Mathematics/Physics

DNA Extraction with Kitchen Chemistry

Objective(s):

Students will learn that you can extract DNA from various foods that are found in your refrigerator. This lesson is designed for middle school grades.

Materials Needed:

Dry split peas, Blender (optional), Dish detergent, Toothpicks, Meat tenderizer, Small Glass Containers, Alcohol, Onions, Yeast, Brocolli, Raw chicken liver, Strainer

Strategy:

Students will follow these procedures for DNA Extraction:

Step 1.      

1. Measure out 1 cup of water, ¼ cup of peas, and ¼ tsp. of salt. Stir until salt is dissolved. Leave the peas in water until softened. (I would soak the peas overnight to soften them.)
2. Put the peas and the salt water in the blender and chop for just a couple seconds. You may use a fork to squash the peas. The mixture should be lumpy, containing small pieces of peas. Too much blending will break up the DNA and make it too hard to see.
3. Gently mix the peas and water from the blender with a few drops of soap in a new container.

Step 2.      

1. Put the pea mixture in the strainer.
2. Filter about 1/3 cup of the liquid into a small glass container.
3. Wet the end of a toothpick and dip it into the meat tenderizer.
4. Put the end with the enzymes in the cell mixture and gently stir.

Step 3.       

1. Slowly pour in an equal amount of alcohol (about 1/3 cup)
2. The alcohol will form a layer on top of the cell debris.
3. Watch carefully as the DNA precipitates through the alcohol. The DNA is clear. Small bubbles will attach to the strands as they migrate up through the alcohol. Use the toothpick to gently stir the alcohol layer. Notice how those strands move like snot. The snotty substance is the DNA.

Performance Assessment:

Now that you have extracted DNA from peas, think about each step of the procedure and why it works.

How did each of the ingredients in the demonstration help extract DNA from the other parts of the cell?

What part of cells would be most affected by soap?

What is it in meat tenderizer that breaks down meat?

Alcohol and salt: Why does only the DNA, and not the other parts of the cell, rise to the top after addition of alcohol?

References:

DNA Extraction with Kitchen Chemistry. The Natural History of Genes. University of Utah, Salt Lake City, UT