Objective: To extract DNA from strawberries        

Background: All living cells contain DNA. DNA provides unique genetic characteristics of organisms, that is, how they look and how they behave. To study DNA we first have to extract it from the cell. In this lab, you will learn how to extract DNA from a plant source, which in this case will be strawberries. Strawberries are an excellent source for DNA extraction since they contain eight copies of each chromosome. In addition, they can be easily mashed and contains enzymes that break down cell walls, providing easier access to the nucleus.

Materials:

  • DNA extraction buffer (Contains 100 ml detergent and 15g NaCl per liter of distilled water)
  • 95% ethanol
  • Ice
  • Strawberries
  • Ziploc bags
  • 150 ml beaker
  • Test tubes
  • Test tube rack
  • 10 ml measuring cylinder
  • Pipette
  • Strainer
  • Glass rods
  • Petri dish

Procedure:

  1. Remove green sepals from strawberries
  2. Place three (3) strawberries into a Ziploc bag and seal
  3. Squish strawberries for a few minutes to completely squash the fruit
  4. Add 10 ml of DNA extraction buffer and squish for another 2 minutes. Note: avoid making a lot of soap bubbles. You can do this by squeezing out air before you resume squishing
  5. Filter into 150 ml beaker using fine-sieve kitchen strainer provided
  6. Measure 3 ml extracted liquid with a 10 ml measuring cylinder and transfer to a beaker
  7. Rinse and drain the measuring cylinder and use it to measure 3 ml of 95% ethanol (you may use a pipette dropper to transfer ethanol to cylinder)
  8. Hold the test tube at an angle and slowly add the 3 ml 95% ethanol
  9. Allow to sit for 2 minutes
  10. By the end of the 2 minutes you should see a white fluffy cloud at the interface of the extract and the ethanol. This contains a tangle of DNA
  11. Slowly rotate a glass rod at the interface of the liquids to trap and remove the DNA
  12. Place the DNA on a petri dish. This sample contains millions of DNA strands

Lab Questions

  1. Briefly explain the role of DNA in living systems (Include a labelled structure of a DNA molecule)
  2. What is the purpose of the following materials used in the experiment?
    1. Detergent
    1. Sodium chloride
    1. Ethanol
  3. Strawberry chromosomes are octoploid. What does this mean? Are the chromosomes in humans arranged the same way? If not, what is the difference?

Courtney Simons
Administrator
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
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