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Life Science: Session 3

Teaching Tips: DNA Extraction

kiwi fruit

One characteristic of DNA that makes it difficult to observe—and make observable to students—is its size. DNA is a molecule that is about 1 million times smaller than a millimeter! In the video, this molecule was made visible by extracting a great amount of it from the cells of a Kiwi fruit—which has cells that make this easy. This is a summary of how to extract DNA and make it visible in this way.

This information was gathered from the following Web sites:

  • http://www.ba-education.demon.co.uk/for/science/dnamain.html
  • http://www.steve.gb.com/science/fruitful_dna.html

Materials Needed

  • a ripe Kiwi fruit
  • ice cold isopropyl (or other) alcohol
  • table salt
  • liquid dishwashing detergent
  • a knife and cutting board
  • a metric scale
  • a graduated cylinder
  • a jug
  • a small bowl.
  • a large saucepan full of hot water (not boiling — about 60 degrees)
  • a large saucepan full of ice
  • a coffee filter and filter funnel.
  • a test tube
  • some thin wire

Instructions

  1. Put the bottle of alcohol in the saucepan of ice.
  2. Make up an extraction solution of 3 grams of salt, 10 ml of detergent and 100ml of water.

    kiwi DNA step 2
  3. Stir thoroughly to dissolve the salt, but avoid froth.

    kiwi DNA step 3
  4. Peel and chop one Kiwi fruit. Scoop this into the small bowl and add 100 ml of the extraction solution.

    kiwi DNA step 4
  5. Put the bowl containing the mixture into the saucepan of hot water and leave for 15 minutes.

    kiwi DNA step 5
  6. After 15 minutes pour the mixture into the coffee filter, and catch the liquid that filters through in the test tube. This will form a green layer.

    kiwi DNA step 6
  7. Very carefully drizzle the ice cold alcohol down the side of the test tube so that it forms a purple layer on top of the green layer. Add about the same amount of alcohol as there is in the first layer.

    kiwi DNA step 7
  8. Let the test tube stand for a few moments. You should see a white layer beginning to form at the boundary between the green and the purple layers. If you have done it correctly you will see that the layer is made up of a filament — DNA from Kiwi fruit.

    kiwi DNA step 8
  9. Try scooping the DNA out with a loop of thin wire—this thick, translucent substance is the molecule of life.
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