DNA replication requires enzymes like DNA helicase, DNA polymerase III, DNA primase, DNA polymerase I, and DNA ligase. DNA helicase splits the DNA double helix at the origin of replication. DNA polymerase III synthesizes new DNA strands using the old strands as templates from 5' to 3' but reads the templates from 3' to 5'. On the lagging strand, DNA primase adds RNA primers that DNA polymerase I then extends into DNA. Finally, DNA ligase forms phosphodiester bonds between Okazaki fragments.