Editing RNA (section)

===Differences between DNA and RNA===
[[File:50S-subunit of the ribosome 3CC2.png|thumb|Three-dimensional representation of the [[50S]] ribosomal subunit. Ribosomal RNA is in brown, proteins in blue. The active site is a small segment of rRNA, indicated in red.]]

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The chemical structure of RNA is very similar to that of [[DNA]], but differs in three primary ways:
* Unlike double-stranded DNA, RNA is usually a single-stranded molecule (ssRNA)<ref name="University of Utah-2015">{{cite web | url=https://learn.genetics.utah.edu/content/basics/rna/ | title =RNA: The Versatile Molecule | publisher =[[University of Utah]] | year =2015}}</ref> in many of its biological roles and consists of much shorter chains of nucleotides.<ref>{{cite web | url=http://www.chem.ucla.edu/harding/notes/notes_14C_nucacids.pdf | title=Nucleotides and Nucleic Acids | publisher=[[University of California, Los Angeles]] | access-date=2015-08-26 | archive-url=https://web.archive.org/web/20150923202511/http://www.chem.ucla.edu/harding/notes/notes_14C_nucacids.pdf | archive-date=2015-09-23 | url-status=dead }}</ref> However, [[RNA#Double-stranded RNA|double-stranded RNA]] (dsRNA) can form and (moreover) a single RNA molecule can, by complementary base pairing, form intrastrand double helixes, as in [[Transfer RNA|tRNA]].
* While the sugar-phosphate "backbone" of DNA contains ''[[deoxyribose]]'', RNA contains ''[[ribose]]'' instead.<ref>{{cite book | url =https://books.google.com/books?id=7-UKCgAAQBAJ&q=dna+contains+deoxyribose+rna+ribose&pg=PT386 | title =Analysis of Chromosomes | vauthors =Shukla RN | isbn =978-93-84568-17-7 | date =2014 | publisher =Agrotech Press }}{{Dead link|date=February 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Ribose has a [[Hydroxy group|hydroxyl]] group attached to the pentose ring in the [[nucleic acid nomenclature|2']] position, whereas deoxyribose does not. The hydroxyl groups in the ribose backbone make RNA more chemically [[Lability|labile]] than DNA by lowering the [[activation energy]] of [[hydrolysis]].
* The complementary base to [[adenine]] in DNA is [[thymine]], whereas in RNA, it is [[uracil]], which is an [[methylation|unmethylated]] form of thymine.<ref name=Biochemistry/>
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Like DNA, most biologically active RNAs, including [[mRNA]], [[tRNA]], [[rRNA]], [[snRNA]]s, and other [[non-coding RNA]]s, contain self-complementary sequences that allow parts of the RNA to fold<ref>{{cite journal | vauthors = Tinoco I, Bustamante C | title = How RNA folds | journal = Journal of Molecular Biology | volume = 293 | issue = 2 | pages = 271–81 | date = October 1999 | pmid = 10550208 | doi = 10.1006/jmbi.1999.3001 }}</ref> and pair with itself to form double helices. Analysis of these RNAs has revealed that they are highly structured. Unlike DNA, their structures do not consist of long double helices, but rather collections of short helices packed together into structures akin to proteins.

In this fashion, RNAs can achieve chemical [[catalysis]] (like enzymes).<ref>{{cite journal | vauthors = Higgs PG | title = RNA secondary structure: physical and computational aspects | journal = Quarterly Reviews of Biophysics | volume = 33 | issue = 3 | pages = 199–253 | date = August 2000 | pmid = 11191843 | doi = 10.1017/S0033583500003620 | s2cid = 37230785 }}</ref> For instance, determination of the structure of the ribosome—an [[Ribonucleoprotein|RNA-protein complex]] that catalyzes the assembly of proteins—revealed that its active site is composed entirely of RNA.<ref name=ribosome_activity>{{cite journal | vauthors = Nissen P, Hansen J, Ban N, Moore PB, Steitz TA | title = The structural basis of ribosome activity in peptide bond synthesis | journal = Science | volume = 289 | issue = 5481 | pages = 920–30 | date = August 2000 | pmid = 10937990 | doi = 10.1126/science.289.5481.920 | bibcode = 2000Sci...289..920N }}</ref>

[[File:RNA chemical structure.GIF|class=skin-invert-image|thumb|left|Structure of a fragment of an RNA, showing a guanosyl subunit]]
An important structural component of RNA that distinguishes it from DNA is the presence of a [[hydroxyl]] group at the 2' position of the [[Ribose|ribose sugar]]. The presence of this functional group causes the helix to mostly take the [[A-DNA|A-form geometry]],<ref>{{cite journal |vauthors=Salazar M, Fedoroff OY, Miller JM, Ribeiro NS, Reid BR | title = The DNA strand in DNA.RNA hybrid duplexes is neither B-form nor A-form in solution | journal = Biochemistry | volume = 32 | issue = 16 | pages = 4207–15 | date = April 1993 | pmid = 7682844 | doi = 10.1021/bi00067a007 }}</ref> although in single strand dinucleotide contexts, RNA can rarely also adopt the B-form most commonly observed in DNA.<ref>{{cite journal | vauthors = Sedova A, Banavali NK | title = RNA approaches the B-form in stacked single strand dinucleotide contexts | journal = Biopolymers | volume = 105 | issue = 2 | pages = 65–82 | date = February 2016 | pmid = 26443416 | doi = 10.1002/bip.22750 | s2cid = 35949700 }}</ref>  The A-form geometry results in a very deep and narrow major groove and a shallow and wide minor groove.<ref>{{cite journal | vauthors = Hermann T, Patel DJ | title = RNA bulges as architectural and recognition motifs | journal = Structure | volume = 8 | issue = 3 | pages = R47–54 | date = March 2000 | pmid = 10745015 | doi = 10.1016/S0969-2126(00)00110-6 | doi-access = free }}</ref> A second consequence of the presence of the 2'-hydroxyl group is that in conformationally flexible regions of an RNA molecule (that is, not involved in formation of a double helix), it can chemically attack the adjacent phosphodiester bond to cleave the backbone.<ref>{{cite journal | vauthors = Mikkola S, Stenman E, Nurmi K, Yousefi-Salakdeh E, Strömberg R, Lönnberg H | title = The mechanism of the metal ion promoted cleavage of RNA phosphodiester bonds involves a general acid catalysis by the metal aquo ion on the departure of the leaving group|journal=Journal of the Chemical Society, Perkin Transactions 2|date=1999|pages=1619–26|doi=10.1039/a903691a|issue=8}}</ref>