Final answer:
In DNA replication, the leading strand requires a primer only at the 5'-end for continuous synthesis, while on the lagging strand, each Okazaki fragment needs a new primer for its discontinuous synthesis.
Step-by-step explanation:
On the leading strand, where DNA synthesis is continuous, a primer is required only at the 5'-end of the newly synthesized strand. On the lagging strand, where replication is discontinuous, a new primer must be generated at the beginning of each Okazaki fragment. The leading strand can be synthesized continuously because the DNA polymerase enzyme works in the 5' → 3' direction, which is the same direction as the replication fork is moving. In contrast, the DNA polymerase on the lagging strand has to work in the direction opposite to the replication fork, requiring multiple primers to initiate the synthesis of short Okazaki fragments.
After the RNA primers are laid down, DNA polymerase extends the DNA strands by adding nucleotides. On the lagging strand, each primer starts the creation of a new Okazaki fragment. Once the fragments are synthesized, the RNA primers are removed, and the gaps are filled with DNA nucleotides, and finally, an enzyme called DNA ligase seals the sugar-phosphate backbone, finalizing the DNA replication.