Lab 2: DNA Extraction

Introduction
DNA contains the instructions for making you. How you look, what blood type you have, even your tendency to get some diseases. It is found inside the nucleus in just about every single cell of your body. In this lab, you'll break away the membrane around the cell and its nucleus so that you can see your very own DNA.
Materials
• 2 teaspoons (10 ml) 0.9 percent salt water (2 teaspoons table salt in one quart/liter of water)
• disposable plastic cup
• large test tube (or any clear tube that can be sealed with a rubber or cork stopper)
• 1 teaspoon (5 ml) 25 percent mild detergent or dishwashing soap, e.g., Woolite or Palmolive (1 volume detergent or soap + 3 volumes water) (the lab will work without this step, but you will get less DNA)
• 2 teaspoons (10 ml) 95 percent ethanol, chilled on ice
• small test tube
Procedure
1. This procedure will collect some of the buccal cells that line the inside of your mouth. Your cheeks are continuously sloughing off these cells. Swish 2 teaspoons (10 ml) 0.9 percent salt water in your mouth for 30 seconds. This amount of swishing will actually become quite laborious -- hang in there!
2. Spit the water into your cup. Pour this into a large test tube containing 1 teaspoon (5 ml) 25 percent liquid detergent.
3. Cap tube and gently rock it on its side for 2-3 minutes. The detergent will break open the cell membrane to release the DNA into the soap solution. Do not be too vigorous while mixing! DNA is a very long molecule. Physical abuse can break it into smaller fragments, a process known as shearing.
4. Open and slightly tilt the tube and pour 1 teaspoon (5 ml) of the chilled 95 percent ethanol down the side of the tube so that it forms a layer on the top of your soapy solution.
5. Allow tube to stand for 1 minute.
6. Place a thin acrylic or glass rod into the tube.
7. Twirl the rod in one direction to wind the DNA strands onto the rod. Be careful to minimize mixing of the ethanol and soapy layers. If too much shearing has occurred, the DNA fragments may be too short to wind up, and they may form clumps instead. You can try to scrape these out with the rod.
8. After you have wrapped as much DNA onto the rod as you can, remove the rod and scrape/shake the DNA into a small tube containing the rest of the 95 percent ethanol. Your DNA should stay solid in this solution.
9. Show your teacher your DNA if you want credit for the lab!

Questions
1. What was the purpose of the detergent?

2. Was the DNA you extracted from one cell or from many cells?

3. Describe the appearance of the DNA.

4. Why is it important that scientists can extract DNA from cells?