The lagging strand of DNA is synthesized in short bursts, producing segments called Okazaki fragments. This discontinuous synthesis occurs due to the antiparallel nature of the DNA strands and the direction in which DNA polymerase can add nucleotides.
DNA polymerase can only add nucleotides to the free 3′ end of a growing DNA strand, synthesizing new DNA in a 5′ to 3′ direction. During DNA replication, the leading strand is synthesized continuously as the DNA unwinds. However, the lagging strand, which runs in the opposite direction, cannot be synthesized continuously. As the replication fork opens up, DNA polymerase must work backward in short segments as more DNA unwinds.
In summary, the lagging strand must be synthesized discontinuously to accommodate the directional limitations of DNA polymerase and the overall antiparallel structure of the DNA double helix.