Final answer:
DNA polymerases need a primer with a free 3'-OH end, synthesized by RNA primase, to initiate DNA synthesis.
Step-by-step explanation:
All DNA polymerases require a primer providing a free 3'-OH end to initiate DNA synthesis. This primer is synthesized by an enzyme known as RNA primase. The primer is a short complementary sequence of RNA nucleotides that bonds with the template strand of DNA. The DNA polymerase is then able to add DNA nucleotides to this primer, extending the DNA molecule during replication. While extending the leading strand requires only one primer, the lagging strand requires multiple primers for the synthesis of Okazaki fragments. Ultimately, these RNA primers are replaced by DNA nucleotides, and the gaps filled by DNA polymerase I. Any remaining nicks are sealed by DNA ligase, which creates a continuous DNA strand by forming phosphodiester linkages.