DNA Replication (Detailed)

Helicase, primase, DNA polymerase, and leading/lagging strand synthesis

DNA replication is semi-conservative — each new DNA molecule contains one original and one new strand. Helicase unwinds the double helix at the replication fork. Single-strand binding proteins stabilize the separated strands. Primase synthesizes short RNA primers. DNA polymerase III extends primers in the 5'→3' direction. On the leading strand, synthesis is continuous. On the lagging strand, synthesis is discontinuous, producing Okazaki fragments (~1000-2000 bp in prokaryotes). DNA polymerase I replaces RNA primers with DNA. DNA ligase seals nicks between fragments. The result: two identical DNA molecules.