In the annealing (second) step of polymerase chain reactions (PCR), temperature is lowered to 55-65°C. The reason for lowering the temperature is to:
Correct answer: D. Allow the binding of primers to their complementary sequences
- A. Activate the Taq polymerase enzyme
- B. Extend the primers to synthesise new strands of DNA
- C. Make single-stranded DNA template for the next step
- D. Allow the binding of primers to their complementary sequences
Explanation
During the annealing step of PCR, the temperature is lowered to approximately 55-65°C to allow primers to bind or anneal to their complementary sequences on the single-stranded DNA. This is crucial for the next step where Taq polymerase extends the primers and synthesizes new DNA strands. Option D is correct as it describes this process. Option A is incorrect because Taq polymerase activation primarily occurs during the extension phase at around 72°C. Option B is incorrect because primer extension is not the purpose of the annealing step. Option C is incorrect as the formation of single-stranded templates occurs during the denaturation step, not annealing.
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