Taq polymerase is a thermostable DNA polymerase that is commonly used in polymerase chain reaction (PCR) due to its high processivity and resistance to high temperatures. Taq polymerase was first isolated from the bacterium Thermus aquaticus, which is found in hot springs, and it has since become an essential tool in molecular biology research.

One of the main reasons why Taq polymerase is used in PCR is because it can withstand the high temperatures required for denaturation and extension of DNA. During the denaturation step of PCR, the double-stranded DNA template is heated to around 95°C to denature the DNA into two single strands. The high temperature would normally denature most DNA polymerases, but Taq polymerase is stable at these temperatures, making it an ideal choice for PCR.

Another reason why Taq polymerase is commonly used in PCR is because it has a high processivity, meaning it can add many nucleotides to the growing DNA strand without dissociating from the template. This makes Taq polymerase an efficient enzyme for DNA synthesis during the extension step of PCR, leading to high yields of the target DNA sequence.

In addition, Taq polymerase has a relatively low error rate, which is important for PCR amplification of a specific target sequence. The error rate of Taq polymerase is estimated to be around 1 in 10,000 nucleotides, which is relatively low compared to other DNA polymerases.

Taq polymerase is also widely available and relatively inexpensive, making it accessible to researchers in various fields of molecular biology. There are also modified versions of Taq polymerase, such as high-fidelity Taq polymerases, which have lower error rates and increased processivity.

However, there are some limitations to the use of Taq polymerase in PCR. One major limitation is its lack of proofreading activity, which means that it cannot correct errors that occur during DNA synthesis. This can result in the introduction of errors, such as nucleotide misincorporations, during the amplification of DNA. In addition, Taq polymerase may not be suitable for amplifying longer DNA sequences or for PCR applications that require higher fidelity.

In conclusion, Taq polymerase is used in PCR due to its high processivity, resistance to high temperatures, and relatively low error rate. Its accessibility and affordability make it a popular choice for PCR applications in molecular biology. However, its lack of proofreading activity may limit its use in certain PCR applications.