Global InformationNucleotide bases information
Nucleotide bases[1] (also nucleobases, nitrogenous bases) are nitrogen-containing biological compounds that form nucleosides, which, in turn, are components of nucleotides, with all of these monomers constituting the basic building blocks of nucleic acids. The ability of nucleobases to form base pairs and to stack one upon another leads directly to long-chain helical structures such as ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Five nucleobases—adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U)—are called primary or canonical. They function as the fundamental units of the genetic code, with the bases A, G, C, and T being found in DNA while A, G, C, and U are found in RNA. Thymine and uracil are distinguished by merely the presence or absence of a methyl group on the fifth carbon (C5) of these heterocyclic six-membered rings.[2][page needed] In addition, some viruses have aminoadenine (Z) instead of adenine. It differs in having an extra amine group, creating a more stable bond to thymine.[3]
Adenine and guanine have a fused-ring skeletal structure derived of purine, hence they are called purine bases.[4] The purine nitrogenous bases are characterized by their single amino group (−NH2), at the C6 carbon in adenine and C2 in guanine.[5] Similarly, the simple-ring structure of cytosine, uracil, and thymine is derived of pyrimidine, so those three bases are called the pyrimidine bases.[6]
Each of the base pairs in a typical double-helix DNA comprises a purine and a pyrimidine: either an A paired with a T or a C paired with a G. These purine-pyrimidine pairs, which are called base complements, connect the two strands of the helix and are often compared to the rungs of a ladder. Only pairing purine with pyrimidine ensures a constant width for the DNA. The A–T pairing is based on two hydrogen bonds, while the C–G pairing is based on three. In both cases, the hydrogen bonds are between the amine and carbonyl groups on the complementary bases.
Nucleobases such as adenine, guanine, xanthine, hypoxanthine, purine, 2,6-diaminopurine, and 6,8-diaminopurine may have formed in outer space as well as on earth.[7][8][9]
The origin of the term base reflects these compounds' chemical properties in acid–base reactions, but those properties are not especially important for understanding most of the biological functions of nucleobases.
- ^ The International Union of Pure and Applied Chemistry (IUPAC). "IUPAC - nucleotide bases (N04254)". goldbook.iupac.org.
- ^ Soukup, Garrett A. (2003). "Nucleic Acids: General Properties". eLS. American Cancer Society. doi:10.1038/npg.els.0001335. ISBN 9780470015902.
- ^ "Some viruses thwart bacterial defenses with a unique genetic alphabet". 5 May 2021.
- ^ The International Union of Pure and Applied Chemistry (IUPAC). "IUPAC - purine bases (P04953)". goldbook.iupac.org. doi:10.1351/goldbook.p04953.
- ^ Berg JM, Tymoczko JL, Stryer L. "Section 25.2, Purine Bases Can Be Synthesized de Novo or Recycled by Salvage Pathways". Biochemistry. 5th Edition. Retrieved 11 December 2019.
- ^ The International Union of Pure and Applied Chemistry (IUPAC). "IUPAC - pyrimidine bases (P04958)". goldbook.iupac.org. doi:10.1351/goldbook.p04958.
- ^ Callahan MP, Smith KE, Cleaves HJ, Ruzicka J, Stern JC, Glavin DP, House CH, Dworkin JP (August 2011). "Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases". Proceedings of the National Academy of Sciences of the United States of America. 108 (34). PNAS: 13995–8. Bibcode:2011PNAS..10813995C. doi:10.1073/pnas.1106493108. PMC 3161613. PMID 21836052.
- ^ Steigerwald, John (8 August 2011). "NASA Researchers: DNA Building Blocks Can Be Made in Space". NASA. Retrieved 10 August 2011.
- ^ ScienceDaily Staff (9 August 2011). "DNA Building Blocks Can Be Made in Space, NASA Evidence Suggests". ScienceDaily. Retrieved 9 August 2011.