Question
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The source of a Taq polymerase used in PCR is a
A. Thermophilic fungus
B. Mesophilic fungi
C. Thermophilic bacterium
D. Halophilic bacterium

Answer
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Hint: Taq polymerase was the first heat-stable DNA polymerase discovered by D. Brock and H. Freeze, in 1969. Taq polymerase is used for amplification of DNA during polymerase chain reaction. This enzyme is thermostable and remains active at high temperatures.

Complete Answer: Taq polymerase is a thermostable DNA polymerase obtained from the thermophilic bacterium, which normally lives in hot springs. The function of Taq DNA polymerase in PCR is to amplify or synthesize DNA or gene of interest for various down-stream applications.
During the DNA replication, new strands of DNA are synthesized, using the existing strands as templates by using the DNA polymerase enzyme which is also known as ‘Taq polymerase’. There are generally the following steps involved in a polymerase chain reaction:
Denaturation: it involves strand separation
Annealing: in this step primer binding takes place
Extension: synthesis of new DNA strands
Exponential Amplification: Taq polymerase is involved in this step which leads to the production of multiple copies
During the first cycle, two copies are produced which further goes on multiplying exponentially.

So, the correct answer is option ‘C’.

Additional information:
The end products of PCR amplification are unreliable because of “plateau effect”. It occurs when the PCR reaction fails to amplify DNA segments further due to certain reasons.

Note: Taq polymerase is the most common enzyme used for PCR amplification because of a specific reason. This enzyme is extremely heat resistant. This heat stability makes Taq polymerase ideal for PCR and hence for the production of copies from even the smallest of DNA segments.