Describe the steps that constitute one cycle of reactions in PCR.

Step 1: Denaturation

In this process, the two strands in the DNA double helix needs to be separated like in DNA replication. This separation takes place by increasing the temperature of the mixture. As a result,  the hydeogen bonds between the complementary DNA strands break. This step is called denaturation.

Step 2: Annealing

In this process, primers bind to the target DNA sequences and it initiates polymerisation. This can occur only when the temperature of the solution is low. One primer binds to each strand.

Step 3: Extension

New strands of DNA are synthesized using the original strands as templates. The enzyme DNA polymerase joins thee free DNA nucleotides together. This enzyme is also called Taq polymerase and it is isolated from a thermophilic bacteria called Thermus aquaticus. The sequence of nucleotides in the original (template) DNA strand determines the order in which the free nucleotides are added.

One cycle of PCR results in the formation of two double-stranded sequences of target DNA, in which each contains one newly made strand and one original strand.