DNA Extraction Activity

DNA Extraction Activity

PSI Biology Name______

Purpose

Students will learn how to extract DNA from their own cheek cells.

Materials

Each student will perform DNA extraction on their own cells; therefore each student needs:

1 1 oz. plastic cup containing 2 ml of a sports drink

1 15 ml tube

1 Plastic Pipet (To transfer your DNA into a microcentrifuge tube if you want to save it)

1 Microcentrifuge tube (see above)

About 2.5 ft of string (To tie around your microcentrifuge tube to make a necklace out of your DNA)

Supplies needed for the class:

www.njctl.org PSI Biology Large Biological Molecules

3 ml graduated plastic pipets

1 bottle of a Sports Drink

Liquid soap (dishwashing detergent works fine)

70% Ethanol

Bucket of ice or freezer for chilling ethanol

Scissors for cutting string (optional)

Marker of labels for 15 ml tubes

Test tube racks

www.njctl.org PSI Biology Large Biological Molecules

Procedure

1. Obtain a 15 ml tube and label it with your name.

2. Pour 2 ml of sports drink into your 1 oz. plastic cup.

3. Put the sports drink into your mouth but DO NOT SWALLOW IT. Swish the sports drink around in your mouth for 1 minute.

4. Spit the sports drink back into your plastic cup. This will contain your cheek cells.

5. Pour the contents of your plastic cup into your 15 ml tube and discard the cup.

6. Place your 15 ml tube into a test-tube rack and let it sit undisturbed for 5-10 minutes. You will see your cells settle to the bottom of the tube.

7. Using a plastic pipet, add about 2 ml of liquid soap to the contents of your 15 ml tube.

8. Cover the top of your 15 ml tube tightly with your thumb and invert it 5 times. DO NOT SHAKE OR STIR IT. This will mix your cheek cells and the liquid soap. The soap acts as a cell lysis solution. It will break open the plasma and nuclear membrane of your cells freeing your DNA so that you can collect it. Place the 15 ml tube back in the test tube rack and let it sit for 2 minutes.

9. Holding your tube at an angle, use a plastic pipet to carefully add cold ethanol to the contents of your tube. Add the ethanol down the side of the tube as you keep it at an angle. You should add ethanol until the total volume of your tube is about 12-13 ml. If you are using a graduated tube, you can see this by the markings on the side of the tube. You should have two distinct layers. DO NOT MIX THE TWO LAYERS.

10. Put your tube back into the test tube rack and let it sit undisturbed for about 10 minutes. You should see wispy strands of DNA beginning to clump together where the two layers meet. The DNA will look like a cobweb extending up from the bottom layer. This will continue to happen as the DNA precipitates out of solution into the ethanol layer on top. The amount of DNA that actually precipitates out will usually vary from person to person.

The following steps are optional:

11. If you want to proudly show off your DNA, you can save it in a microcentrifuge tube and make a necklace out of it. Take a piece of string and make a loop big enough to fit over your head. Tie a knot between the two ends.

12. Using your plastic pipet, transfer your precipitated DNA from the 15 ml tube into the microcentrifuge tube. Do not put the pipe down into the second layer but collect the DNA from the top ethanol layer. You do not have to collect all of the DNA.

13. Once you have transferred the DNA into the microcentrifuge tube, add some ethanol to top it off but do not overfill. You can use the ethanol from your 15 ml tube.

14. With the microcentrifuge tube open, place the loop of your string around the hinge of the cap and close the cap. You are now ready to wear your DNA!

Analysis

1. What type of large biological molecule is DNA? What are its major components?

2. Describe the structure of a DNA molecule.

3. You will notice that the DNA strands you have extracted from your cells appear very long. They are much easier for us to see than RNA strands. What other differences exist between RNA and DNA?

4. One strand of DNA has the following bases: ATTCCGCCTGATGGA. What would the other (complementary) strand look like?

5. What are some things a scientist can do with extracted DNA from any organism?

Teacher notes:

Pre-Lab Prep:

1. Chill the 70% ethanol by storing it in a freezer or in a bucket of ice before the lab.

2. Obtain some embroidery string and cut it into lengths of 2.5 ft. per student

3. Set up a solution station that includes the liquid soap and the ethanol along with plastic pipets.