Question

Define recombinant DNA. Explain any two methods of introducing alien DNA into host cell.

Answer 1

Recomninant DNA is a molecule of DNA that has been modified, either through genetic recombination laboratory techniques.
Methods of introducing alien DNA into host cell:
Electroporation:-
Since DNA is a hydrophilic molecule, it cannot pass through cell membranes. In order to force bacteria to take up the plasmid, the bacterial cells must first be made 'competent' to take up DNA. This is done by 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 $420C$ (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA.
Microinjection:-
Recombinant DNA is directly injected into the nucleus of an animal cell.
Biolistics or gene gun:-
In another method, suitable for plants, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA in a method known as biolistics or gene gun. And the last method uses 'disarmed pathogen' vectors, which when allowed infecting the cell, transferring the recombinant DNA into the host.