Have you ever heard of deoxyribonucleic acid?
Of course you did! That’s the full name of DNA, the building blocks of genes and chromosomes
Would you like to see DNA? Then go ahead and extract the DNA of a banana!
- Distilled water (available in pharmacies and some groceries, may be labeled as ‘de-mineralized water’)
- 2 clear cups
- Table salt
- Clear shampoo, soap or detergent
- Chilled isopropyl alcohol (rubbing alcohol, available in pharmacies). The cooler, the better.
- Coffee filter
- Clear tube or test tube
- Adult supervision
- Add 1 cup of distilled water to ½ banana in the bowl and mash it. Make sure the banana is well blended.
- Mix 1 teaspoon of shampoo, 2 large pinches of salt and 4 teaspoons of distilled water in a clear cup. Stir gently to avoid bubbles. Continue until the salt is dissolved.
- Add 2 teaspoons the banana mash into the water-salt-shampoo solution. Stir the mixture slowly for 5 minutes.
- Place the coffee filter inside the second cup, be careful not to let the filter touch the bottom of the cup. Pour your mixture into the filter. Allow it to filter for about 10 minutes.
- Gently stir the filtrate from the bottom of the cup and set it aside.
- Add 2 teaspoons of chilled isopropyl alcohol to your test tube. Then, add two teaspoons of your filtrate to the alcohol.
*** Attention ***
Rubbing alcohol is a flammable chemical! Also, it should NOT be swallowed!
- Let this mixture sit about 5 minutes. You will start to see your DNA precipitate gathering at the top.
What’s going on here?
As the DNA lies inside every cell nuclei, we need to break the cells in order to collect it. First, you mashed the banana in order to separate the cells. Then you mixed the mash with the detergent and salt solution because the detergent molecules dissolve the fatty cell membrane (wall) and organelles (a structure protected by a wall within the cell, such as the nuclei). The salt breaks up protein chains around the DNA, making it “available” for us. By that stage you already had the DNA dissolved in the water, but had to get rid of all the pulp form the solution. That’s why you filtered it and collected the dissolved DNA in the filtrate (the stuff that went through the filter). Finally, since DNA is insoluble in cold alcohol, it doesn’t like to be in the alcoholic solution and precipitated (clump together and becomes solid) upon the alcohol addition.