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DNA replication is a semi-conservative process: each daughter molecule consists of one original (template) strand and one newly synthesised strand. The process begins at specific sequences called origins of replication. Helicase unwinds the double helix by breaking the hydrogen bonds between complementary base pairs, creating a replication fork that moves in both directions. Single-strand binding proteins stabilise the separated strands to prevent them from re-annealing. Topoisomerase relieves the torsional stress ahead of the fork. Because DNA polymerase can only add nucleotides to an existing 3' hydroxyl group, primase first synthesises short RNA primers to provide a starting point. DNA polymerase III then reads each template strand in the 3' to 5' direction and synthesises the complementary new strand in the 5' to 3' direction. On the leading strand, synthesis is continuous. On the lagging strand, synthesis occurs in short discontinuous segments called Okazaki fragments (each preceded by its own primer). DNA polymerase I replaces the RNA primers with DNA nucleotides, and DNA ligase seals the nicks between Okazaki fragments. Finally, the two daughter helices wind back up.
answered by Omniscientia Team · 176 words · 18 Mar 2026