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	~~An '''intron''' is a non~~-coding ~~sequence in a [[gene]].~~		{{Short description\|Non-coding sections of an RNA transcript}}
			{{For\|the protein\|Intron (protein)}}

	It is ~~any~~ [[~~nucleotide~~]] ~~sequence within a~~ [[~~gene~~]] that is removed by [[RNA splicing]] ~~to get~~ the ~~final RNA product of a gene.<ref name="Alberts">{{cite book \|author=Alberts, Bruce \|title=Molecular biology~~ of the ~~cell \|publisher=Garland Science \|location=New York \|year=2008 \|pages= \|isbn=0~~-~~8153-4105-9 \|oclc= \|doi= \|accessdate=}}</ref><ref name="Stryer">{{cite book \|author=Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. \|title=Biochemistry \|publisher=W~~.H. Freeman \|location=San Francisco \|year=2007 \|pages= \|isbn=0-7167-6766-X \|oclc= \|doi= \|accessdate=}}</ref> The term ''intron'' refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.<ref>{{cite journal\|last=Kinniburgh\|first=Alan\|coauthors=Mertz J. and Ross J.\|title=the Precursor of mouse β-globin messenger RNA contains two intervening RNA sequences\|journal=Cell\|date=July 1978\|volume= 14\|issue=3\|pages=681-693\|url=http://www.cell.com/abstract/0092-8674(78)90251-9#}}</ref>		==Intron==
			An '''intron''' is a segment of a [[DNA]] or [[RNA]] molecule that does not code for proteins and interrupts the sequence of genes. Introns are found in the genes of most organisms and are removed by [[RNA splicing]] during the processing of the [[pre-mRNA]] into [[mature mRNA]].

	[[~~File:Pre-mRNA to mRNA~~.~~svg\|center\|thumb\|420px\|A~~ [[~~spliceosome~~]] ~~removes~~ introns ~~from~~ a [[~~Transcription (genetics)\|transcribed~~]] ~~pre-~~[[mRNA]] ~~segment (top)~~. This is called 'splicing~~'. After the introns have been removed (bottom)~~, the ~~mature mRNA sequence is ready for~~ [[~~Translation (genetics)\|translation~~]].]]		==Structure and Function==
			Introns are non-coding regions interspersed within the coding regions, or [[exons]], of a gene. During the process of [[transcription]], both introns and exons are transcribed into a [[pre-mRNA]] molecule. However, before the [[mRNA]] can be translated into a protein, the introns must be removed. This removal is accomplished through a process called [[RNA splicing]], which is carried out by a complex known as the [[spliceosome]].

	~~Sequences~~ of ~~coding DNA which are joined together in the final RNA after RNA~~ splicing ~~are '''exon'''s. They code for [[amino acid]]s in the final [[polypeptide]].~~		===Types of Introns===
			Introns can be classified into several types based on their splicing mechanisms:

	~~Introns~~ are in the ~~genes of most organisms and many viruses. They can be in a wide range of genes, including those that generate~~ [[~~protein~~]]s, [[~~Ribosome\|ribosomal~~]] ~~RNA (rRNA)~~, ~~and~~ [[~~transfer RNA]] (tRNA). RNA splicing takes place after [[Transcription (genetics)\|transcription~~]] and ~~before~~ [[~~Translation (genetics)\|translation~~]].		* '''Group I and Group II introns''': These are self-splicing introns that can catalyze their own removal without the need for additional proteins or [[RNA]] molecules. Group I introns are found in some [[rRNA]] genes, while Group II introns are found in [[mitochondrial]] and [[chloroplast]] genes.

	*~~Introns: parts of a gene which are discarded: non~~-~~working bits.~~		* '''Nuclear pre-mRNA introns''': These are the most common type of introns in [[eukaryotic]] cells and require the spliceosome for their removal.
	*Exons: ~~parts of a gene which~~ are ~~expressed: bits~~ of ~~a gene which code for [[amino-acid]] sequences~~ in a [[~~protein~~]].

