DNA Isolation From Strawberries

Materials per Student Group:

  • 1-3 strawberries (about the volume of a golf ball). Frozen strawberries should be thawed at room temperature.
  • 10 ml DNA extraction Buffer (soapy, salty water)
  • About 20 ml ice cold 91% or 100% isopropyl alcohol
  • 1 ziplock bag ( freezer bags quart size)
  • 1 clear test tube
  • 1 funnel lined with a moistened paper towel
  • 1 coffee stirrer or transfer pipet

Directions

  1. Remove green sepals from the strawberries.
  2. Place strawberries into baggies and seal shut.
  3. Squish strawberries for a few minutes to completely squash the fruit.
  4. Add 10 ml DNA extraction buffer and squish for a few more minutes. Try not to make a lot of soap bubbles.
  5. Filter through a moistened paper towel set in funnel, and collect the liquid in a clear test tube. Gently squeeze the paper towel with thumb and forefinger. Collect about 3 ml of liquid.
  6. Pour ice cold isopropyl alcohol down the side of the test tube until the alcohol is approximately 2 cm from the top of the test tube. The alcohol should form a separate layer on top of the strawberry fluid.
  7. Watch for about a minute. What do you see? Answer questions 1 of your lab questions.
  8. Insert the coffee stirrer and spin it in the white fluffy cloud of DNA wrapping it around the stirrer.
  9. Pull out the stirrer and transfer the DNA to a clean slide. Gently stretch it apart using 2 toothpicks.
  10. Examine the DNA under the microscope and answer questions 2 & 3.
  11. Add one very small drop of methlyne blue stain to the DNA and examine it under the microscope again. Answer questions 4 & 5
  12. Clean up

Strawberry DNA Lab Questions

PRE-Lab Question

  1. What are the two types of nitrogenous bases?
  2. What two Base pairs go together.
  3. What is the backbone of DNA composed of?
  4. What does DNA stand for?
  5. What is the sugar in DNA called?
  6. What does the sugar in DNA do?
  7. How are the two bases linked together?

Lab Questions

  1. When you added the ice cold Isopropyl Alcohol into the test tube, describe in detail what changes you saw occurring.
  2. While examining the DNA under the microscope, describe the appearance of the DNA before it is stained.
  3. Draw the unstained DNA
  4. Now describe the appearance of DNA after it is stained.
  5. Draw the stained DNA, note any differences you saw in the stained and unstained DNA.