Question

Why does CaCl2 need to be added to cells to make them 'competent'? Why does CaCl2 need to be added to cells to make them 'competent'?

Answer 1

DNA is a negatively-charged molecule. Also cell membranes are negatively charged. The problem would be how to push this charges together? If you put some CaCl2 into the mixture, the CaCl2 will "split" giving 2Cl- and Ca2+. This last ion will be attracted by the negatively charged DNA and will "cover" it, hiding its negative charge. Hope this answers the question.