After the primer is in place on a single, unwound polynucleotide strand, DNA polymerase wraps itself around that strand, and it attaches new nucleotides to the exposed nitrogenous bases.

the helix structure is unwound special molecules break the weak hydrogen bonds between bases, which are holding the two strands together this process occurs at several locations on a DNA molecule ...

Areas where DNA is unwound contain active genes coding for proteins that serve important functions within the cell. When gene activity changes, the proteins your cells produce also change.