Third step of PCR; Taq polymerase builds copies of DNA at about 72°C. What is this step?

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Multiple Choice

Third step of PCR; Taq polymerase builds copies of DNA at about 72°C. What is this step?

Explanation:
In PCR, the synthesis of new DNA strands happens during the extension step. After heating separates the DNA strands (denaturation) and primers bind to their targets (annealing), the polymerase—Taq—adds nucleotides to the 3′ end of each primer, building a new complementary strand. This activity is optimized around 72°C, which is why the step is performed at that temperature. So the description—Taq polymerase building copies of DNA at about 72°C—refers to extension, the phase where actual copying occurs. The other stages are denaturation (separating strands) and annealing (primers attaching).

In PCR, the synthesis of new DNA strands happens during the extension step. After heating separates the DNA strands (denaturation) and primers bind to their targets (annealing), the polymerase—Taq—adds nucleotides to the 3′ end of each primer, building a new complementary strand. This activity is optimized around 72°C, which is why the step is performed at that temperature. So the description—Taq polymerase building copies of DNA at about 72°C—refers to extension, the phase where actual copying occurs. The other stages are denaturation (separating strands) and annealing (primers attaching).

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