Final answer:
The most commonly used thermostable DNA polymerase in PCR is Taq polymerase, which is derived from the thermophilic bacterium Thermus aquaticus and can withstand high temperatures required for PCR.
Step-by-step explanation:
The most commonly used thermostable DNA polymerase in PCR (Polymerase Chain Reaction) is Taq polymerase. Taq polymerase is an enzyme that exhibits high stability at the high temperatures typically employed during the PCR process. Isolated from the thermophilic bacterium Thermus aquaticus, which thrives in the hot springs of Yellowstone National Park, Taq polymerase has become the standard polymerase for PCR because it does not denature even at temperatures as high as 98 °C. It is functionally active in a wide temperature range from 22°C to 89°C, with an optimum activity temperature of 72°C. Due to these properties and the enzyme being able to withstand the multiple cycles of heating and cooling that characterize the PCR process, Taq polymerase doesn't need to be added after each replication cycle, making the PCR technique much more efficient and practical.