Which enzyme is heat-stable and used in PCR, extracted from Thermus aquaticus?

The correct answer is Taq polymerase, which is a specific type of DNA polymerase. This enzyme is of significant importance in the process of polymerase chain reaction (PCR) because it is heat-stable and can withstand the high temperatures used during the denaturation step of PCR.

During PCR, the double-stranded DNA is heated to separate the strands, and Taq polymerase, originally obtained from the thermophilic bacterium Thermus aquaticus, remains active even at these elevated temperatures. This stability allows the enzyme to synthesize new DNA strands during the annealing and extension phases of the PCR process without being denatured, which is vital for the amplification of specific DNA sequences.

In contrast, other enzymes like RNA polymerase and ligase have different functions and stability characteristics that do not align with the needs of PCR. RNA polymerase is involved in transcription, while ligase joins DNA fragments together but is not required for the replication of DNA and is generally less heat-stable. Therefore, Taq polymerase is uniquely suited for PCR applications, making it the correct choice.