Final answer:
DNA polymerases are responsible for elongating the new DNA strands during replication after the DNA has unwound and a primer has been added. They add nucleotides to the 3'-OH end of the RNA primer and facilitate the formation of both the leading and lagging DNA strands.
Step-by-step explanation:
After DNA has unwound and a primer has been added, DNA polymerases elongate the polynucleotide strand by catalyzing DNA polymerization. DNA polymerase III starts adding nucleotides to the 3'-OH end of the primer. The elongation of both the lagging and the leading strand continues thanks to the action of DNA polymerases.
The primer, synthesized by the enzyme RNA primase, is a short RNA segment complementary to the template DNA. DNA polymerase can then extend this RNA primer, adding nucleotides one-by-one that are complementary to the template strand. On the leading strand, synthesis is continuous, whereas on the lagging strand, synthesis is discontinuous, forming Okazaki fragments. Each fragment begins with a separate primer, and DNA polymerase δ (delta) synthesizes the lagging strand. The RNA primers are eventually removed, the gaps are filled with DNA, and DNA ligase seals these fragments to complete the replication process.