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Chemi-Competent Cells

Competent cells are those that naturally and easily uptake foreign DNA into themselves; an example of a naturally competent cell is E. coli. For all other cells, however, a shock of some sort must be applied. The easiest method is usually the creation of chemi-competent cells, or cells that are made competent through chemical means.

To make cells chemi-competent, a chemical solution that makes them artificially porous must be introduced. A typical method is to place them in a calcium chloride solution at 0 degrees centigrade, which creates ions. At this point, the cells can be stored at -80 degrees centigrade or used immediately.

When they're ready for use, the scientist introduces extracellular DNA to the chemi-competent cell solution. After about a half hour, the entire mixture is exposed to a warmer temperature – depending on the cells, between about five and fifteen degrees centigrade. The shock of sudden heat opens the prepared pores on the cells, allowing the extracellular DNA to enter.

Not all cells can be made chemi-competent; for some, electroshock or even mechanical insertion of foreign DNA is necessary.

Web Resources On Chemi-Competent Cells

Competent Cell Protocol
Preparation of Electrocompetent Cells and Electroporation of Plasmid DNA

Book Resources On Chemi-Competent Cells

Culture of Animal Cells: A Manual of Basic Technique by R. Ian Freshney
Essential Cell Biology: An introducton to the Molecular Biology of the Cell by Alberts & Raff

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