- Since DNA is a hydrophilic molecule, it cannot pass through cell membranes so the bacterial cells must first be made ‘competent’ to take up DNA.
- Several methods are followed to make the bacterial cells competent-
- Treating them with a specific concentration of a divalent cation, such as calcium, which increases the efficiency with which DNA enters the bacterium through pores in its cell wall.
- Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42oC (heat shock), and then putting them back on ice which enables the bacteria to take up the recombinant DNA.
- Recombinant DNA can be directly injected into the nucleus of an animal cell by a method called micro-injection.
- In biolistics or gene gun method, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA
- Disarmed pathogen vectors can be allowed to infect the cell to transfer the recombinant DNA into the host.
Fig. DNA is injected into the nucleus of the host cell by the process of micro-injection.