Extracting DNA at Home
Laboratory Investigation

  • to become aware of several simple protocols that may be used to isolate DNA from live materials
  • to recognize what type of problems are associated with this technique
  • Introduction

    All living cells, eukaryotic or prokaryotic, contain DNA. It is the genetic code of DNA, written in the sequencing of its nitrogen bases, that determines the unique characteristics of an organism. It also tells us something about the relatedness of all organisms. The last few decades have seen advances in genetic research which have included the use of recombinant DNA in the advancement of medicine for both diagnosis and treatment. The first step in genetic analysis or use is the extraction of the DNA. The procedure can now be done at home at your kitchen sink and table. There are a number of techniques that are listed below including an article from Scientific American. Use one of the protocols listed and extract DNA from one of the types of cells mentioned. Remember that this represents a first crude step prior to more refinement and analysis for further use.

    Arizona's version of kitchen sink extraction of DNA.

    A marvelous sequence on how to extract DNA from wheat germ. Just follow the instructions at the bottom of the first page.

    Scientific American, September 1998, "Spooling the Stuff of Life"
    by Shawn Carlson

    Some of the basic information from the Scientific American article is abstracted below.

    DNA is a large molecule containing millions of atoms. DNA typically breaks up into numerous fragments with a slight negative electric charge. Sodium ions from table salt are attracted to the negative charges on DNA. This neutralization prevents the separate fragments of DNA from sticking to one each other. By regulating the salt concentration, DNA fragments will either disperse or stick together.

    To be successful, the procedure requires that the cell be broken apart. Its nuclear material must be set free and separated from associated proteins. If removing DNA from a plant cell, the cell wall must also be broken down.

    One technique is as follows. "You'll first need to prepare a buffer. Pour 120 milliliters (about four ounces) of water into a clean glass container along with 1.5 grams (1/4 teaspoon) of table salt, five grams (one teaspoon) of baking soda and five milliliters (one teaspoon) of shampoo or liquid laundry detergent. These cleaners work well because they have fewer additives than hand soaps--although do feel free to try other products as well." (Dawn detergent is the best of the bunch.)

    "The detergent actually does double duty. It breaks down cell walls and helps to fracture large proteins so they don't come out with the DNA. In any case, try to avoid using tap water."(You can purchase distilled water in the grocery or pharmacy.) "To slow the rate at which the DNA degrades, it's best to chill the buffer in a bath of crushed ice and water before proceeding."

    Almost any cell material will provide decent results. "I got great results with an onion, and the folks at Edvotek also recommend garlic, bananas and tomatoes. Dice it and put the material into a blender, then add a little water and mix things well by pulsing the blades in 10-second bursts. Or, even simpler, just pass the pieces through a garlic press. These treatments will break apart some of the cells right away and expose many cell walls to attack by the detergent."

    "Place five milliliters" (one teaspoon)"of the minced vegetable mush into a clean container and mix in 10 milliliters of your chilled buffer. Stir vigorously for at least two minutes. Next you'll want to separate the visible plant matter from the molecule-laden soup. If you do not have a centrifuge, strain the material through an ordinary coffee filter to remove most of the plant refuse. With luck, any stuff that leaks through should either sink or float on top, so it will be a simple matter to pour off any solids into the sink and then pour the clear liquid into a clean vessel" such as a shot glass or plastic cup.

    "The solution now contains DNA fragments as well as a host of other molecular gunk. To extract the DNA, you will need to chill some isopropyl alcohol in your freezer until it is ice-cold. Most drugstores sell concentrations between 70 and 99 percent. Get the highest concentration (without colorings or fragrances) you can find. Using a drinking straw, carefully deposit 10 milliliters of the chilled alcohol on top of the DNA solution. To avoid getting alcohol in your mouth, just dip the straw into the bottle of alcohol and pinch off the top. Allow the alcohol to stream slowly down along the inside of the vessel by tilting it slightly. The alcohol, being less dense than the buffer, will float on top. Gently insert a narrow rod through the layer of alcohol. Gingerly twirl back and forth with the tip of the stick suspended just below the boundary between the alcohol and the buffer solution. Longer pieces of DNA will then spool onto the stick, leaving smaller molecules behind. After a minute of twirling, pull the stirrer up through the alcohol, which will make the DNA adhere to the end of the stick and appear as a transparent viscous sludge clinging to the tip." (DNA will appear as a mucus-like plug [snotty appearance] or short stringy strands of whitish material)

    "Although these results are impressive, this simple and inexpensive procedure does not yield a pure product. Professionals add enzymes that tear apart the RNA molecules to make sure they do not get mixed up with the coveted DNA."

    Exciting as it may be, extracting an organism's DNA is only the first step in most biological experiments.

    Pictures of the process and outputs are nicely shown at this site.

    Additional Reference Sites

    Excellent background information source.