DNA Extraction from Onion (the Kitchen Version)

What does DNA look like? You can isolate large amounts of DNA from yellow onions. This is an easy procedure that you can do even at home.

Materials and Equipment

This procedure uses Murphy's Vegetable Oil Soap.

Per class Blender Murphy's Vegetable Oil Soap Hot water bath (60 to 70°C) Rubbing alcohol Salt (non-iodized) Chopped yellow onions Per group Large container of ice Funnel Two 250 ml beakers or comparable containers 50 ml beaker or comparable container Glass stirring rod or plastic stick Cheesecloth

Procedure

1. Make a 10% detergent solution consisting of 100 ml Murphy's Oil Soap and 15 g non-iodized salt. Add distilled water to make a final volume of 1000 ml.

2. Coarsely chop onions and then use blender to cut onions into small pieces (about 1 cm x 1 cm size or less).

3. Measure about 50 ml packed onion pieces in a 250 ml beaker or comparable container.

4. Add 75 ml soap solution to beaker. Mix well by swirling beaker several times.

5. Incubate mixture for 15 minutes in hot water bath at 60 to 70 °C. A pot of heated water on a hot plate works fine.

6. Cool mixture in ice bath for several minutes, occasionally twirling beaker in ice.

7. Pour mixture into a blender and fasten the lid. Blend mixture for 30 seconds at low speed.

8. Pour mixture into 250 ml beaker or comparable container . Allow it to stand in ice until cool. Swirl beaker occasionally.

9. Pour mixture through four single layers of cheesecloth in a funnel into a 250 ml beaker or comparable container, taking care to leave any foam behind. The filtered liquid is the onion liquid.

10. Add an equal volume of ice-cold rubbing alcohol to the onion liquid.

11. Gently swirl mixture until a white DNA precipitate appears in the beaker

12. Spool out the DNA by rotating a glass rod or plastic stick in one direction only in the beaker, allowing the DNA to wrap around the rod or stick.

13. Gently ease off the DNA into a 50 ml 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 ...

1. Why is a soap solution used?

2. Why is rubbing alcohol added to the onion liquid?

3. How would you design a procedure to isolate DNA from a blood sample? Why is this useful?

BIOTECH Project Department of Molecular and Cellular Biology The University of Arizona August 3, 1998 Nadja Anderson, Ph.D. http://biotech.biology.arizona.edu