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How bacterial cells are made competent t...

How bacterial cells are made competent to take up DNA?

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Since DNA molecules are hydrophillic they cannot pass through cell membranes. For recombinant DNA to be integrated into vector or host genome it is necessary for the DNA to be inserted in the cell. Therefore, making the host cells competent is necessary in biotechnology experiments.
The two ways by which bacterial cells can be made competent to take up DNA are :
(i) Chemical action By increasing concentration of divalent cation, i.e. calcium which makes pores in the cell membrane. DNA is them incubated with treated bacterial cell at `42^(@)C` thereby increasing the efficiency of DNA entering through pores in cell wall .
Heat shock treatment Incubating the cells with recombinant DNA on ice followed by brief treatment of heat at `42^(@)` C and again putting them back on ice .
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