Intron: Difference between revisions

Latest revision as of 19:08, 22 March 2025

Non-coding sections of an RNA transcript

Intron[edit]

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.

Structure and Function[edit]

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.

Types of Introns[edit]

Introns can be classified into several types based on their splicing mechanisms:

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.

Nuclear pre-mRNA introns: These are the most common type of introns in eukaryotic cells and require the spliceosome for their removal.

tRNA introns: These are found in some tRNA genes and are removed by a different splicing mechanism involving specific endonucleases and ligases.

Role in Gene Expression[edit]

Introns play several important roles in gene expression and regulation:

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.

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.

Evolutionary Role: Introns may facilitate evolution by allowing for the recombination of exons, leading to the creation of new genes with novel functions.

Evolutionary Origin[edit]

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[edit]

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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:Molecular biology]]
-[[Category:Cell biology]]