question_answer 27)

  Which of the following steps are catalyzed by Taq polymerase in a PCRreaction? (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:

                    (c) In polymerase chain reaction polymerization or extension step is catalyzed by Taqpolymerase enzyme. PCR is carried out in the following three steps (i) Denaturation The double-stranded DNA is denatured by applying high temperature of 95o for 15 seconds. Each separated single stranded strand now acts as template for DNA synthesis. (ii) Annealing Two sets of primers are added which anneal to the 3 end of each separated strand. Primers act as initiators of replication. (iii) Extension DNA polymerase extends the primers by adding nucleotides complementary to the template provided in the reaction. A thermostable DNA polymerase (Taq DNA polymerase) is used in the reaction which can tolerate the high temperature of the reaction. All these steps are repeated many times to obtain several copies of desired DNA.