semiconservative

Semiconservative replication is a mode of DNA replication in which each of the two daughter DNA molecules contains one parental (old) strand and one newly synthesized strand. After the double helix is unwound at replication origins, each parental strand serves as a template for the synthesis of a complementary new strand. In both prokaryotes and eukaryotes, replication uses DNA polymerases that add nucleotides to the 3' end of a growing strand, proceeding in the 5' to 3' direction and forming two replication forks that move outward from origins.

The process is semi-discontinuous. The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously as short segments known as Okazaki fragments. These fragments are later joined by DNA ligase. RNA primers laid down by primase initiate synthesis on both strands; the RNA primers on the lagging strand are removed and replaced with DNA. The overall mechanism relies on coordinated activity of helicase, primase, DNA polymerases, ligase, and other factors that ensure accurate and efficient replication.

Historically, the semiconservative model was proposed by Watson and Crick in 1953 and confirmed experimentally by Meselson and Stahl in 1958 using isotopic labeling and density gradient centrifugation in Escherichia coli. The concept remains central to understanding how cells copy their genomes with high fidelity. Semiconservative replication applies to both bacterial chromosomes and eukaryotic chromosomes, with variations in origin usage and replication timing across species.