Final answer:
During DNA replication, unwinding of DNA exposes template strands in opposite directions. This leads to continuous synthesis of the leading strand in the 5' to 3' direction, while the lagging strand is synthesized in short fragments in the opposite direction.
Step-by-step explanation:
The unwinding of DNA during replication results in two template strands being exposed in opposite directions. One template strand is exposed in the 5' to 3' direction, while the other is exposed in the 3' to 5' direction.
This results in the leading strand being synthesized continuously in the 5' to 3' direction, towards the replication fork. On the other hand, the lagging strand is synthesized in short fragments, called Okazaki fragments, in the direction away from the replication fork.
Only one new DNA strand is synthesized continuously in the leading strand, while the lagging strand is synthesized in fragments. This is due to the antiparallel nature of the DNA double helix and the requirement of DNA polymerase to add nucleotides only in the 5' to 3' direction.