i. Since, DNA molecules are hydrophilic, they cannot pass through cell membranes. For recombinant DNA to be integrated into the vector or host genome, it is necessary for the DNA to be inserted in the cell. Therefore, making the host cells competent is necessary for biotechnology experiments.
The two ways by which cells can be made competent to take up DNA are:
a. Chemical action -The host cell is treated with a specific concentration of divalent cation, i.e. calcium which increases the pore size in the cell membrane. DNA is then incubated with the treated bacterial cell at 42°C, thereby increasing the efficiency of DNA entering through pores in the cell wall.
b. Heat shock treatment- Incubating the cells with recombinant DNA on ice, followed by a brief treatment of heat at 42°C
and again putting them back on ice. ii. Biolistic guns or gene guns are used to bombarded rDNA loaded on gold or tungsten particles with high velocity. In this way,
the rDNA is delivered to the desired host cells.