Download Strawberry DNA Extraction Lab (This promises to be berry interesting!)

Strawberry DNA Extraction Lab
(This promises to be berry interesting!)
Background: DNA is found in the cells of every living organism. DNA is a double stranded
molecule composed of nucleotide bases pairing Adenine with Thymine and Guanine with
Cytosine. Strawberries are soft and easy to pulverize. Strawberries are polyploidy, meaning they
have large genomes with many sets of chromosomes, making them ideal for DNA extraction.
DNA can be extracted from cells by a simple technique using household chemicals enabling
you to see strands of DNA with the naked eye. The soap in the reaction buffer helps to dissolve
the cell membrane and organelles. This helps provide access to the DNA. The salt in the reaction
buffer is used to break up protein chains that bind around nucleic acids. DNA is not soluble (can
not dissolve) in ethanol (isopropyl alcohol). The colder the ethanol, the more the DNA will
precipitate from the solution.
Pre-lab Questions: Discuss these 2 questions in your group.
1. What do you think the DNA will look like?
2. Where is DNA found?
Materials:
1 heavy duty zip-lock baggie
1 large strawberry
Coffee filter
100 ml beaker
Test tube
Stirrer
Reagents: (reagent (rē-ā'jənt) n. A substance used in a chemical reaction to detect, measure,
examine, or produce other substances.)
DNA extraction buffer (soap and salt mixture)
Ice-cold 95% isopropyl alcohol
Procedure:
1. Place one strawberry in a zip lock baggie. Ensure that as much air is pushed out of the baggie as
possible before you close it.
2. “Mush” strawberry inside closed baggie with hands for 3 minutes. This increases the surface area
of the strawberry and allows you to expose and break open many of the cells. DO NOT POUND
BAGGIE! DO NOT BREAK BAGGIE!
3. Add 10 ml (approximately 5 pipettes) of extraction buffer to the bag (salt and soap solution). The
extraction buffer helps to break down the cell membranes and proteins, allowing the DNA to be
“released” from the cells.
4. Close baggie, release air, and gently mush again for two minute.
5. Fold a coffee filter two times in order to make a “funnel.” Open one flap and place the pointy end of
your coffee filter into a plastic cup.
6. Pour your strawberry mush into the coffee filter “funnel.” Allow the liquid to drip into your plastic
cup for about 4 or 5 minutes. If you need additional filtrate, wrap the filter closed and gently squeeze
the contents on the side of the cup so that the liquid continue to drip. Be sure not to rip the filter. The
filter helps to separate the cellulose and bigger components of your contents for the DNA in the liquid.
7. Use a pipette to fill your test tube about 1/3 full with strawberry filtrate.
8. Tilt your test tube slightly and slowly pipette ice-cold alcohol down the inside of the test tube.
(About equal to the amount of the strawberry liquid.) Slowly and very gently rock the tube back and
forth. DO NOT SHAKE THE TEST TUBE or your DNA will fragment.
9. Let the test tube sit for a minute. At the interface (where the strawberry filtrate meets the alcohol),
you will see the DNA precipitate (separate) out of the solution and float to the top. This occurs
because DNA is not soluble in ethanol.
10. Observe the 3 layers within your test tube. The bottom layer contains water and proteins. The
middle layer is whitish and contains your threads of DNA. The upper level is clear.(ethanol – lowest
density so it is at the top.)
11. If you want, you may use your pipette to gently “spool” out your strawberry DNA.
12. NOW, as a group, answer the conclusion and lab analysis questions. ALL members of the group
must be involved in the answering of questions. Your teacher will expect to see the handwriting of
each group member.
Lab adapted from “The Science Behind Our Food” and “Berry Full of Life.”
NAMES: _______________________________________
PER:_________________
Strawberry DNA Extraction Lab
(This promises to be berry interesting!)
Conclusions and analysis:
1. Each step in the procedure aided in isolating the DNA from the other cellular materials. Match the
procedure with its function:
PROCEDURE
A. Filter strawberry mush through coffee filter
FUNCTION
___ To precipitate DNA from solution
B. Mush strawberry with extraction buffer
___ Separate components of the cell
C. First smashing and grinding of strawberry
___ Break open the cells
D. Addition of alcohol to filtered extract
___ Break up proteins and dissolve cell
Membranes
2. Where in the cell can you find DNA?
3. Sketch your test tube after DNA precipitated (comes out of solution). Label the materials found
within the three layers of your test tube.
4. You 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. Explain how this statement relates to
our extraction of strawberry DNA.
5. Why might it be important for scientist to be able to extract DNA from an organism? List two
reasons.
1.
2.
6. Do ALL living or once living cells contain DNA? _________ Is there DNA in your food? _________
What information did you use to answer the above questions?
7. Imagine that you are a farmer who makes a living off of growing and selling your strawberry crops.
What kind of information could strawberry DNA provide you in order to make your business more
successful?
DNA Structure Questions:
8. Sketch a molecule of DNA and label the following parts: sugar, phosphate, adenine, thymine,
cytosine, guanine, and nucleotide.
9. What term is used to describe the shape of a DNA molecule?
10. Nucleotides are the monomers of DNA molecules. What three parts make up a nucleotide
monomer?
1.
2.
3.
Lab adapted from “The Science Behind Our Food” and “Berry Full of Life.”