Editing GC-content (section)

==Structure==
Qualitatively, guanine (G) and cytosine (C) undergo a specific [[hydrogen bonding]] with each other, whereas adenine (A) bonds specifically with thymine (T) in DNA and with uracil (U) in RNA. Quantitatively, each GC [[base pair]] is held together by three hydrogen bonds, while AT and AU base pairs are held together by two hydrogen bonds. To emphasize this difference, the base pairings are often represented as "G≡C" versus "A=T" or "A=U".

DNA with low GC-content is less stable than DNA with high GC-content; however, the hydrogen bonds themselves do not have a particularly significant impact on molecular stability, which is instead caused mainly by molecular interactions of base stacking.<ref name ="Yakovchuk2006">{{cite journal |vauthors=Yakovchuk P, Protozanova E, Frank-Kamenetskii MD |title=Base-stacking and base-pairing contributions into thermal stability of the DNA double helix |journal=Nucleic Acids Res. |volume=34 |issue=2 |pages=564–74 |year=2006 |pmid=16449200 |pmc=1360284 |doi=10.1093/nar/gkj454 |url=}}</ref> In spite of the higher [[thermostability]] conferred to a nucleic acid with high GC-content, it has been observed that at least some species of [[bacteria]] with DNA of high GC-content undergo [[Autolysis (biology)|autolysis]] more readily, thereby reducing the longevity of the cell ''per se''.<ref>{{cite journal |vauthors=Levin RE, Van Sickle C |title=Autolysis of high-GC isolates of Pseudomonas putrefaciens |journal=Antonie van Leeuwenhoek |volume=42 |issue=1–2 |pages=145–55 |year=1976 |pmid=7999 |doi=10.1007/BF00399459 |s2cid=9960732 }}</ref> Because of the thermostability of GC pairs, it was once presumed that high GC-content was a necessary [[adaptation]] to high temperatures, but this hypothesis was refuted in 2001.<ref name="Hurst2001">{{cite journal |vauthors=Hurst LD, Merchant AR |title = High guanine-cytosine content is not an adaptation to high temperature: a comparative analysis amongst prokaryotes|journal = Proc. Biol. Sci.|volume = 268|issue = 1466|pages = 493–7|date = March 2001|pmid = 11296861|pmc = 1088632|doi = 10.1098/rspb.2000.1397}}</ref> Even so, it has been shown that there is a strong correlation between the optimal growth of [[prokaryote]]s at higher temperatures and the GC-content of structural RNAs such as [[ribosomal RNA]], [[transfer RNA]], and many other [[non-coding RNA]]s.<ref name="Hurst2001" /><ref>{{cite journal | last1=Galtier | first1=N. | last2=Lobry | first2=J.R. | title=Relationships between genomic G+C content, RNA secondary structures, and optimal growth temperature in Prokaryotes | journal=Journal of Molecular Evolution| volume=44 | pages=632–636 | year=1997 | pmid=9169555 | doi=10.1007/PL00006186 | issue=6 | bibcode=1997JMolE..44..632G| s2cid=19054315 }}</ref> The AU base pairs are less stable than the GC base pairs, making high-GC-content RNA structures more resistant to the effects of high temperatures.

More recently, it has been demonstrated that the most important factor contributing to the thermal stability of double-stranded nucleic acids is actually due to the base stackings of adjacent bases rather than the number of hydrogen bonds between the bases. There is more favorable stacking energy for GC pairs than for AT or AU pairs because of the relative positions of exocyclic groups. Additionally, there is a correlation between the order in which the bases stack and the thermal stability of the molecule as a whole.<ref>{{Cite journal|last1=Yakovchuk|first1=Peter|last2=Protozanova|first2=Ekaterina|last3=Frank-Kamenetskii|first3=Maxim D.|date=2006|title=Base-stacking and base-pairing contributions into thermal stability of the DNA double helix|journal=Nucleic Acids Research|volume=34|issue=2|pages=564–574|doi=10.1093/nar/gkj454|issn=0305-1048|pmc=1360284|pmid=16449200}}</ref>