Primer: this is the initial terminus of a molecule onto which additional units are added to produce the final product. Most biological polymers are synthesized through an initial
addition to a primer system. In glycogen synthesis, the primer is small polysaccharide
made up of glucose units unto which glycosyl units are added. In fatty acids synthesis,
acetylacyl carrier protein (ACP) is the primer and malonylcoA, the adding unit. So also in
DNA replication, small polyribonucleotides are first formed with DNA as a template and
they then serve as primer for the addition of deoxyribonucleotide for the synthesis of
new DNA strands. A specific RNA polymerase called primase join the prepriming
complex to form a primeosome. The primase synthesise a short stretch of RNA 5-10
nucleotides that is complementary to one of the template DNA strand which is removed
at the end of replication by the 5’-3’ exonuclease activity of DNA polymerase I.