(idea) by thyme Sat Apr 13 2002 at 21:41:15
Extraction of DNA from Wheat Germ

This easily performed procedure produces large amounts of DNA. This DNA is, sadly, pretty crappy: impure and damaged. In short, you won't be making hamsters with wheat for fur or cloning wheat anytime soon using the DNA you get from this procedure. You probably will be surprised by what the DNA looks like (a bit like semen, actually), and by how much you can get from a little bit of wheat germ.

Enjoy, and remember: "Today is a good day for science!"

Materials

Reagents:

Tap water and distilled water
Raw (untoasted) wheat germ - 1 gram, or approx. 1 tsp.
Liquid detergent (palmolive, dawn) - 1.5 mL
Meat tenderizer (Adolph's, unseasoned) - 1 gram, or approx. 1 tsp.
Ethyl alcohol - 10mL iced and 20 mL room temp.
Water bath at 55° C
Sodium bicarbonate (NaHCO3) (baking soda) 1M solution1 - 2.5 mL

Apparatus:

Celsius thermometer
1 100 mL beaker (or a similarily sized Pyrex container)
2 50 mL beakers (not heated, so any similarly sized container can be used)
1 250 mL beaker (for hot water bath- similarily sized Pyrex container can be used)
Ice bath
10 mL graduated cylinder
Stirring rod
Hot plate

Procedures

  1. Make a hot water bath by filling the 250 mL beaker 1/3 full of tap water and heating it on a hot plate to 55° C. Do not allow temperature to exceed 60° C. If you don't have a hot plate, water out of your tap may get hot enough to work, just make sure you keep replenishing it to keep the temperature within the correct range.
  2. Measure 25 mL of distilled water into a 100 mL beaker. Place this in the hot water bath. Mix in 1 gram of wheat germ and stir utill it has partially dissolved. Gently stir in 1.5 mL of detergent and heat for five minutes. (Try not to create many bubbles in the solution as you stir it.)
  3. After five minutes, gently stir in 1 gram of meat tenderizer and 2.5 ml of the sodium bicarbonate solution (or a pinch of baking soda). Let this mixture sit at 55° C for fifteen minutes.
  4. Transfer the beaker containing the wheat germ mixture to an ice water bath. Cool it to room temperature (21-23° C). Stir gently during the cooling.
  5. Keep the beaker in the ice water bath. Place the stirring rod into the beaker of wheat germ, the carefully pour 10 mL of ice-cold ethyl alcohol down the rod (if you don't have a stirring rod, carefully tilting the container and pouring down the side of it works too). You want to form an undisturbed layer of ethyl alcohol over the wheat germ mixture. Allow this to stand undisturbed for two to three minutes.
  6. There will be a visible interface between the wheat germ mixture and the ethyl alcohol. A fibrous, white precipitate should begin to appear at the interface- DNA! Use a flat toothpick to carefully spool the DNA. Be careful not to mix the ethyl alcohol and wheat germ mixture, as the DNA might dissolve.
  7. Transfer the DNA into a beaker containing 10 mL of room temperature ethyl alcohol. The DNA can be washed by swirling it around gently and transferring it to another beaker of room temperature ethyl alcohol.
  8. What you want to do with your (impure, damaged, crappy) DNA now is up to you... you could prove that it's DNA, look at it under a microscope (though you won't see any double helix formations using regular microscopes), etc.

How it works

Detergents solubilize and break down the lipids and proteins that form the cell and organelle membranes of the wheat germ. They also disrupt the bonds holding membranes together. The cell contents, including the nucleus and organelles, are released. Heat softens the cell wall and membranes and enhances the action of the detergent. Heat also denatures enzymes (particularly DNase) that would otherwise fragment the DNA. The temperature should not be raised above 60° C because higher temperatures denature the DNA and make spooling impossible. Eventually, even at 55° C, the DNA would break down, which is why the mixture is cooled.

The sodium bicarbonate is used to maintain a pH of about 8. At this point, the DNA is most stable, and the enzyme in meat tenderizer is most effective. The meat tenderizer contains the proteolytic (protein breaking) enzyme papain, which is found in papaya, pineapple, and other fruits. The papain completes the breakdown of proteins that might precipitate in alcohol, and completes the breakdown of nuclear membranes to release DNA.

DNA is soluble in water, but not in alcohol. Where the two layers meet, the DNA becomes dehydrated, precipitating out of solution. This seems to work best with ice-cold ethyl alcohol.

1 A 1M solution of baking soda would be 1 mole of NaHCO3 per liter of water. If you can't get such a solution, just put a pinch of baking soda in 2.5 mL of water and use that. It should work just fine.


This lab procedure paraphrased from an un-copyrighted worksheet handed out in my high-school biology class. Mad props to science teachers worldwide!

I like it! 1 C!