Here's why:
* PCR requires high temperatures. The PCR process involves cycles of heating and cooling to denature DNA, anneal primers, and extend the new DNA strand. This process requires an enzyme that can withstand these high temperatures without denaturing itself.
* Cellular DNA polymerases are not thermostable. The DNA polymerases found in our cells and most bacteria are optimized for the normal cellular temperature. They would quickly degrade at the high temperatures used in PCR.
Therefore, PCR utilizes a thermostable DNA polymerase, most commonly Taq polymerase, isolated from the thermophilic bacterium *Thermus aquaticus*. This enzyme can withstand the high temperatures needed to denature the DNA template without losing its activity.
Here's a table summarizing the key differences:
| Feature | PCR DNA Polymerase (e.g., Taq) | Cellular DNA Polymerase |
|---------------------|--------------------------------|-------------------------|
| Thermostability | High, can withstand 95°C | Low, denatures at high temperatures |
| Source | Thermophilic bacteria | Eukaryotes/Prokaryotes |
| Used in PCR | Yes | No |
In summary, the thermostability of Taq polymerase is the crucial feature that allows it to function in the harsh conditions of PCR, distinguishing it from cellular DNA polymerases.
