CBSE Class 12-science Answered

(i) Each cycle of PCR requires two sets of primers.

Role of primers: Primers are complementary to the regions of DNA. They anneal to both the strands of DNA which are then extended using nucleotides.

Role of DNA polymerase: The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template.

(ii) DNA polymerase used in PCR is thermostable and active even at a temperature of 72C and is called Taq polymerase. It is obtained from the bacterium Thermus aquaticus.