NOTE: Exercise 2 will only be conducted by Natsci2 students while Natsci2A will conduct exercises 2 and 3
Exercise2: DNA EXTRACTION
PROCEDURE
1. In the first container, mix 30 ml of water with 1 tbsp of salt.
2. In the 2nd container, mix 15 ml (3 tbsp) of water and 5 ml (1 tbsp) of liquid dishwashing soap.
3. Take 2 ml of the salt water solution from the first container and swirl it in your mouth for 30 seconds.
4. Spit the salt water and whatever contents are moving around in your mouth into the 3rd container.
5. Transfer about 1 ml of the spit into a test tube.
6. Add 1 ml (1 tsp) of the soap solution to the test tube and mix by gentle swirling for 1 min
7. After swirling, pour 15 mL (3 tbsp) of alcohol gently to the side of the test tube without mixing so that it floats.
8. After 1 minute, a cloud of bubbles will be seen at the bottom of the layer of alcohol and attached to it are transparent to whitish strands and that it is your DNA.
9. Remove your DNA and place it on a slide. Examine under a microscope. How does it look like?
QUESTIONS
1. Why should the alcohol be cooled first before using it the experiment?
2. Why do we need to use salt solution for swirling? Can’t we use other just plain water?
3. What is the purpose of the soap solution? How does the soap solution able to do it?
4. Is your DNA as seen in microscope the same as the theoretical double-stranded helix coil? Why?
EXERCISE 3. BACTERIAL STAINING
PROCEDURE
1. Swipe a toothpick in your cheek cells. Use another toothpick for your tongue and in between your finger toes.
2. Apply the swiped toothpick into the slide, air dry for 60 seconds.
3. Apply crystal violet. Wait for 60 seconds then rinse completely with water. Be sure that the bacteria is stained otherwise you have to repeat step 1 to 3.
4. Add gram’s iodine, then wait for 60 seconds.
5. Rinse completely with water.
6. Add safranin and wait for 45 seconds
7. Then rinse and dry over heat.
8. View the slide under microscope.
QUESTIONS
1. What is the color of gram-positive bacteria? How doest it differ with the color of gram-negative?
2. Why are the colors of the two bacteria different? How did it happen?
3. What is the purpose of the gram iodine?
4. Why do we need to dry the slide over a heat rather than just simply air-drying?
