Genetic engineering
Fall 2011
DNA extraction with Chelex resin
Chelating resins organic polymers coated with organic ions that bind metal ions.
Your extraction, performed under in an alkaline aqueous solution, will bind metal
cations such as Ca2+, Mn2+, and Mg2+. By binding these ions the Chelex material
prevents them from damaging DNA (and interfering with other procedures in which
you might use the DNA sample).
The extraction process involves boiling a sample in a 5% suspension of deionized
water and Chelex® 100. The alkalinity of the suspension and the boiling process
disrupts the cell membranes, destroys cell proteins, and denatures the DNA. The
suspension is then centrifuged, separating the resin and cellular debris from the
supernatant containing the denatured DNA.
Extraction protocol
1. Prepare tissue – in this case a small piece of onion – about 50-100 mg
2. Homogenize the sample, in this case by chopping with a knife. Transfer the
chopped bits to a labeled snap-cap tube.
3. Add 200 L 20% chelex. Use a 1,000 L pipet, but first enlarge the opening in
the pipet tip by cutting off a about 5 mm of it with scissors. Prepare negative
control as well.
4. Place tube in boiling water bath for 10 minutes
5. Spin the tube at 13,000 x g for 3 minutes
6. Carefully draw off the supernatant – do not collect any of the Chelex beads.
Place the supernatant, which contains your DNA sample, in a fresh snap-cap
tube. Label the tube and save for next week.
20% Chelex
 0.12 gram TRIS
 20 gram Chelex
 Add water up to 100 mL
 Autoclave