Wheat germ, kiwi fruit and onion DNA extractions all work well. The wheat germ method is simple, you get lots of DNA, and it isn’t smelly.
Test the detergent, as only some brands promote the production of DNA.
There are two web sites recommended for DNA extraction pracs:
1. http://gslc.genetics.utah.edu/units/activities/ This site has an excellent wheat germ DNA extraction which I have used before. It is easy and you get lots of DNA.
All the ingredients can be bought at the supermarket. You can use rubbing alcohol instead of ethanol and it still works fine. The detail is good and easy to follow and there are a number of different DNA extractions you can try.
EXTRACTION OF DNA FROM WHEAT GERM
From Jan McGaw, Ferny Grove State High School, Queensland
Raw wheat germ
Detergent (Dawn Lemon Zest works well)
Glass hook, paper clip or pop stick
50 or 100ml beaker
2x 50 ml measuring cylinder
1. Place 1g or 1 level teaspoon raw wheat germ in a 50 or 100ml beaker
2. Add 20 ml of hot (50-60 degrees C) tap water and mix constantly for 3 minutes.
3. Add 1 ml of detergent and mix gently every minute for 5 minutes. Avoid creating foam.
4. Remove any foam with a pipette or paper towel.
5. Tilt the beaker and SLOWLY pour 14ml of methylated spirits down the side so that it forms a layer on top of the mixture. Do not mix the 2 layers together. DNA forms at the water-meths boundary. It is crucial to pour the meths very slowly so that the DNA forms in a layer on top of the water. If the meths mixes with the water, it will become too dilute and the DNA will not precipitate.
6. Let it sit for a few minutes. White, stringy DNA will begin to appear. After a while the DNA will float upwards. Use a glass hook, paper clip or pop stick to collect the DNA.
7. If you want to keep the DNA, store it in 50-70% ethanol in a sealed tube, or air dry it on a paper towel.
KIWI FRUIT METHOD 1:
Small ziplock plastic bag (15 x 9 cm)
Extraction solution (50ml shampoo, 7.5g salt and water to final volume 500mL.) enough for 25 students and don’t use baby shampoo or one that contains conditioners. Try Pear’s shampoo.
Small test tubes
Cheesecloth or gauze or Chux
Iced water bath
95% ethanol or isopropanol (rubbing alcohol)
Cutting board & knife
1. Cut half of one kiwi fruit into six pieces and place in ziplock bag
2. Add 20mL of extraction solution
3. Close bag, carefully removing as much air as possible
4. Press kiwi fruit and extraction solution together for five minutes
5. Using iced water bath, alternate cooling the mixture for one minute and continue to press the contents together for one minute. Repeat three times
6. Use the cheesecloth/gauze/Chux in a funnel to filter the mixture (all groups can filter through the one funnel)
7. Each person gets about 2mL of cold ethanol. DO NOT shake the tube.
8. DNA strands should form at the top of the tube and can be removed using glass rod or paper clip
KIWI FRUIT METHOD 2
Plastic Petri Dishes
¼ very ripe Kiwi Fruit
Filter paper (with a fast filter speed such as a Whatmans no. 4)
Large test tube
Test tube rack
Ice cold methylated Spirits
Pipette or dropper
25 ml measuring cylinder
25 ml of salt and detergent solution:
salt: 3g/100ml water
and washing-up detergent:10ml /100ml water
(This is best made up as a bulk solution for each group to collect 25 ml).
1.Using the plastic knives chop up the kiwi fruit into small pieces and place in 100 ml beaker with 25 ml of the salt and detergent solution.
2.Sit in a water bath for 15 minutes at 60 degrees Celsius.
3.Pour contents into a filter paper in the filter funnel.
4.Collect the filtrate in a large test tube.
5.Discard the filter paper and kiwi fruit pulp.
6.Carefully drizzle the ice-cold methylated spirits down the side of the test tube so that it forms a purple layer on top of the green layer. Let the test tube sit in the test tube rack.
7.You should almost immediately see a white layer beginning to form at the boundary between the green and purple layer. This is the DNA.
8.Use a wire loop to hook out some of the DNA.
EXTRACTION OF DNA FROM ONION
Chux cloth or similar
Protease enzyme or meat tenderiser powder from supermarket
Collect only when needed: ice, 5ml cold ethanol, disposable pipette, glass hook.
1. Chop onion into really small pieces.
2. Add chopped onion to blender with 100ml hot tap water
3. Blend for 10-15 seconds.
4. Put the blended onion into a 250ml beaker.
Add 1 teaspoon Lux flakes and 2g sodium chloride and stir well.
How does blending help to extract the DNA?
5. Boil for 5 minutes, stirring gently.
While the mixture boils, read the following:
The Lux flakes cause the cell membrane to break down and emulsify the lipids and proteins of the cell by disrupting the polar interactions that hold the cell membrane together. The soap flakes form complexes with these lipids and proteins, causing them to precipitate out of solution. Sodium chloride enables the nucleic acids to precipitate out of an alcohol solution because it shields the negative phosphate end of DNA, causing them to come close together and coalesce.
The heat treatment softens the phospholipids in the cell membrane and denatures the DNA-ase enzymes, which, if present, would cut the DNA into small fragments so that it would not spool.
6. Cool the onion mixture to 40 degrees C by stirring gently and running cold tap water over the outside of the beaker for 2 minutes and then placing it in an ice water bath, using the 400ml beaker until 40 degrees is reached.
7. Add 1 level teaspoon of protease enzyme (meat tenderiser) powder and stir gently for 5 minutes.
8. Filter through layers of Chux cloth into a 100ml baker.
9. Put 10ml of the filtrate into a 100ml beaker.
10. Add 10ml of icy cold ethanol to the beaker, pouring it SLOWLY and carefully down the side of the beaker so that the ethanol sits on top of the filtrate. You may find it easier to add the ethanol using a pipette.
11. Let it sit for 2-3 minutes. You should see the DNA precipitate out of solution near the boundary between the onion filtrate and the ethanol. It looks like mucous.
12. Gently swirl the DNA using the glass hook. Swirl so that the hook is in the onion filtrate below the ethanol and gently lift it up through the ethanol. You may have to repeat this several times to accumulate enough DNA.
Congratulations, you are one of the few people to have extracted DNA from the cells of a living organism.