Prab at 11:32, 31 August 2023

2023-08-31T11:32:24Z

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'''RNA''', or '''ribonucleic acid''', is a [[nucleic acid]] responsible for various cellular functions, differing from its more well-known counterpart, [[DNA]]. RNA molecules are distinct in both structure and function and come in various forms with unique roles in the cell.<ref>Only the most important are described here. A complete list is available at [[:en:List of RNAs]].</ref>
[[File:RNA basic structure.JPG|RNA_basic_structure|thumb]] [[File:RNA Editing.png|RNA_Editing|thumb]] [[File:Schematic of RNA timestamp workflow, 4 steps.png|Schematic_of_RNA_timestamp_workflow,_4_steps|thumb]] [[File:RNA pol.jpg|RNA_pol|thumb]]
== Overview ==

Unlike [[DNA]], which consists of two intertwined strands forming a double helix, RNA is typically single-stranded. It incorporates the following [[Nucleotide|bases]]:

* :(A) [[Adenine]]
* :(G) [[Guanine]]
* :(C) [[Cytosine]]
* :(U) [[Uracil]]

These bases allow for specific pairings: adenine (A) with uracil (U), and guanine (G) with cytosine (C). Notably, RNA uses [[uracil]] in place of the [[thymine]] found in DNA.

Another significant difference between RNA and DNA is the sugar component. RNA molecules contain [[ribose]], whereas DNA contains [[deoxyribose]]. The presence of ribose renders RNA more chemically reactive than DNA, equipping it to participate actively in cellular reactions.

In specific [[virus|viruses]], particularly [[retrovirus|retroviruses]] like [[HIV]], RNA carries genetic information, deviating from the common rule where DNA is the primary genetic material.

== Protein synthesis RNAs ==

RNA's primary role is facilitating protein synthesis. It conveys the amino acid sequence information from genes to [[ribosomes]] in the [[cytoplasm]], where proteins are assembled.

=== Messenger RNA ===
[[File:MRNA structure.svg|thumb|650px|center|The structure of a mature eukaryotic mRNA. A fully processed mRNA includes a [[5' cap]], [[5' UTR]], [[coding region]], [[3' UTR]], and poly(A) tail. UTR = untranslated region]]

'''[[messenger RNA]]''' (mRNA) is responsible for this information transfer. A DNA strand serves as a template for mRNA transcription, which is facilitated by the [[enzyme]] [[RNA polymerase]]. Once transcribed, the mRNA moves from the [[nucleus]] to the [[ribosomes]] in the cytoplasm. Here, mRNA's sequence of bases dictates the sequence of [[amino acids]] in the protein synthesis, a process called [[Translation (genetics)|translation]].

While DNA remains in the nucleus due to its considerable size and its association with proteins like [[histone]]s in [[chromosome]]s, mRNA is mobile and can interact with various cellular enzymes.

Non-coding RNAs, including transfer RNA (tRNA) and ribosomal RNA (rRNA), assist in protein synthesis.

=== tRNA ===
[[Transfer RNA]] (tRNA) is approximately 80 [[nucleotide]]s in length and delivers specific amino acids to the growing polypeptide chain on a [[ribosome]]. Different tRNAs correspond to different amino acids, each having a unique attachment site for its respective amino acid and an anti-codon matching the mRNA's codon. For instance, the codons UUU or UUC denote the amino acid [[phenylalanine]].

=== rRNA ===
'''Ribosomal RNA''' (rRNA) forms the primary component of ribosomes, cellular machinery where protein synthesis takes place. In eukaryotes, there are four rRNA molecules: 18S, 5.8S, 28S, and 5S rRNA. Three of these are synthesized in the [[nucleolus]], while the fourth is created elsewhere. In the cytoplasm, the rRNA and proteins combine to form ribosomes, which, by binding mRNA, facilitate protein synthesis. Several ribosomes can attach to a single mRNA simultaneously.<ref name=The_Cell>{{cite book | title=The Cell: a molecular approach| edition=3rd| author=Cooper GC & Hausman RE| date=2004| pages=261–76, 297, 339–44| publisher=Sinauer| isbn=0-87893-214-3 | oclc=174924833 52121379 52359301 56050609}}</ref> rRNA is abundant and constitutes about 80% of the 10 mg/ml RNA in a typical eukaryotic [[cytoplasm]].<ref>{{cite journal | author=Kampers T. et al. | title=RNA stimulates aggregation of microtubule-associated protein tau into Alzheimer-like paired helical filaments| journal=FEBS Letters| year=1996| volume=399 | pages = 104D| pmid=8985176 | doi = 10.1016/S0014-5793(96)01386-5 | issue=3}}</ref>

=== snRNAs ===
[[Small nuclear RNA]]s (snRNA) combine with proteins to form [[spliceosome]]s, which control [[alternative splicing]]. Genes encode proteins in segments known as [[exon]]s. These can be combined in various ways to produce different mRNAs, allowing multiple proteins to originate from a single gene. Unwanted protein versions are degraded by [[protease]]s, with their components recycled.

== Regulatory RNAs ==

Some RNAs play a role in gene regulation, modulating the rate of gene transcription or translation.<ref name=Morris>{{cite book |chapterurl=http://www.horizonpress.com/rnareg|author= Morris KV|year=2008|chapter=|title=RNA and the regulation of gene expression: a hidden layer of complexity|publisher=Caister Academic Press|id= ISBN 978-1-904455-25-7}}</ref> [[MicroRNAs]] and [[small interfering RNAs]] are examples. These molecules are instrumental in RNA interference (RNAi), a mechanism responsible for silencing gene expression.

== RNA Processing ==

After transcription, eukaryotic mRNAs undergo several modifications before they can function in the cytoplasm. These processes, collectively termed RNA processing, include 5' capping, 3' [[polyadenylation]], and [[RNA splicing]].<ref>{{cite journal | author=Sharp PA| title=The centrality of RNA| journal=Cell |year=2009| volume=136| pages=577–80| pmid=19239883| doi=10.1016/j.cell.2009.02.007}}</ref>

== RNA viruses ==

Certain viruses utilize RNA instead of DNA as their genetic material. These [[RNA virus]]es include [[HIV]], [[Ebola]], and the [[coronavirus]] family, like [[SARS-CoV-2]]. These viruses can be further classified based on their genomic structure and replication mechanisms.

== Applications and relevance ==

Research into RNA's structure and function has led to crucial developments in biotechnology and medicine. [[RNA interference]] technology, for instance, shows promise in gene regulation and therapeutic applications.<ref>{{cite journal | author=David Baulcombe| title=RNA silencing| journal=Trends in Biochemical Sciences|year=2004| volume=29| pages=418–24| pmid=15276190| doi=10.1016/j.tibs.2004.06.006}}</ref>

[[RNA vaccine]]s, which use a small piece of an RNA molecule to trigger an immune response, have become particularly relevant in the face of the [[COVID-19 pandemic]], with the approval and deployment of the [[Pfizer-BioNTech COVID-19 vaccine]] and the [[Moderna COVID-19 vaccine]].

== See also ==

* [[DNA]]
* [[Protein synthesis]]
* [[RNA world hypothesis]]
* [[RNA interference]]
* [[RNA splicing]]
* [[Transcription (genetics)]]
* [[Translation (genetics)]]
== References ==

<references />
== External links ==

* [http://www.rna-society.org/ The RNA Society]
* [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mboc4&part=A7444 RNA - The Versatile Molecule]
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[[Category:Cell biology]]

RNA - Revision history

Prab at 11:32, 31 August 2023