How is a bacterial cell made ‘competent’ to take up DNA?

Since, DNA is a hydrophilic molecule, it cannot pass through all cell membrane.

In order to make bacterial cells capable to take up DNA, they are treated with specific concentration of a divalent cation such as Calcium, which increases the efficiency with which the DNA enters the bacterium through the pores in its cell wall.

rDNA can be sent into such type of cells by following certain steps:

_• incubating the cells with DNA on ice

_• placing them briefly at 42˚C

_• placing them again on ice.