Leading & lagging strand synthesis, Okazaki fragments, helicase unwinding
Helicase unwinds the double helix at ~1000 bp/s. Leading strand synthesis proceeds continuously 5'→3'. Lagging strand is synthesized in ~1–2 kb Okazaki fragments, each initiated by an RNA primer (primase). Polymerase δ replaces primers with DNA; ligase seals nicks.