### GC content

The GC content is the ratio of guanines and cytosines among all nucleotides of a primer. The GC content is typically restricted to lie between 40% and 60%. GC-pairings are electrostatically more favorable than the pairings of other nucleotides, because guanine-cytosine interactions are based on three hydrogen bonds rather than two. Hence, the ratio of GCs is linked to the stability of the DNA-DNA duplex formed between primers and templates. Primers with balanced GC contents ensure balanced binding stabilities in the form of similar melting temperatures.

Primers with high GC contents have high melting temperatures, which may yield less product. Primers with low GC contents, have low melting temperatures and might effect unspecific binding.