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Q.
Enzyme 'Tag polymerase' used in $PCR$, has been isolated from bacterium
Biotechnology : Principles and Processes
Solution:
The final step of $PCR$ is extension, wherein Taq $DNA$ polymerase (isolated from a thermophilic bacterium Thermus aquaticus) synthesises the $DNA$ region between the primers, using $DNTPs$ (deoxynudeoside triphosphates) and $Mg^{2+}$. The primers are extended towards each other so that the $DNA$ segment lying between the two primers is copied. The optimum temperature for this polymerisation step is $72^°C$. Taq polymerase remains active during high temperature induced denaturation of double stranded $DNA$.