Question

DNA being hydrophilic cannot pass through the cell membrane of a host cell. Explain how does recombinant DNA get introduced into the host cell to transform the latter.

Answer 1

The cell is made competent by the following methods:

a. Chemical method

• The cell is treated with specific concentration of a divalent cation such as calcium to increase pore size in cell wall.

• The cells are incubated with recombinant DNA on ice, followed by placing them briefly at 42°C and then putting it back on ice. This is called heat shock treatment.

• The bacteria now take up the recombinant DNA.

b. Physical methods

The physical methods include

• Micro-injection method: Recombinant DNA is directly injected into the nucleus of an animal cell.

• Biolistics or gene gun method: Cells are bombarded with high velocity microparticles of gold or tungsten coated with DNA in plants.