Replication of Protosomes and Chromosomes

• The replication of DNA is semiconservative, involving a single origin of replication in prokaryotes and multiple origins of replication in eukaryotes. • Synthesis of new DNA occurs by copying an existing template through the addition of 5′-nucleoside monophosphate units to the 3′OH moiety of a primer sequence. • Many proteins are involved in the replication process, and the enzymatic activities are the same in prokaryotes and eukaryotes. • The high fidelity of DNA replication is the result of several different postreplicative editing activities that remove errors. • Any single DNA segment is usually replicated only once per cell cycle, and the assembly of chromatin after DNA replication in eukaryotes is a critical period for competition between transcription-control factors and histones. • Developmentally regulated deviations from the “once only per cell cycle” rule for DNA replication can lead to amplification of regions of the genome.