competent cell preparation? - (Sep/30/2009 )

what makes a normal cell to become competent in CaCl2 method? i mean the mechanism. what's so special in CaCl2 that we can't use MgCl2 which is more natural for an E.coli cell?

when we make competent cells, what we do is to desestabilize the membrane biochemically so we make it
more liable to penetrance. During transformation of competent cells, the heat shcok literally make pores in pretreated membrane, so the foreign DNA can penetrate in the cell.
and your answer is: The addition of CaCl2 to a cell suspension promotes the binding of plasmid DNA to the cell surface, which can then pass into the cell.