Final answer:
Primers required for DNA synthesis are short RNA sequences made by primase. On the leading strand, one primer suffices, while on the lagging strand, each Okazaki fragment requires its own primer. These primers are later removed and replaced with DNA, and gaps are sealed by DNA ligase.
Step-by-step explanation:
Primers for partial synthesis of the plus strand DNA during replication are created through the action of an enzyme called primase, which synthesizes short RNA sequences that are complementary to the DNA template. These RNA primers provide a 3'-OH group that DNA polymerases require to initiate the synthesis of DNA nucleotides.
On the leading strand, DNA synthesis can be extended from a single primer. In contrast, on the lagging strand, each of the Okazaki fragments requires a new primer. As replication proceeds, these RNA primers are removed by the exonuclease activity of DNA polymerase I, and replaced with DNA nucleotides.
Finally, any remaining nicks between the newly synthesized DNA and the previously synthesized DNA are sealed by DNA ligase, ensuring the integrity of the DNA molecule.