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Biology LibreTexts

11.2: Procedure

  • Page ID
  • Isolation of DNA from plants

    Wheat germ is obtained from wheat seeds. The germ is the embryo. A seed consists of the embryo surrounded by a seed coat and contains nutrition for the seed. When wheat seeds are milled into white flour, the germ and bran (fiber) are removed. Whole wheat flour contains all parts of the wheat seed. Strawberry seeds also contain large amounts of DNA, a commonly cultivated strawberry, Fragaria ananassa, is octoploid – contains eight sets of chromosomes in each cell.


    • Raw, untoasted, wheat germ
    • 250 ml beaker (2)
    • Strawberries
    • Ice in tray

    • Spatula
    • 50 ml beaker
    • Electronic balance
    • 50 ml graduated cylinder
    • Mortar and pestle
    • Small strainer
    • DNA extraction buffer
    • Wooden rod
    • (water, salt, and detergent)
    • Wax pencil
    • 95% Ethyl alcohol, ice cold

    Lyse plant cells

    1. Make a crease in a piece of weigh paper or weigh boat. Place the weigh paper/boat on the balance and zero the balance. Weigh 1 gram of raw wheat germ. Add the wheat germ to a 250 ml beaker.
    2. Weigh 20 grams of strawberry. Mash thoroughly in a mortar and pestle and add to a separate 250 ml beaker
    3. Use the graduated cylinder to measure 30 ml DNA extraction buffer that has been pre-heated to 60oC.
    4. Swirl mixtures constantly for 5 minutes.
    5. Questions
      1. What occurs to cell membranes when exposed to detergent in the DNA extraction?

      2. Describe cell lysis.

      3. How is the germ of the wheat plant similar to a strawberry seed?

    Filter plant cell extract

    1. Obtain a small strainer and 2 clean 50 ml beakers. . Carefully strain the wheat
      germ extract until 10 ml have been obtained. Repeat for the strawberry extract
      using a separate beaker.

    2. Discard the solid plant remnants (regular trash).

    3. Questions

      1. List 3 molecules that have passed through the cheesecloth into the filtrate

      2. On what molecular basis does filtration select - charge, solubility, size, density?

      3. Where is the plant DNA now located?

    Precipitate DNA

    1. Use a graduated cylinder to measure 2X volume (20 ml) ice-cold ethanol. Slowly pour the ethanol down the side of each beaker so that the ethanol is layered over the filtrate. DO NOT MIX.
    2. Let the preparation sit undisturbed for up to 5 minutes. Observe the interface.
    3. Sketch one of the beakers. Label: ethanol, filtrate, DNA at interface.

    Spool DNA

    1. Spool DNA from one of the beakers onto a wooden rod. Obtain as much DNA as
      possible on the rod. Lift the DNA out of the solution and blot the excess alcohol on a
      paper towel.

    2. Describe the appearance of the DNA in terms of color and substance

    3. What is the role of ethanol in the DNA extraction procedure?

    4. Use a wooden rod to spool the DNA as demonstrated by the instructor.

    Record Observations (the appearance of DNA and other observations during spooling)