The protein helicase attaches to and breaks apart the hydrogen bonds between the bases on the DNA strands, thereby pulling apart the two strands. As it moves along, it continues breaking these hydrogen bonds and separating the two polynucleotide chains. Another enzyme called primase briefly attaches to each strand and assembles a foundation at which replication work can begin. DNA polymerase wraps itself around that strand, and it attaches new nucleotides. In this way, the polymerase assembles a new DNA strand on top of the existing one. As polymerase makes its way, it relies on the nucleotides surrounding to make a new strand. They are paired with partner nucleotides , usually A & T, C & G. This is called a complementary base pairing.
