Banana DNA extraction Experiment

This DNA extraction is simple and works every time but the DNA is not pure. Some of the protein is still present. However, it is nice because the students get to see and hold in their hand the substance they have been studying that seems so abstract and hard to believe it even exists.

Materials for each group of students:

  • graduated cylinder
  • beakers 100ml and 2x250ml (or jars that same size)
  • liquid dishwashing detergent (clear solution works better than cloudy)
  • 1/2 of a banana
  • knife
  • mortar and pestle
  • salt
  • coffee filter
  • rubber band
  • test tube
  • COLD 95% ethanol (this is something that you can't substitute)
  • wooden splint
  • refrigerator

Proceedure:

  • Make a 10% solution of dishwashing detergent in one of your 250ml beakers (make enough to fill the mortar half way)
  • Slice the banana into the mortar
  • Add the 10% detergent solution to cover the fruit
  • Add a pinch of salt
  • Grind the banana in the soap solution until there are no lumps (this is the hardest part, have the students take turns)
  • Fasten a coffee filter to the 250 ml beaker with a rubber band so there is room for the fruit to be poured into the filter
  • Pour the fruit and soap mixture into the filter and place in a cold place to filter
  • Clean up your lab area while you are waiting for the filtering to complete
  • Remove the filter and throw away the contents
  • Pour enough of the liquid into a test tube to fill it 2 cm high
  • Add twice the volume of 95% ethanol (try to layer the alcohol on top by gently pouring it down the side of the test tube)
  • The DNA will precipitate in the boundary between the alcohol and the banana mixture as a cloudy mass
  • Spool the DNA onto your wooden splint

Some additional protocols for DNA extractions:
How to Extract DNA from Anything Living - This site has a great explanation for each step along with pictures!
DNA Extraction: Virtual Lab - This site shows how to extract DNA from human cells.
DNA Extraction from Wheat Germ - This site has a method that never fails to give you a large amount of DNA