a test tube that contains ice cold ethanol. Place this test tube in the
small beaker standing up.
______9. Carefully remove the rubber band. Remove the coffee filter and place it in the trash.
______10. Using a pipette, remove some of the strawberry extract from the cup. Carefully
pipette the strawberry extract into the alcohol in the test tube and watch the solution precipitate
(separate).
______11. DO NOT SHAKE THE TUBE!!! Very gently swirl the tube once or
twice. Then let the tube remain undisturbed in the small beaker. You should see
two layers like oil and vinegar make. This takes about 2 minutes. Do not
shake the tube or mix the layers! A white precipitate (solid) should start to
appear.
______12. Slowly add the cold ethanol to the test tube until the test tube is half
full.
______13. It's time to see if we have extracted DNA-so let's
spool! Slide a thin, clean plastic rod (into your test tube until it
penetrates the interface between the layers. Then spool the DNA by rotating
your rod while bringing it up and down gently. Do not stir. Large molecules of
white DNA will precipitate (spool) on the sides of the rod. Reel in a good
clump of fibers. These are not single DNA molecules, but huge ropes of
thousands of molecules twisted together. Place the spooled DNA on the rod in
the empty test tube.
_______14. Clean Up! Throw away your cup, filter, rubber band and bag.
________15. Return Materials: Bring your small beaker with the test tubes,
pipette, and plastic rod to the materials station.
Summary Questions
1. According to this lab, what does DNA look like?
2. A person cannot see a single human hair four classrooms away. But if you wound
thousands of hairs together into a rope, it would be visible at the same distance. How is this
statement an analogy to our DNA extraction?
3. Since the strawberries were once living, and we extracted DNA from them, what does this
mean about the foods you eat?
4. Look at the plant cell pictured to the right. Remember that
genes are found on chromosomes, and genes control traits. Give
at least two examples of traits (characteristics that we can
observe) that are expressed (shown) in the strawberry.
5. If you wanted to extract DNA from a living person, which cells would you use and why?
6. List two reasons why a scientist might want to study the DNA of strawberries.