Petra M. Frey

Vegetables, fruits, cereals and meat — all plant and animal products — contain DNA in various amounts. DNA, the carrier of genetic information, the recipes or blueprints of an organism, is made up of four different chemical units. These can be digested and used just like any other nutrient in our food. A pound of broccoli, for example, contains about a tenth of an ounce DNA.

Usually DNA is degraded during cooking, but even if DNA is eaten uncooked, like in the case of apples, a tomato, or a salad, the DNA is degraded rapidly in our stomach. Eating DNA should not be a concern: even mother’s milk contains high amounts of DNA, because newborns have a higher need for them.

In this experiment we will isolate the DNA of a piece of tomato to see what DNA actually looks like. It will also give us an idea of the amount of DNA we eat and of some of its physical properties.

Protocol

1. Chop one quarter of a tomato into very fine pieces. Mix 2 table spoons of extraction buffer^*) with 1/2 teaspoon of dishwashing detergent (or DIAL, liquid soap) in a glass. Add the chopped tomato and grind for 1 minute to a fine slurry.
2. Strain the well-blended tomato through a washcloth or two layers of paper tissue.
3. Pour 1/2 tablespoon of strained mixture in a small, clear glass. (A liquor glass works well.) We will use plastic tubes.
4. Add 1/2 table spoon of water to the clear tomato mixture.
5. Carefully add 4 table spoons of cold alcohol (95% ethanol). The alcohol should float on top of the tomato mixture, but don’t worry if it mixes a bit.
6. At the layer between the tomato juice and alcohol you will see a whitish, "snotty-looking", substance. This is DNA. Carefully swirl the two solutions in the glass, to get more DNA. Make a small hook with a paper clip and reach in to hook the stringy DNA and pull it out.

Congratulations, you're now on your way to becoming a genetic engineer!

 

*)Extraction buffer

in 1 liter of distilled water mix:

8.8 g Sodium chloride

44 g Sodium citrate