Competent Host (For Transformation with Recombinant DNA)
(i) DNA being a hydrophilic molecule, cannot pass through cell membranes.
(ii) The bacteria should be made competent first, to accept the DNA molecules by treating them with a specific concentration of a divalent cation like calcium which increases the efficiency with which DNA enters the cell through the pores in its cell wall.
(iii) Recombinant DNA can be forced into such cells by incubating the cells on ice, followed by placing them briefly at 42°C (heat shock) and then putting them back on ice. This facilitates the entry of recombinant DNA in the bacterial cell.
