DNA Extraction Lab
Contributed by the Shodor Education Foundation
What does DNA look like? You can see for yourself by isolating large amounts of DNA from yellow onions. This is an easy procedure that you can even do at home.
Materials and Equipment
Per Class
- Blender
- Murphy's Vegetable Oil Soap
- Hot water bath (60 to 70 degrees Celsius)
- Rubbing alcohol
- Salt (non-iodized)
- Chopped yellow onions
Per Group
- Large container of ice
- Funnel
- Two 250ml beakers or comparable containers
- 50ml beaker or comparable container
- Glass stirring rod, plastic stick or toothpick
- Cheesecloth or coffee filter
Procedure
- Make a 10% detergent solution consisting of 100ml Murphy's Oil Soap and 15 g non-iodized salt. Add distilled water to make a final volume of 1000 ml.
- Coarsely chop onions and then use blender to cut onions into small pieces (about 1cm x 1cm size or less).
- Measure about 50 ml packed onion pieces in a 250 ml beaker or comparable container.
- Add 75ml soap solution to beaker. Mix well by swirling beaker several times.
- Incubate mixture for 15 minutes in hot water bath at 60 to 70 degrees Celsius. A pot of heated water on a hot plate works fine.
- Cool mixture in ice bath for several minutes, occasionally twirling beaker in ice.
- Pour mixture into a blender and fasten the lid. Blend mixture for 30 seconds at low speed.
- Pour mixture into 250ml beaker or comparable container. Allow it to stand in ice until cool. Swirl beaker occasionally.
- Pour mixture through four single layers of cheesecloth (or a coffee filter) in a funnel into a 250ml beaker or comparable container, taking care to leave any foam behind. The filtered liquid is the onion liquid.
- Add an equal volume of ice-cold rubbing alcohol to the onion liquid.
- Gently swirl mixture until a white DNA precipitate appears in the beaker.
- Spool out the DNA by rotating a glass rod or plastic stick (or toothpick) in one direction only in the beaker, allowing the DNA to wrap around the rod or stick.
- Gently ease off the DNA into a 50ml beaker or small container of rubbing alcohol for storage. The DNA can be stored in a covered container indefinitely in the refrigerator.
Questions to think about......
In this lab, you seperated out the DNA from the other cellular components. Many of the materials in this lab were necessary to seperate out various substances like cellulose and lipids from the nucleic acids of DNA.
- Why is a soap solution used?
- Why is rubbing alcohol added to the onion liquid?
- How would you design a procedure to isolate DNA from a blood sample?
Why is this useful?
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