leadingstrand

Leading strand is the DNA strand synthesized continuously during DNA replication. It is built in the 5' to 3' direction toward the replication fork, using the template strand that runs 3' to 5' in the same direction. As the double helix unwinds, the leading strand can be extended in a single, uninterrupted chain by a high-processivity DNA polymerase (for example, DNA polymerase III in bacteria or DNA polymerase epsilon in eukaryotes). The process typically begins with a short RNA primer laid down by primase; once synthesis starts, the polymerase adds nucleotides matching the template and advances with the advancing fork.

In contrast to the leading strand, the lagging strand is synthesized discontinuously as short Okazaki fragments, each initiated by a primer and later joined by DNA ligase. The coordination of leading- and lagging-strand synthesis occurs within the replisome, a multi-protein complex that includes helicase to unwind DNA, primase to lay primers, DNA polymerases, sliding clamps, and clamp loaders to enhance processivity.

Significance and maturation: the leading strand’s continuous synthesis allows rapid replication of the genetic material in the direction of fork movement. After replication, RNA primers are removed, gaps filled with DNA, and fragments of the lagging strand are joined to form a complete double helix. The distinction between leading and lagging strands reflects the antiparallel nature of DNA and the 5' to 3' directionality of DNA synthesis.