DNA EXTRACTION: A BERRY FULL OF DNA
BACKGROUND:
DNA (deoxyribonucleic acid) is located in the cells of all living organisms. The DNA molecule directs the
synthesis of every protein and contains all the genetic information that is passed on to new cells. Although DNA is
an incredibly small molecule, in large quantities, it can be seen.
In this activity, you will extract DNA from a strawberry. One of the
reasons strawberries work so well is that they are soft and easy to pulverize.
Also, ripe strawberries are producing pectinases and cellulases, which are
already breaking down the cell walls. Most interestingly, strawberries have
enormous genomes. They are octoploid, which means they have eight of each
type of chromosome.
There are three basic steps in DNA extraction.
 First, the cell must be lysed (broken open) to release the nucleus.
 Next, the nucleus must also be opened to release the DNA.
 Lastly, once the DNA is released, it must be precipitated out of
solution.
Several reagents are required to complete the extraction procedure—salt, detergent, and alcohol. Both
the cell and nuclear membranes are composed primarily of lipids. In order for the cell to be lysed, the lipid walls
must be broken down. The manual grinding and detergent solutions accomplish this. Soap molecules mix with
fats or lipids, causing structures made of lipids to break apart. Ethanol is used to precipitate the DNA. In water,
DNA is soluble. When it is in ethanol, it uncoils and precipitates .The addition of salt solution provides the DNA
with a favorable environment by contributing positively charged atoms that neutralize the normal negative charge
of the DNA, allowing the DNA to clump together.
MATERIALS (PER STUDENT GROUP OF 2):
 Sandwich sized zip-lock baggie
 1 strawberry (fresh or frozen)
 10 ml DNA extraction buffer
 Ice cold ethanol
 Transfer Pipets
 Test tube
 Graduated Cylinders (10 ml)
 Bamboo skewer
 Filtering Apparatus:


Extraction Buffer Recipe (100ml)
2 grams of NaCl (Salt)
10 ml of Dawn
90ml of DI Water
Cheesecloth
Funnel
PROCEDURE:
1. Place one strawberry in a Ziploc Baggie and zip it closed. (Make sure to remove extra air)
2. Smash up the strawberry with your hand and finger for 2 minutes.
3. Add 10ml of the Extraction Buffer you made to the bag and zip it closed; Mush again for 1 minute
4. Pour the mush through the cheese cloth and let it drip into the beaker
5. Add filtered strawberry liquid into a test-tube until it is 1/4 full.
6. Slowly drip cold ethanol (rubbing alcohol) down the side until the test-tube is 1/2 full.
7. Hold the test tube at the top so you don’t heat up the liquid/ethanol.
8. Dip the bamboo skewer (with a bent tip) into the test-tube right where the alcohol and extract layers meet,
spool the DNA by spinning and wrapping it around the tip.
Name __________________________________________
Period _________
DNA EXTRACTION: A BERRY FULL OF DNA (25 Points)
ANALYSIS QUESTIONS: ALL ANSWERS MUST BE IN COMPLETE SENTENCES TO GET CREDIT
1. What did the Strawberry DNA look like?
2. What is the function of DNA?
3. What does the term octoploid mean?
4. Are strawberry cells prokaryotic or eukaryotic cells?
5. Where would the DNA be located in eukaryotic cells?
6. Where would the DNA be located if this was a prokaryotic cells?
7. What are the three basic steps for DNA extraction?
a. _________________________________________________________________________________
_________________________________________________________________________________
b. _________________________________________________________________________________
_________________________________________________________________________________
c. _________________________________________________________________________________
_________________________________________________________________________________
8. What enzymes naturally are breaking down the strawberry cells?
9. What part of the strawberry cells are they breaking down?
10. What is the purpose of the salt solution in this experiment?
11. Why was detergent added to the extraction buffer?
12. Why does the DNA rise to the top after addition of the alcohol?
13. If you wanted to extract DNA from a living person, what cells would you use and give a reason WHY?
14. Thinking back to the what you learned in the cell division unit, would the DNA be the same in any cell in
the human body? Explain why or why not.
15. List two reasons why a scientist might want to study the DNA of strawberries.
16. A person cannot see single cotton thread 100 feet away, but if you wound thousands of threads together into
a rope, it would be visible at some distance. How is this statement an analogy to our DNA extraction?