During PCR, which statement describes the step that allows binding of nucleotides and primers to the DNA template?

• A. Adding primers.
• B. Heating to denature DNA.
• C. Cooling to allow binding of nucleotides/primers.
• D. Adding nucleotides.

Answer: (C)

The step being described is the annealing phase. After heating to separate the DNA strands, lowering the temperature allows primers to find and bind to their complementary sequences on the single-stranded templates. This binding creates the starting points for DNA synthesis, which is carried out in the next phase as the polymerase adds nucleotides to extend from the primers. While primers must be added, their binding depends on cooling to an appropriate annealing temperature; nucleotides are incorporated later during extension, not during annealing. The denaturation step is about separating strands, and adding nucleotides happens during extension, not the binding step.