BERRY FULL OF DNA
DNA EXTRACTION LAB
QUESTION: How do the physical properties of strawberry DNA relate to the structure of DNA
molecules?
LAB OVERVIEW: You will observe the physical properties of DNA. You will break open strawberry cells,
prepare a filtered extract containing strawberry DNA, and separate out molecules of DNA in a test tube.
Please write your hypothesis for the following: Why is the DNA extraction lab relevant to your
understanding of the structure of DNA?
HYPOTHESIS: _________________________________________________________________________
INTRODUCTION: Strawberries are a good source of DNA because they have 8 copies of each type of
chromosome. You’ll never be able to eat a strawberry again without thinking about how much DNA is in
it!
PROCEDURES:
1. Place one strawberry in a Ziploc bag. Press the air out and seal it. Mash the Ziploc bag with
your hands for 2 minutes.
2. Add 10ml of blue DNA extraction buffer to the bag. Press the air out and carefully seal the bag.
3. Mash the Ziploc bag again for 1 minute.
4. Set up filtration apparatus using test tube, funnel, and cheese cloth.
5.
6.
7.
8.
9.
10.
11.
Cut off the bottom corner of the bag and squeeze the squished strawberry liquid onto the
filtrations apparatus that you’ve setup. Let it drip directly into the test tube.
When the test tube is about a centimeter full, take the funnel out of the test tube. Discard any
extra mashed strawberry pulp in the trash.
Clean the cheesecloth and lay flat to dry.
Slowly drizzle cold ethanol from a pipette down along the side of the test tube until you have
equal amount of strawberry extract and ethanol on top. The ethanol should forma distinct layer
on top of the filtered extract.
The DNA should form a web-like layer where the strawberry extract and the ethanol meet.
Use the inoculating loop to swirl the DNA onto the loop. Do NOT stir or shake up the tube. It
must be still for the DNA to stay suspended in the ethanol.
Notice the characteristics of the DNA as you swirl it onto the inoculating loop.
ANALYSIS AND CONCLUSION:
1. What did the DNA look like?
2.
Where can DNA be found in the cell?
3.
Relate the chemical structure of DNA to the way it looks when its clumped together.
4.
DNA is soluble in water, but NOT in cold ethanol. Why does this fact help in the extraction
method you used in lab today?
5.
A person cannot see a single cotton thread from 100ft. away, but if thousands of threads
are wound together into a rope, the rope can be seen at some distance. How does this
statement compare to the DNA extraction you just completed?
6.
In order to study human genes, scientists must first extract the DNA from human tissue
cells. Would you expect the method of DNA extraction for human DNA to be the same as
the method you used to extract DNA from strawberries? Why?
7.
Would the DNA be the same in any cell in the human body? Hint: Remember that every
person starts out as one fertilized cell.
8.
If you wanted to extract DNA from a living person, could you use red blood cells? Why or
why not?
9.
Is there DNA in the food you eat?_______ How do you know?
10. Match the procedure with what it is doing to help extract the DNA from other cell materials
_______ Break open cells
_______ Break proteins & dissolve cell
A. Initial squishing of strawberry
membranes
B. Filter DNA extract thru cheesecloth
_______ Precipitate (clump) the DNA
C. Mix in DNA buffer solution
_______ Separate organelles, broken cell
D. Layer cold ethanol over DNA extract
walls, and membrane from DNA
11. Write a C.E.R. (claim, evidence, reasoning) conclusion as to why this lab is relevant to the
understanding of the structure of DNA. You may mention things such as what the DNA
looked like in the test tube and what properties you observed with the unaided eye.
TEACHER PREP PAGE and ANSWERS!
The purpose of each ingredient in the procedure is as follows:
Shampoo or dishwasher soap helps to dissolve the cell membrane, which is a lipid
bilayer.
Sodium chloride helps to remove 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. 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.
To make DNA Extraction Buffer:
• 100 ml dishwasher detergent
• 15 grams unionized sodium chloride (2 teaspoons)
• 900 ml distilled water
ANALYSIS AND CONCLUSION:
1.
2.
3.
4.
5.
6.
7.
8.
What did the DNA look like?
Answers will vary
Where can DNA be found in the cell?
In the nucleus
Relate the chemical structure of DNA to the way it looks when its clumped together.
Answers will vary. Discuss DNA clinging to itself so it clumps together, can’t see double
helix because its too small.
DNA is soluble in water, but NOT in cold ethanol. Why does this fact help in the
extraction method you used in lab today?
Since it doesn’t dissolve in ethanol, it will separate out and be visible.
A person cannot see a single cotton thread from 100ft. away, but if thousands of
threads are wound together into a rope, the rope can be seen at some distance. How
does this statement compare to the DNA extraction you just completed?
Can’t see the DNA from one cell, but from many cells you can.
In order to study human genes, scientists must first extract the DNA from human tissue
cells. Would you expect the method of DNA extraction for human DNA to be the same
as the method you used to extract DNA from strawberries? Why?
Yes, same extraction method will work
Would the DNA be the same in any cell in the human body? Hint: Remember that every
person starts out as one fertilized cell.
Yes, DNA in all cells in the same individual is the same.
If you wanted to extract DNA from a living person, could you use red blood cells? Why
or why not?
No, red blood cells have no nucleus.
9.
Is there DNA in the food you eat?_yes__ How do you know? Eating plants or animals,
their cells contain DNA
10. Match the procedure with what it is doing to help extract the DNA from other cell
materials
__A____ Break open cells
__C____ Break proteins & dissolve cell
A. Initial squishing of strawberry
membranes
B. Filter DNA extract thru cheesecloth
__D____ Precipitate (clump) the DNA
C. Mix in DNA buffer solution
__B____ Separate organelles, broken cell
D. Layer cold ethanol over DNA extract
walls, and membrane from DNA
11. Write a C.E.R. (claim, evidence, reasoning) conclusion as to why this lab is relevant to
the understanding of the structure of DNA. You may mention things such as what the
DNA looked like in the test tube and what properties you observed with the unaided
eye.
My hypothesis, ______(restate hypothesis here)___________, was/was not supported.
My data shows that_____________________________________________.
This may be due to______________________________________________.