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A 'nucleic acid' is a macromolecule made from nucleotide chains. In biochemistry these molecules can convey genetic information or form structures within cells. The most common nucleic acids are 'deoxyribonucleic acid' (DNA) and 'ribonucleic acid' (RNA). Nucleic acids are universal in living things as they are found in all cells and viruses.
Artificial nucleic acids include 'peptide nucleic acid' (PNA), 'Morpholino' and 'locked nucleic acid' (LNA), as well as 'glycol nucleic acid' (GNA) and 'threose nucleic acid' (TNA). Each of these is distinguished from naturally-occurring DNA or RNA by changes to the backbone of the molecule.

Contents

Chemical structure

Types of nucleic acids

Nucleobases

Nucleosides

Nucleotides and deoxynucleotides

Ribonucleic acids

Deoxyribonucleic acids

External links

Chemical structure

The term "nucleic acid" is the generic name of a family of biopolymers, named for their role in a cell nucleus. The monomers from which nucleic acids are constructed are called nucleotides. Each nucleotide consists of three components: a nitrogenous heterocyclic base, which is either a purine or a pyrimidine; a pentose sugar; and a phosphate group. Different nucleic acid types differ in the structure of the sugar in their nucleotides - DNA contains 2-deoxyriboses while RNA contains ribose. Likewise, the nitrogenous bases found in the two nucleic acids are different: adenine, cytosine, and guanine are 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 hydrogen-bonded together, 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 double-helical regions. Within cells, DNA is usually double-stranded, though some viruses have single-stranded DNA 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 functional group. In conventional nomenclature, the carbons to which the phosphate groups are attached are the 3' and the 5' carbons of the sugar. The bases extend from a glycosidic linkage to the 1' carbon of the pentose sugar ring.

Types of nucleic acids

Nucleobases

:''Main article: Nucleobase''
Nucleobases are heterocyclic aromatic organic compounds containing nitrogen atoms. Nucleobases are the parts of RNA and DNA involved in base pairing. Cytosine, guanine, adenine, thymine are the found predominantly in DNA, while in RNA uracil replaces thymine. These are abbreviated as C, G, A, T, U, respectively.
Two main classes exist, named for the molecule which forms their skeleton. These are the double-ringed purines and single-ringed pyrimidines. 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 glycosylamines 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 phosphorylated by a specific kinase enzyme), a nucleotide is produced.

Nucleotides and deoxynucleotides

:''Main article: Nucleotide''
A nucleotide consists of a nucleoside and one or more phosphate groups. Nucleotides are the monomers of RNA and DNA, as well as forming the structural units of several important cofactors - CoA, flavin adenine dinucleotide, flavin mononucleotide, adenosine triphosphate and nicotinamide adenine dinucleotide phosphate. In the 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.

Ribonucleic acids

:''Main article: RNA''

Deoxyribonucleic acids

:''Main article: DNA''

External links

★ Prediction of hairpin forming potential in nucleotide sequences

★ Interview with Aaron Klug, Nobel Laureate for structural elucidation of biologically important nucleic-acid protein complexes provided by the Vega Science Trust.