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DNA Extraction From Bacteria

Charles Geach
Irvin High School
El Paso, Texas

Abstract: Teachers like activities that demonstrate and allow their students to see important topics they are covering . This activity extracts and precipitates DNA from E-coli Bacteria . It is a simple procedure and does not require a lot of time or equipment . It has never failed to produce DNA for my students to see.

Type of activity: Hands -on, Inquiry Lab

Target Audience: Biology, AP Biology, Anatomy /Physiology, Genetics , Biotechnology

Acknowledgements:
This activity was adapted and modified from these sources. The basic techniques and ideas were obtained while I was a Research Associate at Lawrence Berkeley Labs, The Cell Biology Laboratory under the Direction of Dr. Mina Bissel. A Laboratory Activity by Dr. Robert Watson, Cetus Corp. and Nancy Stevens, San Rafael High School, "Extracting and Precipitating DNA" was also modified . Carolina Biological Supply Company, North Carolina - has a similar activity you can purchase using freeze dried bacteria.

Notes to the teacher:
The E-coli may be cultured in other suspensions but Luria broth works the best. One swabful of E-coli placed in 250 ml. of Luria broth will produce plenty of bacteria overnight in 37oC. This Broth may be obtained from biological supply companies. The SDS works well for cell lysing and may also be purchased from companies that sell biotechnology supplies. All the other materials are common supplies most schools have.

The lab will only take one class period and still allow time for discussion.

The spooled DNA may be collected and then used for restriction enzyme digest and electrophoresis experiments if desired.

My students are always impressed that they can actually see DNA. I sometimes have a contest to see which student can spool the most DNA onto their stirring rod.

DNA Extraction From Bacteria

Materials:
    E. Coli suspension (Luria Broth, 37oC overnight)
    1% Sodium Dodecyl Sulfate (SDS)
    Test tubes
    Water Bath (60-65oC)
    Stirring rod
    95% Ethanol (chilled)
    Dropper

Safety: Be careful working with Bacterial culture ! Wash hands!

Procedure:
  1. Add 5 ml. E. Coli suspension to a test tube.

  2. Add 1 ml. of SDS to the Tube with E. Coli, gently rotate and swirl to mix in SDS approx. 5 min.

  3. Stand tube in a 60-65o C water bath for 30 min.

  4. Allow to cool to room temp.

  5. Place a stirring rod into the test tube and add 2 ml. of cold 95% ethanol slowly with the dropper down the stirring rod into the tube.

  6. Hold tube at a 45 degree angle and slowly rotate your stirring rod clockwise (avoid touching sides of tube) approx. 5 min.

  7. Remove rod and immerse rod with bacterial DNA in 95% ethanol for approx. 2 min.

Questions:

  1. What do you think the SDS(a detergent) and the heat are for?
  2. Describe what appears between the alcohol and E. Coli suspension layer?
  3. What happens as the spooling rod is rotated in the E. Coli and alcohol layers?
  4. Describe the appearance and characteristics of the extracted DNA?


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