File:Asymmetry in the synthesis of leading and lagging strands.svg

English: Duplication of the DNA begins with origin unwinding, followed by the synthesis of RNA primers (jagged lines) on both DNA strands. DNA polymerase delta or epsilon extends these primers by adding new DNA (green lines) only in a 5' to 3' direction. On the leading strands, this results in the continuous synthesis of long DNA molecules. Lagging strands, in contrast, are synthesized discontinuously: primers are placed on the template every ~200 nucleotides and extended to form short Okazaki fragments. For simplicity, this diagram does not show the replacement of primers with DNA or the synthesis of telomeres at the chromosome ends.^[1]