Transformation is the process by which the genetic material of a cell is changed by the introduction of DNA from outside. There are several ways to prepare competent cells for transformation follows as calcium chloride, ice, and heat treatment.

Calcium chloride:

When bacterial cells are placed in the salt solution containing calcium chloride, the positively calcium ions are attracted to both the negatively charged cell membrane and DNA molecules in the solution and become neutralise charge on the membrane. As a result the DNA plasmid to enter through the cell membrane

Heat shock

The plasmid DNA can be removed from celld by heat shock method. In this method, the cells and DNA are incubated with the calcium chloride solution on ice. Then, the cell or DNA solution is removed from the ice bath and briefly heated to 42 °c.