Question

Describe the role of Calcium chloride in the preparation of competent cells.

Answer 1

Hint:- Deoxyribose nucleic acid or DNA is a hydrophilic molecule which can not be passed through the cell membrane easily. In order to do this, there are certain treatments made in the host cells so that they become competent to take up that desired DNA.

Complete Answer:- This mainly includes the chemical and physical treatments given in order to facilitate the entry of the desired DNA into the host cell. DNA molecules can be forced to enter into the genome only in those cells that do not have cell walls around them. The naked protoplasts are mixed with the molecules of plasmid DNA containing our desired foreign gene. The two of them are fused in a transformation medium rich in divalent ions like calcium, magnesium followed by the 20 percent ethylene glycol(PEG) solution, in order to promote the frequency of transformation. This chemical method causes increases in calcium ions.
Additional information: There are several other techniques to make the cell competent like electroporation, gun method, and microinjection. In electroporation, the desired DNA is introduced into the cells by making minute pores in the cell membrane of the plant. Gun methods involving gold or tungsten coated with DNA are aimed into the plant cells using particle gun devices at a very high velocity. In microinjection technique, the desired DNA is directly injected inside the nucleus of the cell.

Note:- Gun method is also known as biolistic technique. Several crops like rice, maize etc have now been transformed using this technique. A cell capable of taking up DNA from the medium is known as a competent cell.