how many hydrogen bonds form between g and c
GC-content The GC pair is bound by three hydrogen bonds, while AT and AU pairs are bound by two hydrogen bonds. To emphasize this difference in the number of hydrogen bonds, the base pairings can be represented as respectively Gâ‰¡C versus A=T and 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 stabilization, the stabilization is due mainly to interactions of base stacking.[2] In spite of the higher thermostability conferred to the genetic material, it has been observed that at least some bacteria species with DNA of high GC-content undergo autolysis more readily, thereby reducing the longevity of the cell per se.[3] Due to the thermostability given to the genetic materials in high GC organisms, it was commonly believed that the GC content played a necessary role in adaptation temperatures, a hypothesis that was refuted in 2001.[4] However, it has been shown that there is a strong correlation between the prokaryotic optimal growth at higher temperatures and the GC content of structured RNAs (such as ribosomal RNA, transfer RNA, and many other non-coding RNAs).[4][5] The AU base pairs are less stable than the GC base pairs previously attributed to GC bonds containing 3 hydrogen bonds and AU having only 2 hydrogen bonds, making high-GC-content RNA structures more resistant to the effects of high temperatures. More recently, it has been proved that the most stabilizing factor of 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 G:C pairs because of the relative positions of exocyclic groups than in the A:U pairs. Additionally, there is a correlation between the order in which the bases stack and thermal stability.[6]
Carbon–carbon bond A carbon–carbon bond is a covalent bond between two carbon atoms.[1] The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is formed between one hybridized orbital from each of the carbon atoms. In ethane, the orbitals are sp3-hybridized orbitals, but single bonds formed between carbon atoms with other hybridisations do occur (e.g. sp2 to sp2). In fact, the carbon atoms in the single bond need not be of the same hybridisation. Carbon atoms can also form double bonds in compounds called alkenes or triple bonds in compounds called alkynes. A double bond is formed with an sp2-hybridized orbital and a p-orbital that isn't involved in the hybridization. A triple bond is formed with an sp-hybridized orbital and two p-orbitals from each atom. The use of the p-orbitals forms a pi bond.