The DNA-dependent DNA polymerases catalyse polymerisation only in one direction, that is 5′ —> 3′. This creates some additional complications at the replicating fork. Consequently, on leading strand (the template with polarity 3′ —> 5′), the replication is continuous, while on the lagging strain (the template with polarity 5′ —> 3′), it is discontinuous. The discontinuously synthesised fragments are later joined by the enzyme DNA ligase.