What is the advantage of using a thermostable enzyme in PCR?

• A. It would be inhibited by high temperatures
• B. It would require additional cooling after each cycle
• C. It would denature more quickly than non-thermostable enzymes
• D. It would not be denatured at high temperatures and could function during heating

Answer: (D)

PCR relies on repeated heating to separate DNA strands, followed by cooling and extension. A thermostable DNA polymerase stays active at those high denaturation temperatures, so it can synthesize new DNA during the extension step in every cycle. This means the reaction can run automatically through many cycles without needing to add fresh enzyme or pause for cooling. If the enzyme weren’t thermostable, it would denature during heating and lose activity, making amplification inefficient or impossible. The other options describe outcomes that don’t occur with a thermostable enzyme: being inhibited by high temperatures, requiring extra cooling after each cycle, or denaturing more quickly than a non-thermostable enzyme.