Which enzyme builds new DNA strands during DNA replication?

DNA polymerase builds new DNA strands during DNA replication.

The enzyme adds complementary nucleotides to a growing strand, using an existing DNA strand as a template. It can add nucleotides only to the free 3′ end, so new DNA is synthesized in the 5′-to-3′ direction. This directional rule contributes to the leading- and lagging-strand arrangement at a replication fork.

Many DNA polymerases also proofread newly added bases. Their error-checking activity helps keep mutation rates low, although replication is not completely error-free. In cells, several specialized polymerases divide tasks such as genome copying, repair, and damage bypass.

DNA polymerase is often confused with other replication enzymes. Helicase separates the two DNA strands, primase makes short RNA primers, and DNA ligase joins certain DNA fragments. RNA polymerase, meanwhile, makes RNA from a DNA template during transcription.