	~~The discovery of~~ introns ~~led to the [[Nobel Prize in Physiology or Medicine]] in 1993 for [[Phillip Sharp]] and [[Richard Roberts]]. The term~~ ''~~intron~~'~~' was introduced by American~~ [[~~biochemist~~]] ~~[[Walter Gilbert]].<ref>{{cite journal~~		* '''tRNA introns''': These are found in some [[tRNA]] genes and are removed by a different splicing mechanism involving specific endonucleases and ligases.
	~~\|author=Gilbert, Walter \|authorlink=\|year=1978 \|title=Why~~ genes ~~in pieces \|journal=Nature \|volume=271 \|issue=5645 \|pages=501 \|doi=10~~.~~1038/271501a0 \|pmid=622185}}</ref>~~

	== ~~Biological meaning~~ ==		==Role in Gene Expression==
	There are many unanswered questions about introns. It is unclear whether introns serve some specific function, or whether they are [[selfish DNA]] which reproduces itself as a [[parasite]].<ref>Orgel L.E. & Crick, F.H.C. 1980. Selfish DNA: ~~the ultimate parasite. ''Nature'', '''284''', 604-607.</ref>~~		Introns play several important roles in gene expression and regulation:

	~~Recent studies of entire~~ [[~~eukaryote\|eukaryotic~~]] [[~~genome~~]]~~s have now shown that the lengths and density (introns/~~gene~~) of introns varies considerably between related [[species]]~~. ~~There are four or five different kinds~~ of ~~intron. Some introns represent [[mobile genetic element]]s ([[transposon]]s)~~.		* '''Alternative Splicing''': Introns allow for [[alternative splicing]], a process by which different combinations of exons are joined together to produce multiple [[protein]] variants from a single gene. This increases the diversity of proteins that can be produced by an organism.

	~~[[Alternative splicing]]~~ of ~~introns within a gene allows a variety~~ of ~~protein [[isoform]]s from a single~~ gene. ~~Thus multiple related proteins~~ can ~~be generated from a single gene and a single precursor mRNA transcript. The control~~ of ~~alternative RNA splicing is performed by complex network of signalling molecules. In humans~~, ~~~95%~~ of ~~genes with more than one exon are alternatively spliced.<ref>Pan~~, ~~Q; Shai O, Lee LJ, Frey BJ, Blencowe BJ 2008. Deep surveying~~ of ~~alternative splicing complexity in the human transcriptome by high-throughput sequencing. ''Nature Genetics'' '''40''' (12): 1413–1415. doi:10.1038/ng.259. PMID 18978789~~.~~</ref>~~		* '''Regulation of Gene Expression''': Introns can contain regulatory elements that influence the expression of the gene. These elements can affect the rate of transcription, the stability of the mRNA, and the efficiency of translation.

	== ~~References~~ ==		* '''Evolutionary Role''': Introns may facilitate [[evolution]] by allowing for the recombination of exons, leading to the creation of new genes with novel functions.
	~~{{Reflist}}~~
			==Evolutionary Origin==
			The origin of introns is a subject of ongoing research and debate. Two main hypotheses have been proposed:

			* '''Introns-early hypothesis''': Suggests that introns were present in the earliest forms of life and have been lost in many [[prokaryotic]] lineages.

			* '''Introns-late hypothesis''': Proposes that introns were inserted into genes after the divergence of prokaryotes and eukaryotes.

			==Related Pages==
			* [[Exon]]
			* [[RNA splicing]]
			* [[Alternative splicing]]
			* [[Gene expression]]
			* [[Protein synthesis]]

	[[Category:Genetics]]		[[Category:Genetics]]
	[[Category:Molecular biology]]		[[Category:Molecular biology]]
	~~[[Category:Cell biology]]~~

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2019-10-01T13:37:45Z

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An '''intron''' is a non-coding sequence in a [[gene]].

