Final answer:
DNA is replicated by a suite of enzymes, key among them being DNA polymerase, which adds nucleotides to the growing DNA strand. DNA polymerase I substitutes RNA nucleotides with DNA nucleotides. For RNA genomes, RNA replicase is used.
Step-by-step explanation:
DNA is replicated in cells by a host of enzymes, each with a specialized role in the replication process. The enzyme responsible for synthesizing new DNA strands by adding nucleotides complementary to the DNA template strand is known as DNA polymerase. In prokaryotes such as E. coli, this role is chiefly fulfilled by DNA polymerase III. The process begins with the short RNA primers, synthesized by primase, after which DNA polymerase III adds nucleotides in a 5′9' direction to synthesize the new DNA strand.
DNA helicase unwinds the DNA double helix, and DNA ligase has the task of joining the discontinuous fragments of the lagging strand, also known as Okazaki fragments.
It is important to note that the enzyme that substitutes RNA nucleotides in a primer with DNA nucleotides and also completes the replication process of DNA strands is DNA polymerase I in prokaryotes. For viral genomes made of RNA, an enzyme called RNA replicase is used for replication.