Nucleic acid 21496 220528085 2008-06-20T08:40:23Z Rcej 1612789 pl {{for|a non-technical introduction to the topic|Introduction to genetics}} A '''nucleic acid''' is a [[macromolecule]] composed of chains of monomeric [[nucleotide]]s. In [[biochemistry]] these [[molecule]]s carry [[genetic information]] or form structures within [[Cell (biology)|cells]]. The most common nucleic acids are '''[[DNA|deoxyribonucleic acid]]''' (DNA) and '''[[RNA|ribonucleic acid]]''' (RNA). Nucleic acids are universal in living things, as they are found in all cells and [[virus]]es. Nucleic acid was first discovered by [[Friedrich Miescher]]. [[nucleic acid analogues|Artificial nucleic acids]] include '''[[peptide nucleic acid]]''' (PNA), '''[[Morpholino]]''' and '''[[locked nucleic acid]]''' (LNA), as well as '''[[GNA (nucleic acid)|glycol nucleic acid]]''' (GNA) and '''[[TNA (nucleic acid)|threose nucleic acid]]''' (TNA). Each of these is distinguished from naturally-occurring DNA or RNA by changes to the backbone of the molecule. ==Chemical structure== The term "nucleic acid" is the generic name for a family of [[biopolymer]]s, named for their role in the [[cell nucleus]]. The [[monomer]]s from which nucleic acids are constructed are called [[nucleotide]]s. Each nucleotide consists of three components: a nitrogenous [[heterocyclic]] [[base (chemistry)|base]], which is either a [[purine]] or a [[pyrimidine]]; a [[pentose]] [[sugar]]; and a [[phosphate]] group. Nucleic acid types differ in the structure of the sugar in their nucleotides - DNA contains 2-[[deoxyribose]]s while RNA contains [[ribose]] (where the only difference is the presence of a [[hydroxyl group]]). Also, the nitrogenous bases found in the two nucleic acid types are different: [[adenine]], [[cytosine]], and [[guanine]] are found in both RNA and DNA, while [[thymine]] only occurs in DNA and [[uracil]] only occurs in RNA. Other rare nucleic acid bases can occur, for example [[inosine]] in strands of mature [[transfer RNA]]. Nucleic acids are usually either single-stranded or double-stranded, though structures with three or more strands can form. A double-stranded nucleic acid consists of two single-stranded nucleic acids held together by [[chemical bond|hydrogen bonds]], such as in the DNA double helix. In contrast, RNA is usually single-stranded, but any given strand may fold back upon itself to form secondary structure as in tRNA and rRNA. Within cells, DNA is usually double-stranded, though some [[virus]]es have single-stranded DNA as their genome. [[Retrovirus]]es have single-stranded RNA as their genome. The sugars and phosphates in nucleic acids are connected to each other in an alternating chain, linked by shared oxygens, forming a [[Phosphodiester bonds|phosphodiester]] bond. In [[nucleic acid nomenclature|conventional nomenclature]], the carbons to which the phosphate groups attach are the 3' end and the 5' end carbons of the sugar. This gives nucleic acids polarity. The bases extend from a glycosidic linkage to the 1' carbon of the pentose sugar ring. Bases are joined through N-1 of pyrimidines and N-9 of purines to 1' carbon of ribose through N-β glycosyl bond. ==Types of nucleic acids== ===Ribonucleic acid=== :''Main article: [[RNA]]'' Ribonucleic acid, or RNA, is a nucleic acid polymer consisting of nucleotide monomers, which plays several important roles in the processes of translating genetic information from deoxyribonucleic acid (DNA) into proteins. RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes, forms vital portions of ribosomes, and serves as an essential carrier molecule for amino acids to be used in protein synthesis. ===Deoxyribonucleic acid=== :''Main article: [[DNA]]'' Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is the long-term storage of information and DNA is often compared to a set of blueprints, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. ==Nucleic acid components== ===Nucleobases=== :''Main article: [[Nucleobase]]'' Nucleobases are [[heterocyclic]] [[aromatic]] [[organic compound]]s containing [[nitrogen]] atoms. Nucleobases are the parts of [[RNA]] and [[DNA]] involved in [[base pair]]ing. [[Cytosine]], [[guanine]], [[adenine]], [[thymine]] are found predominantly in DNA, while in RNA [[uracil]] replaces [[thymine]]. These are abbreviated as C, G, A, T, U, respectively. Nucleobases are [[complementarity (molecular biology)|complementary]], and when forming base pairs, must always join accordingly: cytosine-guanine, adenine-thymine (adenine-uracil when RNA). The strength of the interaction between cytosine and guanine is stronger than between adenine and thymine because the former pair has three hydrogen bonds joining them while the latter pair have only two. Thus, the higher the GC content of double-stranded DNA, the more stable the molecule and the higher the [[DNA melting|melting]] temperature. Two main nucleobase classes exist, named for the molecule which forms their skeleton. These are the double-ringed [[purine]]s and single-ringed [[pyrimidine]]s. Adenine and guanine are purines (abbreviated as R), while cytosine, thymine, and uracil are all pyrimidines (abbreviated as Y). [[Hypoxanthine]] and [[xanthine]] are mutant forms of adenine and guanine, respectively, created through [[mutagen]] presence, through deamination (replacement of the amine-group with a hydroxyl-group). These are abbreviated HX and X. ===Nucleosides=== :''Main article: [[Nucleoside]]'' Nucleosides are [[glycosylamine]]s made by attaching a [[nucleobase]] (often referred to simply as bases) to a [[ribose]] or [[deoxyribose]] ([[sugar]]) ring. In short, a nucleoside is a base linked to sugar. The names derive from the nucleobase names. The nucleosides commonly occurring in DNA and RNA include [[cytidine]], [[uridine]], [[adenosine]], [[guanosine]] and [[thymidine]]. When a phosphate is added to a nucleoside (by [[phosphorylation|phosphorylated]] by a specific [[kinase]] enzyme), a nucleotide is produced. Nucleoside analogues, such as [[acyclovir]], are used as [[Nucleoside analogues|antiviral agents]]. ===Nucleotides and deoxynucleotides=== :''Main article: [[Nucleotide]]'' A nucleotide consists of a nucleoside and one or more [[phosphate]] [[Functional group|group]]s. Nucleotides are the [[monomers]] of [[RNA]] and [[DNA]], as well as forming the structural units of several important [[cofactor]]s - [[coenzyme A|CoA]], [[FAD|flavin adenine dinucleotide]], [[flavin mononucleotide]], [[adenosine triphosphate]] and [[nicotinamide adenine dinucleotide phosphate]]. In the [[cell (biology)|cell]] nucleotides play important roles in [[metabolism]], and signaling. Nucleotides are named after the nucleoside on which they are based, in conjunction with the number of phosphates they contain, for example: *Adenine bonded to ribose forms the nucleoside adenosine. *Adenosine bonded to a phosphate forms [[adenosine monophosphate]]. *As phosphates are added, [[adenosine diphosphate]] and [[adenosine triphosphate]] are formed, in sequence. ==See Also== *[[Nucleic acid methods]] ==External links== * [http://www.veaga.org.uk/video/programme/122 Interview with Aaron Klug, Nobel Laureate for structural elucidation of biologically important nucleic-acid protein complexes] provided by the Vega Science Trust. ==References== * Keith Roberts, Martin Raff, Bruce Alberts, Peter Walter, Julian Lewis and Alexander Johnson, ''Molecular Biology of the Cell'' 4th Edition, Routledge, March, 2002, hardcover, 1616 pages, 7.6 pounds, ISBN 0-8153-3218-1 {{Nucleic acids}} [[Category:Nucleic acids]] [[Category:Genetics]] [[bs:Nukleinske kiseline]] [[bg:Нуклеинова киселина]] [[ca:Àcid nucleic]] [[cs:Nukleová kyselina]] [[da:Nukleinsyre]] [[de:Nukleinsäuren]] [[el:Νουκλεϊκά οξέα]] [[es:Ácido nucleico]] [[eo:Nuklea acido]] [[eu:Azido nukleiko]] [[fa:اسید نوکلئیک]] [[fr:Acide nucléique]] [[gl:Ácido nucleico]] [[ko:핵산]] [[hr:Nukleinske kiseline]] [[id:Asam nukleat]] [[is:Kjarnsýra]] [[it:Acido nucleico]] [[he:חומצת גרעין]] [[lv:Nukleīnskābes]] [[lb:Nukleinsaier]] [[lt:Nukleino rūgštis]] [[mk:Нуклеинска киселина]] [[ms:Asid nukleik]] [[nl:Nucleïnezuur]] [[ja:核酸]] [[oc:Acid nucleïc]] [[pl:Kwasy nukleinowe]] [[pt:Ácido nucleico]] [[ro:Acid nucleic]] [[ru:Нуклеиновая кислота]] [[sq:Acidi nukleik]] [[simple:Nucleic acid]] [[sk:Nukleová kyselina]] [[sr:Нуклеинске киселине]] [[sh:Nukleinska kiselina]] [[su:Asam nukléat]] [[fi:Nukleiinihappo]] [[sv:Nukleinsyra]] [[th:กรดนิวคลีอิก]] [[vi:Axít nucleic]] [[tr:Nükleik asit]] [[uk:Нуклеїнові кислоти]] [[zh:核酸]]