DNA Replication - Semi-Conservative Replication

Semi-conservative replication is a mode of DNA replication in which each daughter DNA molecule consists of one parental (old) strand and one newly synthesized strand.

• Semiconservative replication means each new DNA molecule has one old (parental) strand and one newly synthesised strand.
• This was proved by Meselson and Stahl in 1958 using E. coli and density gradient centrifugation.
• E. coli were first grown in ¹⁵N (heavy nitrogen), so the DNA became heavy.
• When transferred to ¹⁴N (light nitrogen), after first generation a hybrid (¹⁴N–¹⁵N) DNA band was formed.
• After the second generation, two bands appeared (hybrid and light DNA), confirming semiconservative replication.