The DNA Polymerase Used in PCR Comes from the Bacterium

question 7

Multiple Choice

The DNA polymerase used in PCR comes from the bacterium thermophile Thermus aquaticus, and is called Taq polymerase. Why is this enzyme used, and not a DNA polymerase from an organism such as E. coli?

• A) The DNA synthesis step of the PCR cycle occurs at 95ᵒC; Taq polymerase is from a bacterium that grows in high temperatures and can function at this temperature, while DNA polymerase from a mesophile such as E. coli would be denatured at this temperature.
• B) The DNA synthesis step of the PCR cycle occurs at 72ᵒC; Taq polymerase can function at this temperature, while DNA polymerase from a mesophile such as E. coli requires significantly higher temperatures in order to function correctly.
• C) E. coli is an RNA organism and therefore depends on RNA polymerase for its replication cycle; it is not possible to obtain DNA polymerase from this bacterium.
• D) The DNA synthesis step of the PCR cycle occurs at 72ᵒC; Taq polymerase is from a bacterium that grows in high temperatures and can function at this temperature, while DNA polymerase from a mesophile such as E. coli would be denatured at this temperature.
• E) DNA polymerase from Thermus aquaticus is a very active enzyme. It is able to synthesize DNA at a faster rate than any other known DNA polymerase which is important because the key to successful PCR is a speedy reaction.

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