GC-content

GC-content (or guanine-cytosine content), in molecular biology, is the percentage of nitrogenous bases on a DNA molecule which are either guanine or cytosine (from a possibility of four different ones, also including adenine and thymine). This may refer to a specific fragment of DNA or RNA, or that of the whole genome. When it refers to a fragment of the genetic material, it may denote the GC-content of part of a gene (domain), single gene, group of genes (or gene clusters) or even a non-coding region. G (guanine) and C (cytosine) undergo a specific hydrogen bonding whereas A (adenine) bonds specifically with T (thymine). The GC pair is bound by three hydrogen bonds and AT paired by two hydrogen bonds, and thus GC pairs are more thermostable compared to the AT pairs. In spite of the higher thermostability conferred to the genetic material, it is envisaged that cells with high GC DNA undergo autolysis, thereby reducing the longitivity of the cell per se.Due to the robustness endowed to the genetic materials in high GC organisms it was commonly believed that the GC content played a vital part in adaptation temperatures, an hypothesis which has recently been refuted.
In PCR experiments, the GC-content of primers are used to determine their annealing temperature to the template DNA. A higher GC-content level indicates a higher melting temperature.