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'''Ribonucleic acid''' (RNA) is a family of biomolecules which perform several essential functions within all cells.  As a type of nucleic acid, RNA is structurally and chemically very similar to [[DNA]]; the two largest differences being that the RNA backbone contains ribose instead of 2'-deoxyribose and uses [[uracil]] instead of [[thymine]] as one of its four bases<ref>Nelson & Cox. (2008). ''Principles of biochemistry''.</ref>.

'''Ribonucleic acid''' (RNA) is a family of biomolecules which perform several essential functions within all cells.  As a type of nucleic acid, RNA is structurally and chemically very similar to [[DNA]]; the two largest differences being that the RNA backbone contains ribose instead of 2'-deoxyribose and uses [[uracil]] instead of [[thymine]] as one of its four bases.<ref>Nelson & Cox. (2008). ''Principles of biochemistry''.</ref>

Unlike DNA, which is primarily used as a template for [[transcription]], RNA molecules perform a diverse set of functions within the cell.  Subsets of RNA are generally classified by their function, which can range from acting as the template for [[translation|protein synthesis]] ("messenger RNA" or "[[mRNA]]") to performing [[ribozyme|enzymatic functions]].  Additionally, many viruses use RNA instead of DNA as their genetic material (e.g. [[retrovirus|retroviruses]]).

Unlike DNA, which is primarily used as a template for [[transcription]], RNA molecules perform a diverse set of functions within the cell.  Subsets of RNA are generally classified by their function, which can range from acting as the template for [[translation|protein synthesis]] ("messenger RNA" or "[[mRNA]]") to performing [[ribozyme|enzymatic functions]].  Additionally, many viruses use RNA instead of DNA as their genetic material (e.g. [[retrovirus]]es).

As with DNA, RNAs can exist in single-stranded (annotated "ssRNA") or double-stranded ("dsRNA") forms; however, the vast majority of cellular RNAs are single-stranded.  dsRNAs generally function in post-transcriptional [[gene regulation]] or as viral genetic material.  Targeted degradation of dsRNAs is a major intracellular defence mechanism against viruses<ref>Alberts et al. (2008). ''Molecular biology of the cell''.</ref><ref>Weaver, Robert F. ''Molecular Biology''. 4th ed. Boston: McGraw-Hill, 2008.</ref>.

As with DNA, RNAs can exist in single-stranded (annotated "ssRNA") or double-stranded ("dsRNA") forms; however, the vast majority of cellular RNAs are single-stranded.  dsRNAs generally function in post-transcriptional [[gene regulation]] or as viral genetic material.  Targeted degradation of dsRNAs is a major intracellular defence mechanism against viruses.<ref>Alberts et al. (2008). ''Molecular biology of the cell''.</ref><ref>Weaver, Robert F. ''Molecular Biology''. 4th ed. Boston: McGraw-Hill, 2008.</ref>

==Structure==

==Structure==

Every nucleotide of RNA consists of a ribose molecule with a nitrogenous base attached to its 1' carbon and a phosphate group attached to its 5' carbon.  Individual RNA nucleotides are linked by a [[phosphodiester bond]] between the 3' carbon of one nucleotide's ribose and the 5' carbon on the next.

Every nucleotide of RNA consists of a ribose molecule with a nitrogenous base attached to its 1' carbon and a phosphate group attached to its 5' carbon.  Individual RNA nucleotides are linked by a [[phosphodiester bond]] between the 3' carbon of one nucleotide's ribose and the 5' carbon on the next.

The four nitrogenous bases used in RNA are [[adenine]], [[guanine]], [[cytosine]], and [[uracil]].  Adenine and guanine are the ''purine'' bases, cytosine and uracil are the ''pyrimidine'' bases.  Like in DNA, these bases can hybridize through [[hydrogen bond|hydrogen bonds]]; adenine hybridizes with uracil and guanine hybridizes cytosine.

The four nitrogenous bases used in RNA are [[adenine]], [[guanine]], [[cytosine]], and [[uracil]].  Adenine and guanine are the ''purine'' bases, cytosine and uracil are the ''pyrimidine'' bases.  Like in DNA, these bases can hybridize through [[hydrogen bond]]s; adenine hybridizes with uracil and guanine hybridizes cytosine.

Hybridization of nucleotides within RNA molecules allows for the formation of ''secondary structures'' such as RNA hairpins, these secondary structures give RNA molecules an overall ''tertiary structure'' which is often essential for the RNA to perform its function.  Additionally, RNAs can hybridize through base pairing with other RNAs or with complementary DNA sequences.

Hybridization of nucleotides within RNA molecules allows for the formation of ''secondary structures'' such as RNA hairpins, these secondary structures give RNA molecules an overall ''tertiary structure'' which is often essential for the RNA to perform its function.  Additionally, RNAs can hybridize through base pairing with other RNAs or with complementary DNA sequences.

===mRNA===

===mRNA===

''Messenger RNAs'' ([[mRNA]]) are the template molecules which are ''translated'' into [[protein|proteins]] by [[ribosome|ribosomes]].  They are generally synthesized by [[transcription]] of a DNA template (a [[gene]]) by [[RNA polymerase]], although some viral mRNAs are directly transcribed from an RNA template.

''Messenger RNAs'' ([[mRNA]]) are the template molecules which are ''translated'' into [[protein]]s by [[ribosome]]s.  They are generally synthesized by [[transcription]] of a DNA template (a [[gene]]) by [[RNA polymerase]], although some viral mRNAs are directly transcribed from an RNA template.

In [[eukaryote|eukaryotes]], nascent RNA transcripts must generally be processed from ''pre-mRNA'' into mature mRNA, via ''RNA processing'', before they are exported from the nucleus to be translated into proteins.

In [[eukaryote]]s, nascent RNA transcripts must generally be processed from ''pre-mRNA'' into mature mRNA, via ''RNA processing'', before they are exported from the nucleus to be translated into proteins.

===rRNA===

===rRNA===

''Ribosomal RNAs'' ([[rRNA]]) are the RNA molecules that form a major component of the [[ribosome|ribosomes]].  There are three rRNAs in [[prokaryote|prokaryotes]] and four rRNAs in [[eukaryote|eukaryotes]] and [[archaea|archaeans]].

''Ribosomal RNAs'' ([[rRNA]]) are the RNA molecules that form a major component of the [[ribosome]]s.  There are three rRNAs in [[prokaryote]]s and four rRNAs in [[eukaryote]]s and [[archaea]]ns.

The genes encoding rRNAs are among the most highly conserved (low level of sequence variance between individuals and species) genes in any genome.  As such, rRNA sequences are often used to generate very precise phylogenetic trees.

The genes encoding rRNAs are among the most highly conserved (low level of sequence variance between individuals and species) genes in any genome.  As such, rRNA sequences are often used to generate very precise phylogenetic trees.

===snRNA===

===snRNA===

''Small nuclear RNAs'' ([[snRNA]]) are involved in several different processes that occur within the nucleus, notably [[RNA splicing]] and the regulation of certain [[transcription factor|transcription factors]].  They generally function in complexes with specific proteins; these snRNA and protein complexes are called ''small nuclear ribonucleoproteins'' ("snRNPs", colloquially pronounced "snurps").

''Small nuclear RNAs'' ([[snRNA]]) are involved in several different processes that occur within the nucleus, notably [[RNA splicing]] and the regulation of certain [[transcription factor]]s.  They generally function in complexes with specific proteins; these snRNA and protein complexes are called ''small nuclear ribonucleoproteins'' ("snRNPs", colloquially pronounced "snurps").

==References==

==References==