What is the role of primers in DNA replication?

Primers are short RNA sequences (about 10 nucleotides) synthesized by primase that provide a free 3'-OH group for DNA polymerase to begin synthesis. DNA polymerase cannot initiate new strand synthesis de novo and can only add nucleotides to an existing 3' end. On the leading strand, only one primer is needed, while the lagging strand requires multiple primers for each Okazaki fragment. After DNA synthesis, primers are removed by RNase H or DNA polymerase I and replaced with DNA by repair mechanisms.