primer

A primer is a short nucleic acid sequence that provides a starting point for DNA synthesis. In living organisms, primers are short strands of RNA. A primer must be synthesized by an enzyme called primase, which is a type of RNA polymerase, before DNA replication can occur. The synthesis of a primer is necessary because the enzymes that synthesize DNA, which are called DNA polymerases, can only attach new DNA nucleotides to an existing strand of nucleotides. The primer therefore serves to prime and lay a foundation for DNA synthesis. The primers are removed before DNA replication is complete, and the gaps in the sequence are filled in with DNA by DNA polymerases. In the laboratory, scientists can design and synthesize DNA primers with specific sequences that bind to sequences in a single-stranded DNA molecule. These DNA primers are commonly used to perform the polymerase chain reaction to copy pieces of DNA or for DNA sequencing.