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Strawberry DNA

Cheek Cell DNA
The purpose of this lab is to attempt to Isolate DNA from Strawberries. In doing so you will experience some of the steps taken by scientists to acquire DNA which could be used in a variety of experiments. The Human DNA analyzed as part of the Human Genome Project was isolated in a similar way. If the amount of DNA recovered is extremely small, say perhaps from a crime scene or from an extinct life form, many millions of copies must first be made of that which was recovered by using PCR technology. Having millions of copies would be needed to run experiments that will reveal the makeup of the DNA collected.We will talk about the process of PCR technology at a later time. For now.....let's isolate!


Strawberries Bamboo skewer
Paper Towel H2O
Dish soap Funnel
Table salt Small ziplock bag
Rubbing alcohol Test Tube

Make Sure ALL Glassware is SQUEKY CLEAN before mixing any reagents.

1. Place 1-2 large strawberries into a small ziplock bag and crush the berries until pulpy (about 1-2 minutes). Have the other member of your lab team make the lysis buffer while the strawberry is being crushed.

2. Make the lysis buffer in a cup by combining

  • 10 mL of water
  • 1⁄2 Teaspoon Dish soap
  • 1⁄2 Teaspoon salt

3. Place 2 Teaspoons Lysis Buffer into the bag and mix for about a minute.

4. Pour the strawberry mixture into a funnel lined with paper towel into a test tube and SQUEEZE the mixture into the tube. Make sure that all strawberry extract passes through the paper towel before entering the test tube. This will insure that large particles are strained out of extract.

5. Add an equal or slightly greater volume of rubbing alcohol into the test tube to at least double the volume of the strawberry mush.

6. Place a bamboo skewer into the tube and watch very carefully as you SWIRL the stick.

7. Show me your results.

Questions:(use the web for help if needed)

  1. What is a lysis buffer?
  2. What was the purpose of including dish soap in the lysis buffer?
  3. Why was rubbing alcohol added to the test tube with the strawberry extract?
  4. Briefly describe what the DNA looks like in your test tube.
  5. What purpose does the bamboo skewer serve?
  6. If your DNA sample was tested for the presence of Nitrogen what would the results be? Explain your answer.
  7. Using the web for help briefly describe how a PCR machine (aka: thermal cycler) works.
  8. What are restriction enzymes?
  9. What is meant by Recombinant DNA?
  10. Why would "sticky end" cutting restriction enzymes be used when attempting to move DNA from one organisms to another?
  11. Why must the same "sticky end" cutting restriction enzyme be used on both sources of DNA when attempting to create Recombinant DNA?
  12. When a large amount of DNA is mixed with restriction enzymes RFLPs are formed. What is meant by RFLP?
  13. What biotech protocol is used to seaparate RFLPs?
  14. How does gel electrophoresis allow for the creation of a DNA fingerprint.
  15. You are a CSI Investigator and you have collected tissue from underneath the fingernails of a crime victim. Detectives have apprehended two individuals who both had motive and no alliby. Briefly describe the steps you would take (in correct order) to determine which of the suspects (if any) may have commited the crime.

Visit the following web site and check your understanding of how to make a DNA fingerprint.

Cheek Cell DNA Extraction

Individual strands of DNA are too small to be visible to the eye. One million threads of DNA fit onto the period at the end of a sentence using Times New Roman, font 12 in WORD. The reason why we are able to see DNA in this activity is that there are so many of them, clumped together.

DNA extraction is a fairly simple procedure that requires only a few steps: 1. The detergent breaks open the cells by destroying the fatty membranes that enclose the cells as well as the nuclei membranes within the cells. DNA is released into the solution. Detergent and the salt also helps strip away proteins that are associated with the DNA molecules. 2. DNA is NOT soluble in alcohol, whereas other cell parts are. By adding alcohol, DNA precipitates out of the solution and collects at the interface of the alcohol and soap layer. The colder the alcohol, the less soluble the DNA will be in it.



  1. A 0.9 percent salt solution (2 teaspoons of table salt dissolved in 1 quart/liter of water) is in a Alhambra Jug in the back of the room.
  2. Pour saline solution in one of the small plastic cups appx 1/6 full (see image on white board)
  3. Swirl the 10ml of salt solution in your mouth for 30 seconds. This will remove dead cells lining the mouth.
  4. Carefully spit solution back into the small plastic cup and then pour as much of the solution as is possible it into the reaction tube. Pour off excess into the sink. Flush the sink with water and be sure to throw the plastic cup into the trash.
  5. Bring reaction vessel to me at the centrifuge 20 minutes before the bell rings.
  6. Collect your reaction vessel and look at the very bottom for a small ball of cells.
  7. Carefully pour off as much of the content WITHOUT DISRUPTING OR LOSING THE BALL OF CELLS.
  8. Prepare 25 percent detergent solution (1 drop detergent 3 drops of water)
  9. Add detergent solution into plastic reaction vessel.
  10. Gently rock reaction vessel back and forth for 30 seconds to a minute. DO NOT SHAKE VESSEL VIGOROUSLY. THIS WILL BREAK UP THE DNA AND MAKE IT HARDER TO SEE.
  11. Fill the remainder of the vessel with rubbing alcohol using your pipette.
  12. The alcohol and the detergent should form two distinct layers with the alcohol sitting on top.
  13. Let the tube stand for one minute and then use cofee strirrer to slowly move some of the ethanol into the soap layer. DNA will start to precipitate out of the soap solution. Twirl the stirrer to spool the DNA strands around it.
  14. If you wish to take your DNA home come to me for a new reaction vessel to transfer the DNA into.