DNA Extraction Lab Demonstration DNA contains the instructions

DNA Extraction Lab

• Demonstration

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 activity, you'll break away the membrane around your own cheek cells and its nucleus so that you can see your very own DNA.

DNA is only about 50 trillionths of an inch long. The reason it can be seen in this activity is because students are releasing DNA from a number of cells. This happens when the detergent or dishwashing liquid breaks, or lyses, the membranes around the cell and around the nucleus.

Once released, the DNA from the broken open cells intertwines with DNA released from other cells. Eventually, enough DNA intertwines to become visible to the eye as whitish strands. One strand of DNA is so thin (. 0000002 mm) one would never be able to see it without using a microscope.

Detergents break open cells by destroying the fatty membrane that encloses them. This releases the cell contents, including DNA, into the solution. Detergents also help strip away proteins that may be associated with the DNA.

DNA is not soluble at high ethanol concentrations, so it precipitates out as long strands. Salts, such as sodium chloride, also greatly aid in precipitating DNA. The ethanol also causes gases dissolved in the water to be released, which may be observed as small bubbles. This procedure may not work well if a person has eaten corn flakes for breakfast. Presumably this is because the corn flakes have scoured too many buccal cells from the inside of the mouth. Repeating may give low yields if most of the loose buccal cells have already been harvested

Materials 1. Salt water mixture (2 approx teaspoons table salt in one quart/liter of water) 2. “Squirt” water bottle (to squirt salt water into your mouth. ) 3. large test tube (or any clear tube that can be sealed with a rubber or cork stopper. ) 4. 1 teaspoon (5 ml) 25 percent mild detergent or dishwashing soap. 5. 2 teaspoons (10 ml) 95 percent ethanol, chilled on ice 6. small clear tube with seal

Procedure 1. To collect buccal (cheek) cells that line the inside of your mouth which are continuously being sloughed off by your cheeks. Swill 2 teaspoons (10 ml) 0. 9 percent salt water in your mouth for 30 seconds. 2. Spit the water into your test tube which should already contain 1 teaspoon (5 ml) 25% 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) fluid ounces of the chilled 95% ethanol down the side of the tube so that it forms a layer on the top of your soapy solution. Allow tube to stand for 1 minute. 5. Place a thin acrylic or glass rod into the tube. 6. Stir or 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. 7. 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.

Top of alcohol layer Bubble DNA

Large clump of DNA

DNA looks the same no matter what the source because the bases are always the same: A, T C and G

Lab tech spooling DNA

If desired place a glass or acrylic rod into the test tube and twirl to collect the DNA. Do not put the rod below the alcohol layer. Twirl or spool the DNA to place into a test tube with alcohol only.

• Now answer the questions on your half worksheet. • You can save your DNA, or throw it out your choice