Question

Which of the following steps are catalysed by Taq polymerase in a $PCR$ reaction?

• A. Denaturation of template $DNA$
• B. Annealing of primers to template $DNA$
• C. Extension of primer end on the template $DNA$
• D. All of the above

Answer 1

Answer: (C)

The final step of $PCR$ is extension, wherein Tag $DNA$ polymerase (isolated from a thermophilic bacterium Thermus aquaticus) synthesises the $DNA$ region between the primers, using $dNTPs$ (deoxynudeoside triphosphates) and $M{g}^{2+}$. 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 $DNA$.