The leading strand is oriented in a way for nucleotides to be added in the 5' to 3' direction. The lagging strands add nucleotides in the opposite direction of 3' to 5' away from the replication fork. Because the lagging strand is being formed backwards, it is made in fragments called okazaki fragments and not a continuous piece like the leading strand. DNA ligase is needed to connect the fragments together and it is not needed in the leading strand. Another difference is the leading strand only needs an RNA primer at the beginning of the strand , but the lagging strand uses RNA primers for each separate fragment.