DNA replication is slightly slower in the lagging strand because the DNA polymerase enzyme can only add new nucleotides in one direction. On the leading strand, the enzyme can continuously add nucleotides as the replication fork opens up. However, on the lagging strand, new Okazaki fragments are continuously being synthesized in the opposite direction of the replication fork, causing a slower overall rate of replication. This process of adding new fragments and connecting them together ultimately slows down the overall replication of the lagging strand compared to the leading strand.
