Some basic principles need to be clarified. The direction of translation and transcription 5 to 3. Is every piece of DNA used only in one gene or can be used in more than one gene , I mean example a sequence of DNA (TGATCGCTCATCTC) at site X? of chromosome 1 . Can be part of gene X? and gene Y . Is the anti-sense side of the DNA also used as part of the genes ?
Guys, what is INTRON for one gene could be the ENHANCER or a DISTAL PROMOTER for another gene. In order words, intronic sequences for gene A could potentially harbor regulatory elements(enhancers , LCR etc) for gene B. Human alpha globin HS40 enhancer element is embedded within the intron of next gene. Further next gen Seq have proved beyond doubt that high transcriptional activities takes place in introns. microRNA, lcRNA, antisense RNA etc can be coded from the intronic region. So what we call useless intron for a particular gene maybe a treasure for another gene. Also lets not forget that intron provides the room for alternative splicing and producing transcript variants.
No one knows exactly why introns exist. One hypothesis proposes that introns make it possible to assemble genes from various exon building blocks that encode modules of protein function. This type of assembly would allow the shuffling of exons to make new genes, a process that appears to have played a key role in the evolution of complex organisms. The exon-as-module proposal is attractive because it is easy to understand the selective advantage of the potential for exon shuffling. Nevertheless, it remains a hypothesis without proof; SOURCE: (Names: Hartwell, Leland, author. Title: Genetics : from genes to genomes / Leland Hartwell, Michael Goldberg, Janice Fischer, Lee Hood, Charles F. Aquadro, Bruce Bejcek. Description: Sixth edition. ∣ New York, NY : McGraw-Hill Education, [2018])
One of the known benefit is that different organs in the same organism can make proteins that are tailored to their specific organ using the same gene. For example, suppose you have three exons A,B and C, separated by two introns. One organ may want a final m-RNA of ABC but another organ may want only AB. By having these intron breaks between exons it is then possible for organ specific spliceosomes to make either ABC or AB from the same gene. Thus the organs get the protein that suits them best. I've heard that introns could allow a single gene to make thousands of variations. So the loss of m-RNA production efficiency by inserting introns pays off in personalized proteins. As the Sioux warrior said in Dances with Wolves... good trade. Nature uses what is available so doubtlessly the introns have other "duties" that we have yet to discover.
They decrease the possibility of having mutations on exons which gonna be translated later into protiens plus they give you huge variation of protiens depending on how they gonna be cut
Guys, what is INTRON for one gene could be the ENHANCER or a DISTAL PROMOTER for another gene. In order words, intronic sequences for gene A could potentially harbor regulatory elements(enhancers , LCR etc) for gene B. Human alpha globin HS40 enhancer element is embedded within the intron of next gene. Further next gen Seq have proved beyond doubt that high transcriptional activities takes place in introns. microRNA, lcRNA, antisense RNA etc can be coded from the intronic region. So what we call useless intron for a particular gene maybe a treasure for another gene. Also lets not forget that intron provides the room for alternative splicing and producing transcript variants.
Hey I couldn't find this answer online so I actually had to read my textbook. 1) Splicing at different points allows you to translate variety of proteins from a single gene. (makes sense) 2) From a long-term evolution perspective. Being able to mix-and match your codons and splice certain regions and not others occasionally gives rise to new useful proteins. Apparently many of our proteins appear to have been made from a patchwork of pre-existing proteins. (also makes sense) When asking how we ended up with Introns but prokaryotes don't, there are two theories: A) All cells originally had Introns, but Prokaryotes dumped them because they need to be able to reproduce as quickly as possible and Introns slowed them down. B) Introns are the result of hundreds of millions of years of viruses adding their DNA to ours, and instead of removing it from our genome we just splice it out. Personally I think theory A is more credible.
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No one knows exactly why introns exist. One hypothesis proposes that introns make it possible to assemble genes from various exon building blocks that encode modules of protein function. This type of assembly would allow the shuffling of exons to make new genes, a process that appears to have played a key role in the evolution of complex organisms. The exon-as-module proposal is attractive because it is easy to understand the selective advantage of the potential for exon shuffling. Nevertheless, it remains a hypothesis without proof; SOURCE: (Names: Hartwell, Leland, author. Title: Genetics : from genes to genomes / Leland Hartwell, Michael Goldberg, Janice Fischer, Lee Hood, Charles F. Aquadro, Bruce Bejcek. Description: Sixth edition. ∣ New York, NY : McGraw-Hill Education, [2018])
Most introns • start with GU: (site splice donor) and • end with AG (site acceptor or receiver splicing) • The 5 'end of the intron binds to site adenosine connection.
So, if the mutation theory is correct, and eukaryotes evolved from prokaryotes as evolution insists, this means that introns AND spliceosomes had to occur simultaneously, by whimsical coincidence, be non-deadly, and also perfectly match in form so that the spliceosome could interact with the intron. If the spliceosome came first, it would be a disadvantage to the organism as this would waste resources and space. If the intron came first, rna could not be properly read.
A third possibility is that they were originally entangled in a primitive common mechanism that ultimately broke apart and spawned them both. My view of all these feedback systems is that their ancestors were more likely physically closer than they are now. This is an easier way to explain what is almost impossible to explain through serendipity. But then, I can imagine two chemicals that discover each other and form a symbiotic relationship. But there are so many chains of events in biochemistry that a more believable model is that they were once connected and the advantage of their being detached proved to be an evolutionary advantage. That is much more believable.
