DNA contains messages that the body reads like an instruction book. If you were to unwind one strand of DNA in your body (there are several million), it would stretch more than 5 feet but would be so narrow that you couldn't see it.

The basic chemical unit in a nucleic acid is a nucleotide. A nucleotide in DNA consists of one of four nitrogenous bases linked to deoxyribose, which is in turn linked to a phosphate.

All living things contain DNA. The exception to this is bacteria; it is the only living organism known to lack DNA.

You will be making an aqueous solution in this experiment. From it you will find and extract the DNA. An aqueous solution is one in which water is the solvent.

Also important to this experiment are the concepts of polar and nonpolar molecules. A polar molecule is a molecule in which the electric charge is not distributed evenly over the molecule. Because the molecule is polar, one side of it has a slight negative charge where the other side has a slight positive charge. Of course, a nonpolar molecule is a molecule whose electric charge is evenly balanced from one end of the molecule to the other.

DNA, for example, is a polar compound, because it contains many negative charges due to the phosphates in the sugar-phosphate backbone of each DNA strand.

In this experiment you will use sand. The sand is used to soften and break apart the membranes of the onion. You will also use detergent in this experiment. The detergent is used to break apart the proteins in the membranes and to break apart the cell walls of the onions. Onions are plants, so they have cell walls instead of the cell membranes you find in animal cells. Finally, the salt you use in this experiment is very useful once the proteins in the membranes have been exposed by the detergent. In effect, the negatively charged DNA is naturally attracted towards the positively charged proteins in the cell membrane. This is a definite problem because our goal is to isolate the DNA. Thus, the salt is added to minimize the attractive forces between the DNA and the proteins by unbalancing the positive and negative charges between them. After this, the DNA is much easier to separate from the rest of the solution.

• 20 grams (5 teaspoons) of diced onions
• 1 teaspoon of sand
• 30 mL of warm water - 1 teaspoon of clear Ivory dish detergent
• 1/2 teaspoon of salt
• 30 mL of 99% ethanol (or 99% isopropyl alcohol) which can be purchased at any pharmacy
• mortar and pestle
• 2 x 100 mL beakers (or similarly-sized glass jars)
• 50 mL graduated cylinder
• 1 glass rod
• 1 20x20 cm sheet of cheesecloth

1. Dice an onion until approximately 5 teaspoons have been obtained.
2. Transfer the diced onions to a mortar and pestle.
3. Add 1 teaspoon of sand and grind vigorously for 3 minutes.
4. Prepare solution A as follows:
   1. Transfer 30 mL of warm water into a 100 mL beaker.
   2. Add 1 teaspoon of detergent and mix well with a glass rod.
   3. Add 1/2 teaspoon of salt and mix until dissolved.
5. Transfer the mush from the mortar into the 100 mL beaker containing Solution A.
6. Using a glass rod, stir the mixture for 5 minutes.
7. Transfer only the liquid to a new 100 mL beaker by filtering the mixture through the cheesecloth. Try to obtain as much of this yellow liquid as possible, as it contains the DNA.
8. Measure 30 mL of the 99% ethanol or isopropyl alcohol into a graduated cylinder.

9. Using a glass rod as a guide, add the alcohol very slowly to the beaker containing the yellow liquid. If this is done correctly, you should observe two separate phases.
10. Insert the glass rod into the centre of the solution until it just penetrates the lower phase.
11. Turn the rod in wide circles (always in the same direction). The crude DNA will begin to form a solid (called a precipitate). The solid will be long filaments which stick to the glass rod.
12. When the two phases are completely mixed (they are said to be homogenous), touch the bottom of the beaker and rotate the rod (turn the rod on itself). This will cause the DNA to wrap tightly around the rod.
13. Once a sufficiently large mass of DNA has been obtained, remove it form the glass rod and admire your product.

DNA is important in several other branches of science, such as genetic engineering.