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A '''Ribonucleic acid''' (RNA) is a molecule found in all cells, comprised of many individual units of [[nucleic acid]].  It differs from DNA ([[deoxyribonucleic acid]]) in that it only contains a single, not double strand, and substitutes [[uracil]] for [[thymine]].  The sugar backbone of RNA is also composed of ribose (DNA contains deoxyribose). RNAs fall into several different categories, depending on function. 

'''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 RNA contains ribose instead of 2'-deoxyribose and uses [[uracil]] instead of [[thymine]] as one of its four bases.

The primary role of mRNA in is to transfer a copy of the information coded in DNA to a [[ribosome]] to be expressed as a protein, using a form of RNA known as messenger RNA ([[mRNA]]).  mRNA in eukaryotes undergoes spicing after transcription from DNA to remove [[introns]] or to use alternative splicing to create a different gene product. Alternatively-spliced transcripts can also express the same protein, but at different levels, due to the removal or addition of regulatory sequences.

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]]).

The main role of [[tRNA]], or transfer RNA is to carry an amino acid to the mRNA (while the mRNA is in the ribosome) during translation of the mRNA into a protein.

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.

 

The main role of [[rRNA]] or ribosomal RNA is to form the [[ribosome]].  RNA that has catalytic properties (such as the ribosome) is referred to as a [[ribozyme]].

 

Purification of RNA is problematic as enzymes that degrade RNA ([[RNases]]) are ubiquitous.  Successful RNA purification depends on degradation of the DNA template used via DNase and avoidance of RNase using sterile technique.

 

The polio virus is an example of an organism which contains only RNA to carry its genetic information. Some [[protists]] such as ''Paramecium'' carry similar RNA genes in structures called micronuclei. These are involved in mating and replicate independently from the main cell nucleus.

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