It is any [[nucleotide]] sequence within a [[gene]] that is removed by [[RNA splicing]] to get the final RNA product of a gene.<ref name="Alberts">{{cite book |author=Alberts, Bruce |title=Molecular biology of the cell |publisher=Garland Science |location=New York |year=2008 |pages= |isbn=0-8153-4105-9 |oclc= |doi= |accessdate=}}</ref><ref name="Stryer">{{cite book |author=Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. |title=Biochemistry |publisher=W.H. Freeman |location=San Francisco |year=2007 |pages= |isbn=0-7167-6766-X |oclc= |doi= |accessdate=}}</ref> The term ''intron'' refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.<ref>{{cite journal|last=Kinniburgh|first=Alan|coauthors=Mertz J. and Ross J.|title=the Precursor of mouse β-globin messenger RNA contains two intervening RNA sequences|journal=Cell|date=July 1978|volume= 14|issue=3|pages=681-693|url=http://www.cell.com/abstract/0092-8674(78)90251-9#}}</ref>

[[File:Pre-mRNA to mRNA.svg|center|thumb|420px|A [[spliceosome]] removes introns from a [[Transcription (genetics)|transcribed]] pre-[[mRNA]] segment (top). This is called 'splicing'. After the introns have been removed (bottom), the mature mRNA sequence is ready for [[Translation (genetics)|translation]].]]

Sequences of coding DNA which are joined together in the final RNA after RNA splicing are '''exon'''s. They code for [[amino acid]]s in the final [[polypeptide]].

Introns are in the genes of most organisms and many viruses. They can be in a wide range of genes, including those that generate [[protein]]s, [[Ribosome|ribosomal]] RNA (rRNA), and [[transfer RNA]] (tRNA). RNA splicing takes place after [[Transcription (genetics)|transcription]] and before [[Translation (genetics)|translation]].

*Introns: parts of a gene which are discarded: non-working bits.
*Exons: parts of a gene which are expressed: bits of a gene which code for [[amino-acid]] sequences in a [[protein]].

The discovery of introns led to the [[Nobel Prize in Physiology or Medicine]] in 1993 for [[Phillip Sharp]] and [[Richard Roberts]]. The term ''intron'' was introduced by American [[biochemist]] [[Walter Gilbert]].<ref>{{cite journal
|author=Gilbert, Walter |authorlink=|year=1978 |title=Why genes in pieces |journal=Nature |volume=271 |issue=5645 |pages=501 |doi=10.1038/271501a0 |pmid=622185}}</ref>

== Biological meaning ==
There are many unanswered questions about introns. It is unclear whether introns serve some specific function, or whether they are [[selfish DNA]] which reproduces itself as a [[parasite]].<ref>Orgel L.E. & Crick, F.H.C. 1980. Selfish DNA: the ultimate parasite. ''Nature'', '''284''', 604-607.</ref>

Recent studies of entire [[eukaryote|eukaryotic]] [[genome]]s have now shown that the lengths and density (introns/gene) of introns varies considerably between related [[species]]. There are four or five different kinds of intron. Some introns represent [[mobile genetic element]]s ([[transposon]]s).

[[Alternative splicing]] of introns within a gene allows a variety of protein [[isoform]]s from a single gene. Thus multiple related proteins can be generated from a single gene and a single precursor mRNA transcript. The control of alternative RNA splicing is performed by complex network of signalling molecules. In humans, ~95% of genes with more than one exon are alternatively spliced.<ref>Pan, Q; Shai O, Lee LJ, Frey BJ, Blencowe BJ 2008. Deep surveying of alternative splicing complexity in the human transcriptome by high-throughput sequencing. ''Nature Genetics'' '''40''' (12): 1413–1415. doi:10.1038/ng.259. PMID 18978789.</ref>

== References ==
{{Reflist}}

[[Category:Genetics]]
[[Category:Molecular biology]]
[[Category:Cell biology]]

Intron - Revision history

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