Molecular biology / genomics · BEGINNER LESSON
Primer
A primer is a short nucleic acid sequence, usually DNA in the lab and RNA in living cells, that gives DNA polymerase a starting point for making DNA. In polymerase chain reaction (PCR), two primers define the DNA region that will be copied.
What a primer is
A primer is a short sequence of nucleic acid. In genomics and laboratory work, it is usually a short single-stranded DNA fragment that binds to a matching DNA sequence. In living organisms, primers are short RNA strands that help begin DNA replication. A nucleic acid is the molecule family that includes DNA and RNA; DNA polymerase is the enzyme that adds new DNA building blocks but cannot start a strand from nothing. [0,1,2]
[1] Primer - National Human Genome Research Institute (NHGRI) [2] primer [3] primer | NIST - National Institute of Standards and Technology
What it measures or defines in the lab
In PCR, a pair of primers hybridizes, meaning each primer sticks to a complementary sequence on the sample DNA. The pair brackets the region of interest, so that region is the part that gets amplified, or copied many times. Primers are also used in DNA sequencing and other experimental processes to target a particular sequence. [0,1,2]
[1] Primer - National Human Genome Research Institute (NHGRI) [2] primer [3] primer | NIST - National Institute of Standards and Technology
How it works
Primers work because they provide an existing end for DNA polymerase to extend. In cells, an enzyme called primase makes an RNA primer first; later the primer is removed and the gap is filled with DNA. In the lab, scientists can synthesize DNA primers with chosen sequences so they bind to a specific target. [1,2,0]
[2] primer [3] primer | NIST - National Institute of Standards and Technology [1] Primer - National Human Genome Research Institute (NHGRI)
Limits and practical details
Primers must match the target sequence well enough to bind where intended, so sequence choice matters. The sources note that primers are short, often about 18 to 30 bases long, and are designed to target a specific region. They do not themselves copy DNA; they only make copying possible for enzymes that do the synthesis. [0,2,1]
[1] Primer - National Human Genome Research Institute (NHGRI) [3] primer | NIST - National Institute of Standards and Technology [2] primer
SEE THE IDEA
How a primer helps DNA copying
Short DNA or RNA piece with a matching sequence
The stretch of DNA the primer binds to
Enzyme that extends from the primer
The bracketed segment that gets amplified or replicated
Primer binds target DNA, which lets DNA polymerase start copying the chosen region.
A primer is the starting piece that marks where DNA synthesis begins.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.