View source for Biology:Nitrogenous base

[[Image:Adenine.svg|thumb|100px|right|Adenine]]
[[Image:Tymina.svg|thumb|100px|right|Thymine]]
[[Image:Guanin.svg|thumb|100px|right|Guanine]]
[[Image:Cytosine_chemical_structure.png|thumb|100px|right|Cytosine]]
[[Image:Uracil.svg|thumb|100px|right|Uracil]]

A '''nitrogenous base''', or [[Chemistry:Nitrogen|nitrogen]]-containing   [[Chemistry:Base|base]], is an organic molecule with a nitrogen [[Physics:Atom|atom]] that has the chemical properties of a base. The main biological function of a nitrogenous base is to [[Chemistry:Chemical bond|bond]] [[Biology:Nucleic acid|nucleic acid]]s together. A nitrogenous base owes its basic properties to the [[Chemistry:Lone pair|lone pair]] of [[Physics:Electron|electron]]s of a nitrogen atom.

Nitrogenous bases are typically classified as the derivatives of two parent compounds, [[Chemistry:Pyrimidine|pyrimidine]] and [[Chemistry:Purine|purine]].<ref>Nelson, David L. and Michael M Cox (2008). [https://archive.org/details/LehningersPrinciplesOfBiochemistry5e ''Lehninger Principles of Biochemistry''], ed. 5, W.H. Freeman and Company. p. 272. {{ISBN|071677108X}}.</ref> They are non-polar and due to their [[Chemistry:Aromaticity|aromaticity]], [[Physics:Trigonal planar molecular geometry|planar]]. Both pyrimidines and purines resemble [[Chemistry:Pyridine|pyridine]] and are thus weak bases and relatively unreactive towards [[Chemistry:Electrophilic aromatic substitution|electrophilic aromatic substitution]].<ref>Carey, Francis A. (2009). ''Organic Chemistry'', ed. 6, Mc Graw Hill. p. 1206. {{ISBN|0072828374}}.</ref>

==Role in nucleic acids==
{{Main|Biology:Nucleobase}}
In the biological sciences, nitrogenous bases are increasingly termed [[Biology:Nucleobase|nucleobase]]s because of their role in [[Biology:Nucleic acid|nucleic acid]]s - their flat shape is particularly important when considering their roles as the building blocks of [[Biology:DNA|DNA]] and [[Biology:RNA|RNA]]. A set of five nitrogenous bases is used in the construction of [[Biology:Nucleotide|nucleotide]]s, which in turn build up nucleic acids like DNA and RNA. These nitrogenous bases are [[Chemistry:Adenine|adenine]] (A), [[Chemistry:Uracil|uracil]] (U), [[Chemistry:Guanine|guanine]] (G), [[Chemistry:Thymine|thymine]] (T), and [[Chemistry:Cytosine|cytosine]] (C). 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.<ref name=":0">{{Citation|last=Soukup|first=Garrett A.|chapter=Nucleic Acids: General Properties|date=2003|publisher=American Cancer Society|language=en|doi=10.1038/npg.els.0001335|isbn=9780470015902|title=eLS}}</ref> The nitrogenous bases form [[Chemistry:Hydrogen bond|hydrogen bond]]s between opposing DNA strands to form the rungs of the "twisted ladder" or double helix of DNA or a biological catalyst that is found in the [[Biology:Nucleotide|nucleotide]]s. Adenine is always paired with thymine, and guanine is always paired with cytosine. These are known as [[Biology:Base pair|base pair]]s. Adenine forms two hydrogen bonds with thymine in DNA and two hydrogen bonds with uracil in RNA, while three hydrogen bonds are formed between guanine and cytosine. There are a variety of other non-canonical base pairs that occur in nature due to the versatility of these molecular structures.<ref name=":0" /> Uracil is only present in RNA, replacing thymine. [[Chemistry:Pyrimidine|Pyrimidine]]s include thymine, cytosine, and uracil. They have a single ring structure. [[Chemistry:Purine|Purine]]s include adenine and guanine. They have a double ring structure.<ref>Angstadt, Carol N (1997) [http://library.med.utah.edu/NetBiochem/pupyr/pp.htm Purine and Pyrimidine Metabolism]. library.med.utah.edu</ref>

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== References ==
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