BOSS Biology
BERRY FULL OF DNA
Pre-Lab:
Read over the Lab Procedures on the following pages and complete questions #1-4.
1) Purpose:
2) What do you think the DNA extracted will look like? How much DNA do you think you will get from one strawberry?
3) Are there any safety considerations for this lab investigation?
4) Using a flow-chart (or diagrams), outline the procedures that need to be followed for this lab.
Materials: (per 2-3 students in a group)
Equipment:
1. 1 heavy duty zip-lock baggie
2. 1 strawberry (fresh or frozen and thawed)
3. cheesecloth
4. funnel
5. 100 ml beaker
6. 50 ml beaker
7. wooden coffee stirrer
Reagents:
1. DNA extraction buffer (One liter: mix 100 ml of shampoo (without conditioner), 15 g NaCl, 900 ml water OR 50 ml liquid dishwashing detergent, 15 g NaCl and 950 ml water)
2. Ice -cold 95% ethanol or 95% isopropyl alcohol
Procedure:
1. Place one strawberry in a zip lock baggie.
2. Smash strawberry with fist for 2 minutes.
3. Place the strawberry slurry in the 100ml beaker.
4. Add 10 ml extraction buffer.
5. Mush again for two minutes with the stirring rod. Try not to create bubbles.
6. Filter through cheesecloth in a funnel into 50 ml beaker to get at least 10-15ml of slurry.
7. Slowly pour the ice-cold alcohol into the beaker until about 35-40ml is full
8. At the interface, you will see the DNA precipitate out of solution and float to the top. You may spool the DNA on your glass rod (after you rinse it).
Questions:
1. Where can DNA be found in the cell? What did the DNA extracted in this experiment look like? Colour? Shape? Size? Consistency? How do you think its structure may affect the way it looks when clumped together? Were you surprised by its appearance?
2. Commercial strawberries are octoploid (8n), so each cell has eight of every kind of chromosome. Why are strawberries a good choice for this experiment?
3. Discuss the action of the soap (detergent) on the cell. What is the purpose of the soap in this activity?
4. What was the purpose of the Sodium Chloride (salt), include a discussion of polarity and charged particles?
5. DNA is soluble in water, but not in ethanol. What does this fact have to do with our method of extraction? Explain what happened when the ethanol came in contact with the strawberry extract.
6. What could you do differently to increase the yield and purity of the DNA sample? What are some sources of error that may have stopped you from getting the exact amount of DNA in each strawberry
7. Would this protocol work on food that has been heated or cooked to a high temperature? Why/Why not?
8. In order to study our genes, scientists must first extract the DNA from human tissue. Would you expect the method of DNA extraction to be the same for Human DNA? Why or why not?
9. Would the DNA be the same in any cell in the human body?
10. Suggest two reasons why scientists might want to study the DNA of strawberries.
11. What did the DNA look like? Relate its chemical structure to how it looks when lots of it is clumpedtogether.
The DNA looked like spider webs. The DNA precipitate look like long and thin fibers. This makes sense
since the molecular structure is so long and narrow.
2. DNA is soluble in water, but not in ethanol. What does this fact have to do with our method of
extraction? Explain what happened when the ethanol came in contact with the strawberry extract.
The DNA was soluble in the DNA extraction buffer so we could not see it. When it got stirred into the
ethanol, it clumped together and formed thicker and thicker strands large enough to see.
3. 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 at some distance. How is this statement an analogy to our
DNA extraction?
DNA is far too narrow to see, but if there are many thousands of strands together, it is thick enough to be
visible
4. In order to study our genes, scientists must first extract the DNA from human tissue. Would you
expect the method of DNA extraction to be the same for Human DNA? Why or why not?
Animal cells do not have cell walls. It won’t be necessary to filter out the cellulose debris. Also, animal
cells can be lysed if put in hypotonic solution.
5. Would the DNA be the same in any cell in the human body?
Since we were once one cell and grew to an organism by mitosis, all of the DNA in our cells is identical.
6. If you wanted to extract DNA from a living person, what cells would you use and why?
Blood is the easiest tissue to obtain from living humans. White blood cells contain a nucleus, while red
blood cells do not. Skin cells would also work if only a small amount of DNA were needed.
7. List two reasons why a scientist might want to study the DNA of strawberries.
Scientists might want to compare the DNA of a type of strawberry that is more disease or frost resistant
than other strawberries
Scientists may want to study the evolutionary relatedness of strawberries to other berries.
Scientists may want to study a gene that codes for a particular protein in strawberries. For example,
strawberries are known to have some chemical in them that slows the growth of some tumors.
Scientists may want to clone a particular gene in strawberries. Perhaps they want to make large quantities
of the protein that makes strawberries red or produces the desired flavor of strawberries.
Adapted from: http://carnegieinstitution.org/first_light_case/horn/DNA/BERRYteacDNA and http://www.ncsu.edu/kenanfellows/2002/pligon/biotech/labs/strawberry.html