PathwayStep472 PathwayStep484 PathwayStep507 DNA replication initiation Switching of origins to a post-replicative state Synthesis of DNA Reactome Database ID Release 4369239 Reactome, http://www.reactome.org ReactomeREACT_2014 The actual synthesis of DNA occurs in the S phase of the cell cycle. This includes the initiation of DNA replication, when the first nucleotide of the new strand is laid down during the synthesis of the primer. The DNA replication preinitiation events begin in late M or early G1 phase. DNA strand elongation