Stage Three - Transformation of DNA into host cells

• Once the DNA has been incorporated into some of the plasmids, the plasmids must be mixed with bacterial cells and calcium ions in a medium, during process known as transformation.
• By mixing the plasmids with the calcium ions and providing a change in temperature, the bacterial cells membranes in the medium become more permeable, allowing plasmids to pass through the cell surface membrane and into the cytoplasm.
• Not all bacterial cells in the medium will possess the DNA fragments with the desired gene for the desired protein. This is because : only a few bacterial cells will take up the plasmids when mixed, some plasmids will close without taking up any DNA fragments, sometimes the DNA fragment ends join together to form its own plasmid.