Question

The term “competent” refers to
(a) Increasing the competition between cells
(b) Making cells impermeable for DNA
(c) Increasing the efficiency with which DNA enters the bacterium through pores in its cell wall
(d) Making cells permeable for divalent cations

Answer 1

Hint: DNA is hydrophilic and lipophobic as it is negatively charged and cannot be directly introduced in a host cell. “Competent” term is related to recombinant DNA technology and is essential for transformation.

Complete answer:
“Competent” term is related to increasing the efficiency with which DNA can enter the bacterial cells. After the recombinant DNA is synthesized it has to be taken up by bacterial cells so that the gene product can be obtained. This is done by making the cells competent which means making them actively take up the recombinant

Additional Information:
Several methods are used to make the cell take up the recombinant DNA:
Treatment with divalent cations such as calcium ion, at a specific concentration. The divalent cations increase the uptake of DNA through the cell wall pores. The cells are kept on ice, followed by a heat shock where they are temporarily kept at moderately high temperatures and then again placed on ice.
Microinjection: Foreign DNA is injected directly inside the nucleus of animal or plant cells using needles or micropipettes.
Gene Gun or Biolistic of Particle Gun: Here the recombinant DNA is covered by microscopic pellets of gold or tungsten and fired into the target cells with high velocity. Mostly used for plant cells.
Direct DNA injection: Recombinant DNA is directly injected into the cells.
Electroporation: Electrical impulses are targeted to the cell which generates temporary transient pores in the cell membrane of plant cells and through these pores DNA is readily taken up.

So, the correct answer is,” The term ‘competent’ refers to increasing the efficiency with which DNA enters the bacterium through pores in its cell wall.”

Note: The different techniques used for making the host cell take up recombinant DNA are for different types of cells. Microinjection and direct DNA injection are used in animal cells like oocytes, eggs, and embryos, biolistics and electroporation are used for plant cells. Sometimes the biolistic method is also used in animal cells when the genes promote tissue repair, for reduction of healing time.