The correct answer to this question is option A – Extension or elongation The extension/elongation phase is where nucleotide triphosphates 9dNTPs) are added to the growing DNA strand. This is the final phase of PCR. The temperature is increased to about 72 degrees Celsius. This is the optimal temperature required for the activity of Taq DNA polymerase.
Taq DNA pol is the enzyme that added new DNA. A buffer is also required to create the right chemical environment for the function of Taq DNA polymerase. The annealing phase is the second phase in PCR. It is the phase before the extension phase. Temperature is lowered as this phase and primers attach to a specific segment of the DNA. The first phase of PCR is the Denaturation/ Separation phase. Temperature is increased to the hydrogen bonds between DNA strands.
Extension/elongation step: The temperature at this step depends on the DNA polymerase used; Taq polymerase has its optimum activity temperature at 7580 °C, and commonly a temperature of 72 °C is used with this enzyme. At this step the DNA polymerase synthesizes a new DNA strand complementary to the DNA template strand by adding dNTPs that are complementary to the template in 5 to 3 direction.