Detection of DNA

Overview

In this activity, you will confirm that the substance extracted from the fruit is indeed DNA. DNA can be identified chemically with the Dische diphenylamine test. Acidic conditions convert deoxyribose to a molecule that binds with diphenylamine to form a blue complex. The intensity of the blue color is proportional to the concentration of DNA. The Dische’s test will detect the deoxyribose of DNA and will not interact with the ribose in RNA. The amount of blue corresponds to the amount of DNA in solution.

The diphenylamine compound of the Dische’s test interacts with the deoxyribose of DNA to yield a blue coloration.

Materials

Each lab group will need the following materials:

  • DNA from the previous activity
  • Dische’s diphenylamine reagent
  • distilled water
  • 3 test tubes
  • test tube rack
  • hot plate
  • large beaker filled with water
  • test tube clamp
  • wax pencil

Method

  1. Obtain 3 test tubes and number them 1-3.
  2. Suspend the spooled DNA in 3 ml of distilled water. MIX.
  3. Add to tubes:
    1. 2 ml of DNA solution
    2. 1 ml of DNA solution with 1 ml H2O
    3. 2 ml of H2O
  4. Add 2 ml of the Dische’s diphenylamine reagent to each tube and mix thoroughly.
  5. Place in a boiling water bath for 10 minutes.
  6. Evaluate your results. A clear tube indicates no nucleic acids. A blue color indicates the presence of DNA. A greenish color indicates the presence of RNA.
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