Wheat Germ DNA Isolation Experiment: Activity
- Where is DNA found?
- How can it be isolated?
- Can it be seen with the naked eye?
- If so, what does it look like?
- Divide into groups of 2-4 people.
- Obtain 2 large test tubes and 3 small test tubes. Label one large tube WG for wheat germ and one C for control. Label one small tube WG, one C and the other P for pure DNA.
- Add about 1/4 gram of wheat germ to the large WG tube. The instructor will demonstrate how to estimate 1/4 gram.
- Fill the large WG and C tubes about half full with hot distilled water and put on the lid. Shake the tubes vigorously for 5 min.
- You will be given a small tube containing a detergent/salt mixture. Add 1/2 of the detergent/salt mixture to the WG tube and the rest to the C tube.
- Gently mix the two large tubes for 3 min. by repeatedly turning them upside down.
- Let the large tubes settle for 2 min. and then use a dropper pipette to transfer some of the liquid from the top of each tube into the corresponding small tube (liquid from the large WG tube into the small WG tube, and so on) until it is about 1/2 full.
- Add the purified DNA solution to the small P tube till it is about 1/2 full.
- Using a dropper pipette, add an equal amount of ice cold rubbing alcohol (i.e. until the tube is full) to each small tube by letting the alcohol gently run down the side of the tube. The alcohol will form a layer on top of the water solution. The DNA cannot dissolve in alcohol, so it becomes a solid (precipitates) right at the dividing line between the two liquids. Use a toothpick to gently stir the liquid in the tubes and watch the DNA begin to precipitate. Use the toothpick to pull up the DNA so that you can see it well.
- After observing the DNA this way, shake up the tubes to mix the two liquids, and let the tube set for a few minutes.
- Use a toothpick to remove the DNA from the tubes and place them on a fresh coffee filter to dry. If the toothpick will not easily pick up the DNA, just pour the whole tube onto the coffee filter and let all of the liquid dry (this way just takes longer to dry).
- Write down anything that you saw happen in the test tubes.
- Write down a description of any product you obtained.
- Answer as many of the following questions as you can. Then, discuss the answers with the whole class.
- Where did the DNA come from?
- Why did we do the C and P tubes?
- Could you see the DNA?
- What did it look like?
- Did the WG tube have more product than the P tube? If so, why?
- How could you get a better look at DNA?