Primer

A primer marks the starting point for the synthesis of DNA. They are made of nucleic acid strands. Primers are necessary for the process of DNA replication. This is because DNA polymerase cannot create new strands of DNA, It can only add to existing strands of DNA. The primer acts as the preexisting strand which allows DNA Polymerase to begin it's synthesis (1).

Primers exist naturally but can also be chemically synthesized. Laboratory techniques including Polymerase Chain Reactions and DNA sequencing require the chemical synthesis of oligonucleotides to act as primers (1). Oligonucleotide primers can be customized which is significant because a primer will only bind to the region of DNA that is it's compliment. This is what allows researches to amplify very specific sections of DNA. Chemically synthesized oligonucleotides are generally between fifteen and twenty bases in length. The length of the primer limits the number of sequences that can be added to the primer (2).

References:
 * 1) Primer (molecular biology). (2015, March 28). Retrieved from http://en.wikipedia.org/wiki/Primer_(molecular_biology)
 * 2) Explanation of Oligonucleotide Synthesis. (2003, January 1). Retrieved from http://www.bio.davidson.edu/Courses/Molbio/MolStudents/spring2003/Holmberg/oligonucleotide_synthesis.htm