Intron

Anintronis a non-coding sequence in agene.

It is anynucleotidesequence within agenethat is removed byRNA splicingto get the final RNA product of a gene.^[1]^[2]The termintronrefers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.^[3]

Sequences of coding DNA which are joined together in the final RNA after RNA splicing areexons. They code foramino acidsin the finalpolypeptide.

Introns are in the genes of most organisms and many viruses. They can be in a wide range of genes, including those that generateproteins,ribosomalRNA (rRNA), andtransfer RNA(tRNA). RNA splicing takes place aftertranscriptionand beforetranslation.

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 foramino-acidsequences in aprotein.

The discovery of introns led to theNobel Prize in Physiology or Medicinein 1993 forPhillip SharpandRichard Roberts.The termintronwas introduced by Americanbiochemist Walter Gilbert.^[4]

Biological meaning

There are many unanswered questions about introns. It is unclear whether introns serve some specific function, or whether they areselfish DNAwhich reproduces itself as aparasite.^[5]

Recent studies of entireeukaryotic genomeshave now shown that the lengths and density (introns/gene) of introns varies considerably between relatedspecies.There are four or five different kinds of intron. Some introns representmobile genetic elements(transposons).

Alternative splicingof introns within a gene allows a variety of proteinisoformsfrom 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.^[6]

References

↑Alberts, Bruce (2008).Molecular biology of the cell.New York: Garland Science.ISBN 978-0-8153-4105-5.
↑Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. (2007).Biochemistry.San Francisco: W.H. Freeman.ISBN 978-0-7167-6766-4.{{cite book}}:CS1 maint: multiple names: authors list (link)
↑Kinniburgh, Alan; Mertz J. and Ross J. (1978)."the precursor of mouse β-globin messenger RNA contains two intervening RNA sequences".Cell.14(3): 681–693.doi:10.1016/0092-8674(78)90251-9.PMID 688388.S2CID 21897383.{{cite journal}}:CS1 maint: multiple names: authors list (link)
↑Gilbert, Walter (1978). "Why genes in pieces".Nature.271(5645): 501.Bibcode:1978Natur.271..501G.doi:10.1038/271501a0.PMID 622185.S2CID 4216649.
↑Orgel L.E. & Crick, F.H.C. 1980. Selfish DNA: the ultimate parasite.Nature,284,604-607.
↑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 Genetics40(12): 1413–1415. doi:10.1038/ng.259.PMID 18978789.

[Alberts-1] Alberts, Bruce (2008).Molecular biology of the cell.New York: Garland Science.ISBN 978-0-8153-4105-5.

[Stryer-2] Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. (2007).Biochemistry.San Francisco: W.H. Freeman.ISBN 978-0-7167-6766-4.{{cite book}}:CS1 maint: multiple names: authors list (link)

[3] Kinniburgh, Alan; Mertz J. and Ross J. (1978)."the precursor of mouse β-globin messenger RNA contains two intervening RNA sequences".Cell.14(3): 681–693.doi:10.1016/0092-8674(78)90251-9.PMID 688388.S2CID 21897383.{{cite journal}}:CS1 maint: multiple names: authors list (link)

[4] Gilbert, Walter (1978). "Why genes in pieces".Nature.271(5645): 501.Bibcode:1978Natur.271..501G.doi:10.1038/271501a0.PMID 622185.S2CID 4216649.

[5] Orgel L.E. & Crick, F.H.C. 1980. Selfish DNA: the ultimate parasite.Nature,284,604-607.

[6] 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 Genetics40(12): 1413–1415. doi:10.1038/ng.259.PMID 18978789.

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