Embedded Files
DNA possesses the information that determines an organism's characteristics and is transmitted from one eneration to the next. The length of DNA in a cell is about 100,000 times as long as the cell. However, DNA fits into the nucleus, which takes up only about 10% of the cell's volume. This is because the DNA is specially packaged. The basic structure of DNA is that of a twisted ladder called a double helix. To shorten the DNA molecule it wraps around the proteins, folds back on itself, and coils into a compact chromosome. Humans have 46 chromosomes in the nucleus of almost every cell. Individual chromosomes can be studied using a microscope, but the double helix of a chromosome is so thin, it can only be detected by innovative, high-tech procedures. Chromosomal DNA is not visible to the naked eye, but when chromosomal DNA is extracted from multiple cells, the amassed quantity can be easily seen, and looks like translucent strands of mucous-like cotton. In this activity, you will isolate your own chromosomal DNA from a large quantity of cheek cells and fashion the DNA into the centerpiece of a wearable pendant necklace.
Materials
Introduction
Gatorade
Small plastic measuring cup
Thread
Ethanol 70%
Cell Lysis Solution
15 milliliter tube
Plastic Pipet
Pendant tube
Procedure
1. Using a marker or label, write your name or initials on your 15 milliliter tube.
2. Take 2 milliliters of Gatorade into your mouth and swish it around your mouth for 1 minute. Do not swallow the Gatorade. While you swish, gently and continuously scrape the insides of your cheeks with your teeth to help release the cheek cells.
3. After 1 minute of swishing, spit the sports drink with collected cheek cells back into the small plastic cup.
4. Carefully pour the contents of the small plastic cup into your labeled 15 milliliter tube. Discard the cup.
5. (This is an optional step and will not affect the results of the procedure. You may skip ahead to step 6.)
If time allows, you can watch your collected cheek cells settle as a pellet in the bottom of your 15 milliliter tube. Place your tube upright and let it stand undisturbed. After 5-10 minutes, you will begin to see the cells collect in the bottom of the tube. (Most cells will settle before 30 minutes.) Hold the tube up to light to better see the cells. Some samples will pellet more tightly and quickly than others, and some will have a higher percentage of cells than others. This variation is a normal outcome.
6. Use a graduated pipet to add 2 milliliters of cell lysis solution to your collected cheek cells.
7. Cap your 15 milliliter tube tightly and invert it five times. Allow the tube to stand for 2 minutes.
8. Hold the 15 milliliter tube at an angle and, using the plastic pipet, carefully add cold 70% ethanol by running it down the inside of the tube. Add the ethanol until the total volume of the liquid reaches 12-13 milliliters. You should have 2 distinct layers. Do not mix the 2 layers.
9. Wispy strands of translucent DNA will begin to clump together where the two layers meet. It will look like a cobweb extending from the lysed cheek cell layer. Tiny bubbles will appear where the DNA precipitates.
10. Place your 15 milliliter tube upright in a test tube rack or a beaker and let it stand undisturbed for a minimum of 10 minutes. During this time the DNA will continue to precipitate out of solution and extend like a ribbon through the ethanol layer. DNA from different samples will differ and not all DNA samples will extend through the entire ethanol layer.
11. Tie the ends of your thread together with a knotto form a loop. Make sure the loop can fit over yout head, since this will become your knecklace.
12. Use your plastic pipet to transfer your precipitated DNA out of the 15 ml. tube and into the pendant tube. Begin pipetting the DNA from the end of the most extended strand in the ethanol layer. As you pipet, the DNA will be drawn together. Do not move your pipet tip down into the cell lysate layer. If some of the DNA remains attached to the cell lysate layer, draw the pipet up until the DNA in your pipet detaches from that in the cell lysate layer. You do not need to transfer the entire precipitated DNA into the pendant tube. Before you expel the DNA into the pendant tube, allow it to sink to the tip of the pipet. If the DNA does not sink, release the ethanol into the 15 ml tube drop-wise until the DNA is in the pipet tip. Expel the DNA into the pendant tube and fill the remaining space drop-wise with the ethanol. Do not overfill.
13. With the pendant tube open, place the loop of thread around the cap hinge. Vlose the cap and put on your DNA necklace. Invert the pendant tube to see your DNA move throught the ethanol.
Scientific Principle
DNA is extracted through a cell lysis solution. Cell lysis is when the cell is broken open.
Safety Regulations
1. Each person should only work with his or her own cheek cells. Once the cells have been collected and transferred to the 15 milliliter tube, the collection cups should be discarded.
2. Do not ingest an of the solutions or the extracted DNA.
3. Ethanol is a flammable alcohol that must be kept away from heat and flames at all times. Remember that your pendant necklace will also contain small amounts of ethanol.
4. Ethanol is harmful if inhaled or swallowed. It may cause irritation to your eyes, skin, and respiratory tract. If swallowed it may cause gastrointestinal discomfort.
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