Name ______________________ Date _____ Period ______
Partner _______________________
Strawberry DNA Extraction Lab
1) List what you know!
What do you know about strawberries?
What do you know about DNA?
2) List what you want to know!
What do you want to know about
strawberries?
What do you want to know about DNA?
PERRY 2011-2012
Name ______________________ Date _____ Period ______
Partner _______________________
Strawberry DNA Extraction Lab
Introduction
Have you ever wondered what DNA looks like? You are going to break apart the
cell membrane of a strawberry and separate the DNA from the nucleus.
Since DNA is the blueprint for life, everything living contains DNA. DNA
isolation is one of the most basic and essential techniques in the study of DNA.
The extraction of DNA from cells and its purification are of primary importance
to the field of biotechnology and forensics. Extraction and purification of DNA
are the first steps in the analysis and manipulation of DNA that allow scientists
to detect genetic disorders, produce DNA fingerprints of individuals, and even
create genetically engineered organisms that can produce beneficial products
such as insulin, antibiotics, and hormones.
DNA can be extracted from many types of cells. The first step is to lyse, or
break open, the cell. This can be done by grinding a piece of tissue. After the
cells have broken open, a salt solution such as NaCl and a detergent solution
can be added. These solutions break down and emulsify the fat and proteins
that make up a cell membrane. The soap helps to dissolve the phospholipid
bilayers of the cell membrane and organelles. The salt is used to break up
protein chains that bind around the nucleic acids. Finally, ethanol is added.
DNA is soluble in water, but not ethanol. The colder the ethanol, the less
soluble the DNA will be. The alcohol causes DNA to precipitate, or settle out of
the solution, leaving behind all the cellular components that aren’t soluble in
alcohol. The DNA can be spooled, or wound, on a stirring rod and pulled from
the solution at this point.
Strawberries are soft and easy to pulverize. Strawberries have large genomes;
they are octoploid, which means they have eight of each type of chromosome in
each cell. Thus, strawberries are an exceptional fruit to use in DNA extraction
labs.
PERRY 2011-2012
Materials:
-fresh strawberries
-large Ziploc bag
-table salt
-meat tenderizer
-beaker
-cheese cloth
-rubber band
-skewer stick
-ethanol
Procedure
1) Take 1-2 strawberries (with green top removed) and place in Ziploc bag. Seal the
bag, pushing all excess air out.
2) Gently mash strawberries with hands for ~ 2 minutes or until strawberries are
pulverized.
**Be careful not to bust the bag! Strawberry juice does stain clothes!
3) Open Ziploc and put 1-2 large pinches of salt inside.
4) While bag is still open, put several shakes of meat tenderizer into bag.
5) Seal bag and mix contents by squeezing contents around bag.
6) When the contents of the bag is thoroughly mixed, squeeze all of contents to the
bottom corner of the bag. Wait 3-4 minutes.
7) While you are waiting, take your beaker and place the cheesecloth on top. Keep
the cheese cloth on top by using the rubber band around the beaker. Make sure
there is a divot in top to hold the contents of your bag. Do this by pushing down
on the cheesecloth with your finger. Divot should be no more that ½- ¾ inches
at most. When you are finished with this step show Ms. Perry.
8) Have Ms. Perry cut your Ziploc bag at the corner. Then, squeeze out contents of
bag into cheesecloth.
9) Wait 3-4 minutes for contents to drip out, then ask Ms. Perry to pour ethanol
through the cheesecloth.
10) Remove the cheese cloth from the beaker.
11) Observe the solution. What changes are happening?
___________________________________
12) After ~ 1 minute, use your skewer stick and move around solution. Twirl stick
around to wind up material. Observe material on stick.
PERRY 2011-2012
Strawberry Extraction Lab Questions
1)
Where in the cell is DNA found?
2)
Match the procedure with its function:
PROCEDURE:
FUNCTION:
A. Filter strawberry slurry through cheesecloth
___To precipitate DNA from solution
B. Mush strawberry with salty/soapy solution
___ Separate components of the cell
C. Initial smashing and grinding of strawberry
___ Break open the cells
D. Addition of ethanol to filtered extract
___ Break up proteins and dissolve cell
membranes
3) What did the DNA look like? Does it have any color? Relate what you know about the
chemical structure of DNA to what you observed today.
4) Explain what happened in the final step when you added ethanol to your strawberry extract.
5) 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 much further away. Is this statement analogous
to our experiment? Explain your answer.
6) Why is it important for scientists to be able to remove DNA from an organism? List two
reasons.
7) Is there DNA in your food? How do you know?
8) The human body contains about 100 trillion cells. If each cell contains approximately 6 feet of
DNA when stretched out, how many feet of DNA does our body contain?
PERRY 2011-2012