Introns are sections of DNA within a gene that do not encode part of the protein that the gene produces, and are splicing (genetics) out of the mRNA that is transcription from the gene before it is exported from the cell nucleus. Introns exist mainly (but not only) in eukaryote cell (biology). The regions of a gene that remain in the spliced mRNA are called exons. Introns sometimes allow for alternative splicing of a gene, so that several different proteins that share some sections in common can be produced from a single gene. The control of mRNA splicing, and hence of which alternative is produced, is performed by a wide variety of signal molecules. Introns also sometimes contain "old code," sections of a gene that were probably once translated into protein but which are now discarded. Some introns such as Group I and Group II introns are actually ribozymes that are capable of catalysis their own splicing out of the primary RNA transcript. They remove themselves on their own. The amount of intron DNA varies widely between species. The pufferfish species ''Fugu rubripes'' has a very low amount of intron DNA, whereas related species have higher amounts. Introns are not to be confused with junk DNA, which is all DNA without known function that is not part of a gene. ==Intron evolution== There are two competing theories as to the evolutionary origin of introns, which is usually studied in a highly conserved family of genes such as the actins. In the introns-early model ancestral genes are believed to have included a large number of introns, some of which have been lost over evolutionary time, leading to the different but similar intron patterns in related genes of different species. The introns-late model suggests instead that introns occur in the same location in variants of a given gene because the location is in some way predisposed to the introduction of an intron, and therefore that a similar intron pattern may arise in two different species by a form of convergent evolution. ==See also== *selfish DNA *noncoding DNA *intein ==Reference== #Walter Gilbert (1978 Feb 9) "Why Genes In Pieces?" ''Nature'' 271 (5645):501. Gene expression
This is cited as a piece of evidence in support of evolution. By whom? :By just about every book ever written on the subject, which you'd know if you ever care to read one. --LDC ::So, Great Master of intron science, please cite at least one if you know every book written on the subject... ::come one - am I right that you just copied this from a secondary source... Cf. dead code in most larger software systems... ---- "Junk DNA" is not a well-defined term, of course, but I would hesitate to say that it is ''synonymous'' with intron DNA. A lot of noncoding DNA that is never transcribed into RNA in the first place exists, and I believe that it is usually also considered to be "junk" DNA when factoids about how 90% or whatever of human DNA is junk are bandied about. user:Bryan Derksen :Good point. That should be stated within the article. There are in fact many types of non-junk DNA that are in fact vital to gene regulation and expression. So the statement you mention should read that "90% of all DNA does not code for any proteins". We might even want to have a separate article on this. :I wasn't trying to imply that the two terms were ''directly'' synonymous through the merge -- its just that the article at Junk DNA was mostly about Intron DNA. There is no reason not to have a separate article about the use of the term "junk DNA" while having intron keep to the technical facts. --user:maveric149
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Words begining with Intron:
Intron
Intron
Intronaut
Introns
Intron_DNA
Intron
Introns are sections of DNA within a gene that do not encode part of the protein that the gene produces, and are splicing (genetics) out of the mRNA that is transcription from the gene before it is exported from the cell nucleus. Introns exist mainly (but not only) in eukaryote cell (biology). The regions of a gene that remain in the spliced mRNA are called exons. Introns sometimes allow for alternative splicing of a gene, so that several different proteins that share some sections in common can be produced from a single gene. The control of mRNA splicing, and hence of which alternative is produced, is performed by a wide variety of signal molecules. Introns also sometimes contain "old code," sections of a gene that were probably once translated into protein but which are now discarded. Some introns such as Group I and Group II introns are actually ribozymes that are capable of catalysis their own splicing out of the primary RNA transcript. They remove themselves on their own. The amount of intron DNA varies widely between species. The pufferfish species ''Fugu rubripes'' has a very low amount of intron DNA, whereas related species have higher amounts. Introns are not to be confused with junk DNA, which is all DNA without known function that is not part of a gene. ==Intron evolution== There are two competing theories as to the evolutionary origin of introns, which is usually studied in a highly conserved family of genes such as the actins. In the introns-early model ancestral genes are believed to have included a large number of introns, some of which have been lost over evolutionary time, leading to the different but similar intron patterns in related genes of different species. The introns-late model suggests instead that introns occur in the same location in variants of a given gene because the location is in some way predisposed to the introduction of an intron, and therefore that a similar intron pattern may arise in two different species by a form of convergent evolution. ==See also== *selfish DNA *noncoding DNA *intein ==Reference== #Walter Gilbert (1978 Feb 9) "Why Genes In Pieces?" ''Nature'' 271 (5645):501. Gene expression
Intron
This is cited as a piece of evidence in support of evolution. By whom? :By just about every book ever written on the subject, which you'd know if you ever care to read one. --LDC ::So, Great Master of intron science, please cite at least one if you know every book written on the subject... ::come one - am I right that you just copied this from a secondary source... Cf. dead code in most larger software systems... ---- "Junk DNA" is not a well-defined term, of course, but I would hesitate to say that it is ''synonymous'' with intron DNA. A lot of noncoding DNA that is never transcribed into RNA in the first place exists, and I believe that it is usually also considered to be "junk" DNA when factoids about how 90% or whatever of human DNA is junk are bandied about. user:Bryan Derksen :Good point. That should be stated within the article. There are in fact many types of non-junk DNA that are in fact vital to gene regulation and expression. So the statement you mention should read that "90% of all DNA does not code for any proteins". We might even want to have a separate article on this. :I wasn't trying to imply that the two terms were ''directly'' synonymous through the merge -- its just that the article at Junk DNA was mostly about Intron DNA. There is no reason not to have a separate article about the use of the term "junk DNA" while having intron keep to the technical facts. --user:maveric149
See other meanings of words starting from letter:
I
IA | IB | IC | ID | IE | IF | IG | IH | IJ | IK | IL | IM | IN | IO | IP | IR | IS | IT | IU | IW | IX | IY | IZ |Words begining with Intron:
Intron
Intron
Intronaut
Introns
Intron_DNA
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