STEP 3 Enzymes known as DNA polymerases are responsible for creating the new strands by a process called elongation . After the primer is in place on a single , unwound polynucleotide strand , DNA polymerase wraps itself around that strand , and attaches new nucleotides to the exposed nitrogenous bases . As DNA polymerase makes its way down the unwound DNA strand , it relies upon free-floating nucleotides surrounding the existing strand to build the new strand . The nucleotides that make up the new strand are paired with the nucleotides of the existing strand in a complementary fashion ( A with T and G with C ). This phenomenon is known as complementary base pairing and it results in the production of two complementary strands of DNA - a new complementary DNA strand built atop an existing one .
STEP 4 Once both the continuous and discontinuous strands are formed , an enzyme called exonuclease removes all the RNA primers from the original strands , replacing them with the appropriate bases . Another enzyme called DNA ligase joins the Okazaki fragments together forming a single unified strand . Then , a different exonuclease “ proofreads ” the newly formed DNA to check , remove and replace any errors . Finally , a specialized enzyme called telomerase catalyzes the synthesis of telomere sequences to cap the ends of the DNA strands .
For the leading strand ( running 3 ’ to 5 ’), formation of the new complementary strand is continuous as replication occurs in the 5 ’ to 3 ’ direction .
For the lagging strand ( running 5 ’ to 3 ’), formation of the new strand is discontinuous . In this case , multiple primers attach to the lagging strand and polymerases then add pieces of DNA , called Okazaki fragments , to the strand in between the primers . In this way , the new complementary strand is created with numerous disjointed pieces .
Once completed , the parent strands and their complementary DNA strands coil into the familiar double helix shape . In the end , replication produces two daughter DNA molecules , each composed of one strand from the parent molecule and one newly synthesized strand .