Final answer:
The leading strand in DNA replication extends continuously from a single primer, while the lagging strand requires multiple primers to produce Okazaki fragments. RNA primers are eventually replaced with DNA, and DNA ligase seals the nicks to complete DNA synthesis.
Step-by-step explanation:
In the process of DNA replication, primers are necessary to start the synthesis of a new DNA strand. The leading strand can be synthesized continuously from a single primer, thanks to the directional nature of DNA polymerases, which add nucleotides in a 5' to 3' manner. This means that the leading strand is extended continuously towards the replication fork.
The lagging strand, however, is synthesized discontinuously, due to the antiparallel structure of DNA. To replicate this strand, multiple primers are needed to produce short DNA segments called Okazaki fragments, and each fragment requires a primer. This lagging strand synthesis occurs in a 5' to 3' direction, but effectively moves away from the replication fork as the fork progresses.
The RNA primers used for initiating synthesis, both on the leading and the lagging strands, are later replaced by DNA nucleotides. This task is performed by the exonuclease activity of DNA polymerase I, which also fills in the resulting gaps with DNA nucleotides. Finally, the enzyme DNA ligase seals the nicks, forming stable phosphodiester linkages and thus completing the replication process.