Name______________________________ Date________________
DNA Extraction: Strawberry
Background: The long, thick fibers of DNA store the information for the functioning of the
chemistry of life. DNA is present in every cell of plants and animals. The DNA found in
strawberry cells can be extracted using common, everyday materials.
We will use an extraction buffer that is made up of salt and soap to help isolate DNA from a
strawberry cell.
Some of the items/conditions used in this lab are listed below with their purpose.
Shampoo or dishwasher soap *found in buffer helps to dissolve the lipids found on the cell
membrane and nuclear membrane
Sodium chloride (salt) *found in buffer helps to dissolve proteins that are bound to the DNA. It
also helps to keep the proteins dissolved in the aqueous layer so they don’t precipitate in the
alcohol along with the DNA.
Ethanol or isopropyl alcohol causes the DNA to precipitate because it does not dissolve in
alcohol. When DNA comes out of solution it tends to clump together, which makes it visible.
The long strands of DNA will wrap around the stirrer or transfer pipet when it is swirled at the
interface between the two layers. The more concentrated the rubbing alcohol, the less likely
DNA will dissolve in it.
Meat Tenderizer: used to help break down proteins and to destroy an enzyme known as
protease that can break DNA into small pieces.
Temperature: it is important to keep the alcohol cold so that DNA will dissolve in it better. For
best results, it is best to keep on solutions used in the lab cold.
Pre-lab questions:
1. What do you think the DNA will look like?
2. Where in the cell is DNA found?
3. Why do you think it is important to dissolve the proteins around the DNA?
4. What does it mean to precipitate? Why does DNA precipitate out in rubbing alcohol?
Materials:
heavy duty ziploc bag
1 strawberry (frozen)
20 mL DNA extraction buffer (soapy, salty water)
cheesecloth
funnel
50mL vial / test tube
glass rod, inoculating loop, or popsicle stick
15 mL ethanol
Procedure:
1. Place one strawberry (2 if they are small) in a Ziploc bag.
2. Smash/grind up the strawberry using your fist and fingers
for 2 minutes. Careful not to break the bag!!
3. Add the provided 20mL of extraction buffer (salt and
soap solution) and a PINCH of meat tenderizer to the bag.
4. Kneed/mush the strawberry in the bag again for 1 minute avoiding too many bubbles.
5. Assemble your filtration apparatus as shown to the right.
6. Pour the strawberry slurry into the filtration apparatus and let it drip directly into your
test tube. Fill about half way with liquid.
7. Slowly pour cold ethanol into the tube by gently tipping the test tube (see teacher
instructions)
8. Dip the loop or glass rod into the tube where the strawberry extract and ethanol layers come
into contact with each other.
9. Show your results to the teacher and get a signature ________________________
Your Turn!
You are now going to create a procedure that you believe may alter the amount of DNA that is
extracted. The more creative, the better! You may remove a step, alter a step, or add a step.
Remember, good scientists only change on variable at a time. In the space below, rewrite the
procedure you are going to use step-by-step. Make sure you highlight the change you are
making to the original procedure. Once you finish writing your new procedure, you must write
a hypothesis explaining what you think is going to happen and WHY! Before you perform your
new procedure, you must get teacher approval.
NEW PROCEDURE *you may use additional paper
HYPOTHESIS (MAKE SURE YOU INDICATE WHY)
Teacher signature____________________________________________
Conclusions:
1.
Did the data support your hypothesis? Explain. If not, why do you think the results did not
match your prediction?
2.
Do you think you could use a similar procedure with animal cells? Explain.
3.
Based on the introduction, there was nothing said about breaking the cell wall of the strawberry
cells. What part of the procedure to you believe helped to break up the cell wall?
4.
A student was attempting to follow the procedure step-by-step but forgot to complete one of
them. When the lab was complete, he saw DNA, but it did not look like a long thread. Instead,
it was chopped up into small pieces. What did the student forget to add? Explain.