Why must a cell be made ‘competent’ in biotechnology experiments? How does calcium ion help in doing so?

(a) Why must a cell be made ‘competent’ in biotechnology experiments? How does calcium ion help in doing so?

(b) State the role of ‘biolistic gun’ in biotechnology experiments.

Answer (a) Competent host is essential for transformation with recombinant DNA. Since DNA is a hydrophilic molecule, it cannot pass through membranes, so the bacterial cells must be made capable to take up DNA i.e., made competent. This is done by treating them with a specific concentration of a divalent cations, such as calcium which increases the efficiency with which DNA enters the bacterium through pores in its cell wall. Recombinant DNA (rDNA) can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42°C (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA.

Other methods are:

(i) Microinjection : DNA is inserted through microneedles or micropipettes.

(ii) Electroporation : Electric impulse induce transient pores.

(iii) Gene gun or biolistic : DNA coated with microscopic pellets of gold or tungsten is shot with high velocity into target cells.

(b) Biolistic gun helps in the process of gene transfer into the host cell without using a vector. In biolistic method or gene gun method, tungsten or gold particles, coated with foreign DNA are bombarded into target cells at a very high velocity. This method is suitable for plants, but is also used to insert genes into animal that promote tissue repair into cells (particularly cancer of mouth) near wounds. It has made great impact in the field of vaccine development.