Continuous & Discontinuous DNA synthesis
RNA primers are added to both strands of DNA in the 5'3' direction. The Replication Fork (RF) opens unidirectionally: in this diagram, it is shown as opening to the right. The RNA primers are then extended in the 5'3' direction on both strands as DNA synthesis proceeds. On the leading strand, synthesis is continuous because the primer is extended without interruption into the replication fork as it continues to open to the right. On the lagging strand, synthesis is discontinuous, since new RNA primers must be added as the opening of the replication fork continues to expose new template.
All text material © 2004 by Steven M. Carr