In PCR, DNA is denatured using high temperature. At the start of PCR, the DNA from which a segment is to be amplified, an excess of the two primer molecules, the four deoxyriboside triphosphates and the DNA polymerase are mixed together in the reaction mixture that has appropriate quantities of Mg++. The following operations are now performed sequentially: (1) Denaturation: The double stranded target DNA is heated to a temperature between 90-98 degree Centigrade that ensures denaturation. (2) Annealing: annealing of a primer to the complementary sequences in the DNA. (3) Amplification: the cycle of DNA amplification is repeated again and again.