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'? @Biology

Answer 1

DNA is a negatively-charged molecule. Also cell membranes are negatively charged. So... if you get to pierce the membrane you will still have a problem. How can you push the negatively-charged DNA through a negatively-charged pore??? Of course two negatively charged molecules will tend to push themselves away so the DNA and the membrane will never be close enough to allow the entrance of the genetic material. BUT if you put some CaCl2 into the reaction mixture, which is an acquous solution, the CaCl2 will "split" giving 2Cl- (which will not disturb, since they'll stay well away from the pore because of its own charge) and Ca2+. This last ion will be attracted by the negatively charged DNA and will "cover" it, hiding its negative charge. So now DNA is a neutral molecule (although a fake one) and can enter the pore. and so you have transformation!