DNA-dependent DNA polymerases catalyse polymerisation only in one direction, that is 5'->3'. This creates a problem at the replication fork. On one strand (the template with polarity 3'->5'), replication is continuous (leading strand). On the other strand (template with polarity 5'->3'), replication is discontinuous. These discontinuously synthesised fragments (Okazaki fragments) are formed on the lagging strand and are synthesized in the 5'->3' direction, which is away from the opening replication fork .