A primer is a component of the nucleic acid that serves as a starting point for DNA synthesis. They are necessary for the replication of DNA because the enzymes that catalyze DNA polymerases process only add new nucleotides to a strand of DNA exist. Polymerase replication starts at the 3'end of the primer, and copies the opposite strand.
In most cases replication of natural DNA, the primer for the synthesis of DNA replication and a short strand of RNA (which can be created de novo).
Many laboratory techniques of biochemistry and molecular biology that involve DNA polymerases, including DNA sequencing and polymerase chain reaction (PCR), DNA primers necessary. These primers are usually short, chemically synthesized oligonucleotides with a length of about twenty bases. They were hybridized with target DNA is then copied by the polymerase.