1. Chill a bottle of rubbing alcohol by placing it in a freezer for 10 or more minutes.
2. Peel a ripe banana. Discard the peeling and place the banana in a quart-size resealable plastic bag.
3. To the bag add the following:
1/2 cup of distilled water
1/2 teaspoon of clear dish washing liquid
1/2 teaspoon of table salt.
4. Seal the bag, and then with your hands, gently squeeze the bag until the banana is smashed into a mush.
a. DO make the banana as mushy as possible.
b. DON’T make soap bubbles, so do not shake the bag.
Facts: Smashing the banana breaks cell walls and separates cells. The detergent breaks the fatty cell membrane surrounding each cell as well as the fatty nuclear membrane surrounding the nucleus. The contents of the ruptured cells and ruptured nuclei are part of the mushy banana mixture. The salt helps separate the DNA from the mixture.
5. Line a funnel with two layers of cheese cloth. Stand the funnel in clean jar.
6. Pour the banana mixture into the cloth lined funnel.
Facts: The liquid that passes through the cheese cloth and collects in the test tube is called the filtrate. The solid materials collected by the cheese cloth are called the residue.
7. When the bottom of the jar is covered with about 1/2 inch of filtrate, move the funnel to a second clean jar. The filtrate collected in the second jar can be used if needed.
8. Fill a test tube (or narrow jar) about 1/4 full with the banana filtrate.
9. Add 1/4 test tube of cold rubbing alcohol to the tube containing banana filtrate. (You want equal amounts of filtrate and alcohol.)
a. DO tilt the test tube so that the alcohol runs slowly down the side of the tube. You do not want the alcohol and filtrate to mix together.
10. Stand the test tube upright and periodically for 5 minutes or more observe the area where the top layer of alcohol touches the bottom layer of banana filtrate.
Facts: The DNA precipitates into the alcohol layer. DNA is soluble in water but is not soluble in alcohol. The DNA precipitates in the salty water, which means the DNA comes out of solution. Along the phase boundary (where the two liquids–alcohol and banana filtrate- meet) the DNA appears to grow upward into the alcohol layer. Look for a tiny bubble at or near the phase boundary. Often the bubble rises with strings of DNA seemingly attached to it.
The clumped DNA looks like –well the truth is that it looks like slimy snot.