Step 3.

The temperature is raised to be optimal for the DNA polymerase. The heat-stable polymerases used for PCR typically have an optical temperature in the range of 65-75 degrees C.

Most proteins that we are familiar with would not survive the 90+ degree denaturation step. However, the use of these heat-stable polymerases (obtained from thermophiles, e.g., bacteria living in hot springs) allows several sequential cycles of denaturation/primer extension without the need to add fresh polymerase to the reaction after each cycle.

Go back to Step 2