Which enzyme is primarily involved in the synthesis of new DNA strands during replication?

The enzyme primarily responsible for synthesizing new DNA strands during replication is DNA polymerase III. This enzyme plays a crucial role in the DNA replication process, where it adds nucleotides to the growing DNA strand by complementary base pairing with the template strand. DNA polymerase III has a high processivity, allowing it to synthesize long stretches of DNA quickly and efficiently.

During replication, DNA is unwound to create a replication fork, and it is at this site that DNA polymerase III synthesizes new strands in a 5' to 3' direction. It is also equipped with proofreading abilities, which help to ensure the accuracy of DNA replication by correcting errors as they occur.

In contrast, DNA ligase functions to join Okazaki fragments on the lagging strand after they have been synthesized by other polymerases. DNA polymerase I has a role in replacing RNA primers with DNA but is not the main enzyme for bulk DNA synthesis during replication. RNA polymerase, meanwhile, is involved in the transcription process, synthesizing RNA from a DNA template, not in DNA replication.