Here's why:
* DNA replication is semi-conservative: This means each new DNA molecule consists of one original strand and one newly synthesized strand.
* Leading strand synthesis: DNA polymerase can only add nucleotides to the 3' end of a growing strand. Since DNA is antiparallel, one strand (the leading strand) can be synthesized continuously in the 5' to 3' direction, following the movement of the replication fork.
* Lagging strand synthesis: The other strand (the lagging strand) is synthesized discontinuously in short fragments called Okazaki fragments, which are later joined together.
So, while both strands are newly synthesized, only the leading strand is synthesized in a continuous manner, hence its name.
