Eukaryotic pre-mRNA processing | RNA splicing (article) | Khan Academy
Introns of nuclear genes have termination codons in all three reading frames. Intron - RNA sequences between exons that are removed by splicing The left end of the right intron/exon molecule forms a 5'-2' linkage to the adenosine in the . (see Table ). Terminal exons, at the beginning and end of mRNA transcripts, can be The first step in splicing is typically the ATP-independent recognition of the 5' 'The association of the U2 snRNP with the branch point regon is an ATP-. Splicing or RNA splicing is one of the post-transcriptional modifications steps for the removal of introns; it is the important process which is done.
We don't know for sure why splicing exists, and in some ways, it seems like a wasteful system. However, splicing does allow for a process called alternative splicing, in which more than one mRNA can be made from the same gene.
Through alternative splicing, we and other eukaryotes can sneakily encode more different proteins than we have genes in our DNA. In alternative splicing, one pre-mRNA may be spliced in either of two or sometimes many more than two! For example, in the diagram below, the same pre-mRNA can be spliced in three different ways, depending on which exons are kept.
This results in three different mature mRNAs, each of which translates into a protein with a different structure. Diagram of alternative splicing. Exon 1, Exon 2, Exon 3, Exon 4, and Exon 5. The exons are arranged in linear order along the pre-mRNA and have introns in between them. In splicing event 1, all five exons are retained in the mature mRNA. When it is translated, it specifies Protein A, a protein with five domains: In splicing event 2, Exon 3 is not included in the mature mRNA.
It consists of Exon 1 - Exon 2 - Exon 4 - Exon 5. When it is translated, it specifies Protein, B a protein with four domains: In splicing event 3, Exon 4 is not included in the mature mRNA. It consists of Exon 1 - Exon 2 - Exon 3 - Exon 5. When it is translated, it specifies Protein C, a protein with four domains: Professional biologists would like to know the answer too.
It's not totally clear why introns and splicing are so widespread in eukaryotes. So for this, the pre-mRNA undergoes the process called splicing.
Splicing or RNA splicing is one of the post-transcriptional modifications steps for the removal of introns; it is the important process which is done very precisely. This modification is supported by the small nuclear ribonucleoprotein particles snRNPs or snurps. Together they are called as the spliceosome. The snurps binds at both the ends of the intron and forms the loop, and then the intron is removed from the sequence, and the exons are joined together.
Post-transcriptional modifications occur in the nucleus, after which the mature RNA mRNA moves to the cytosol to perform the function of translation. Why is introns removal essential? As we discussed before, that introns are non-coding part of the nucleotide sequence as well as not highly conserved. So it is necessary to splice off or remove the introns to avoid the production of the wrong or incorrect protein.
As if any introns got left or any exon got deleted, all the faulty proteins will be produced.
Difference Between Introns and Exons
This occurs because the amino acids which make the proteins are based on the codons left over after the post-transcriptional modifications.
The three nucleotides present in the sequence, make up the amino acid and proceeds with protein production.
Definition of Exons Exons are the coding part of the nucleotide sequence, which encodes for the amino acid sequence for the protein. These are the only parts, which are transcribed and converted into mature mRNA after post-transcriptional modification.
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These further moved to the cytoplasm, where they are translated into proteins, this happens with the support of another molecule known as tRNA. Alternative splicing is helpful in promoting the different combinations of amino acids, by producing different combinations of exons and thus different proteins are formed.
Key Differences Between Introns and Exons Following points presents the significant differences between the two regions of the nucleotide sequence: Introns also are known as the intervening sequence, are known as the non-coding region of the nucleotide sequence and are present between the two exons.