What does the annealing step in PCR involve?

The annealing step in PCR, or Polymerase Chain Reaction, refers specifically to the phase when primers bind to the complementary sequences on the single-stranded DNA templates. Following the denaturation step, where the double-stranded DNA is separated into two single strands through heating, the temperature is lowered during the annealing step. This decrease in temperature allows the primers, which are short sequences of nucleotides designed to be complementary to the target DNA, to attach firmly to their respective sequences on the single-stranded templates.

This binding is critical as it sets the stage for the next step in the PCR cycle, which is the extension or synthesis of new DNA strands. The efficiency of primer annealing can significantly influence the specificity and yield of the PCR product. It's crucial that the temperature is optimal to ensure that primers bind correctly, maximizing the likelihood of amplification of the desired DNA sequence. Thus, the precise role of the annealing step is truly centered around the binding of primers to DNA.