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Why do we have introns and what is the purpose of them? Why do we waste...

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Biology

Why do we have introns and what is the purpose of them?

Why do we waste energy making introns?

The question may be broad but it's something our professor askedus. Thank you.

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4.1 Ratings (594 Votes)
Introns The two major divisions of DNA that are transcribed into RNA are proteincoding sections called exons and nonproteincoding sections called introns Introns consist of large stretches of DNA whose biological functions are only beginning to be elucidated The mRNA was eventually found to be shorter because it lacked the noncoding sequences introns between the coding regions the exons on the DNA7 It was discovered that introns were normally removed by splicing enzymes before mRNA messenger RNA rRNA ribosomal RNA and tRNA transfer RNA can complete their functions in the cell Because introns interrupt the nucleotide sequences they first were called interrupted genes The int in intron refers to intervening because introns always exist between exons In eukaryotes intron removal and splicing is completed within the nucleus Sequences that code for protein are called exons because they travel exit outside the nucleus to code for proteins and thus are the DNA sequences that are expressed the prefix ex in the term exon is from expressed The Process of Removing Introns Shows Evidence of Design When mRNA is transcribed from DNA both the exon and intron noncoding sequences are transcribed into a macromolecule known as a heterogeneous nuclear RNA hnRNA or immature RNA Before the RNA exits the nucleus the introns must be removed by a precise cleavageligation reaction called splicing thereby producing a functional mRNA Enzymes and small ribonucleoprotein structures exist in all eukaryotic cells to assist in removing introns In most cases type I introns are removed in the nucleus by a complex splicing machine composed of small nuclear ribonuclear proteins SNRP SNRPs consist of 60300 small nuclear RNA snRNA nucleotides in an intimate alliance with a bouquet of proteins The process of intron removal involves a precise looping process controlled by a specific nucleotide sequence that abuts the exonsAlmost all known introns are identified by specific consensus sequences GT at the start or donor3 end and AG at the other end called the acceptor 5 site which help to identify introns for removal The term consensus sequence is employed because although the sites may consist of more than just GT donor and AG acceptor bases so far as is known these sequences are common to all eukaryotic organisms Consensus sequences are DNA segments that use similar base sequences in different genes within a single gene family or across many different species for one specific function After the introns are cut out the exon RNA is spliced back together by RNA ligase so that the final mRNA used to code polypeptides normally consists only of exons In Type II introns RNA itself functions as an enzyme called a riboenzyme or ribozyme These enzymes require a divalent cation usually magnesium to function The process of removing introns involves a complicated reaction pathway that includes RNA intermediates called lariats branch connecting points and a large number of accessory proteins Roles of Introns in the Cell Indications that introns have a use include the observation that the cell puts a huge amount of its energy into the creation of these introns then discards them Nature would not go to all that trouble without a reasonWhy most genes of higher organisms are broken up into short exons separated by huge stretches of seemingly useless DNA is particularly puzzling because the introns are all painfully transcribed into RNA only to be snipped out by snRNPs and thrown away almost immediatelyEvolutionist Patrusky says Nature for reasons as yet unknown created the intron and evolution has chosen to keep it and ultimately has found new ways to use it An important finding which may help researchers to understand the role of introns is the more primitive and simple the organism generally the fewer the introns Although the majority of plant and animal genomes have not yet been examined introns have been found in the vast majority of eukaryotic genes and likely exist in    See Answer
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