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Across all eukaryotic genes in GenBank, there were (in 2002), on average, 5.48 exons per protein coding gene. The average exon encoded 30-36 amino acids. [7] While the longest exon in the human genome is 11555 bp long, several exons have been found to be only 2 bp long. [8] A single-nucleotide exon has been reported from the Arabidopsis genome. [9]
Exon shuffling is a molecular mechanism for the formation of new genes. It is a process through which two or more exons from different genes can be brought together ectopically , or the same exon can be duplicated , to create a new exon-intron structure. [ 1 ]
The genomic fragment is inserted into the intron of a 'splicing vector' consisting of a known exon - intron - exon sequence of DNA, and the vector is then inserted into an eukaryotic cell. If the fragment does not contain exons (i.e., consists solely of intron DNA), it will be spliced out together with the vector's original intron.
During the process of splicing, an RNA-protein catalytical complex known as spliceosome catalyzes two transesterification reactions, which remove an intron and release it in form of lariat structure, and then splice neighbouring exons together. [11] In certain cases, some introns or exons can be either removed or retained in mature mRNA. [12]
The split gene theory is a theory of the origin of introns, long non-coding sequences in eukaryotic genes between the exons. [1] [2] [3] The theory holds that the randomness of primordial DNA sequences would only permit small (< 600bp) open reading frames (ORFs), and that important intron structures and regulatory sequences are derived from stop codons.
This results in a mature messenger RNA with a missing section of an exon. In this way, a point mutation, which might otherwise affect only a single amino acid, can manifest as a deletion or truncation in the final protein. [citation needed] Intron Exon Boundary in pre-mRNA 1 - 3' Splice site 2 - Poly pyrimidine Tract 3 - Branch site 4 - 5 ...
An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word intron is derived from the term intragenic region, i.e., a region inside a gene. [1] The term intron refers to both the DNA sequence within a gene and the corresponding RNA sequence in RNA transcripts. [2]
A minigene is a minimal gene fragment that includes an exon and the control regions necessary for the gene to express itself in the same way as a wild type gene fragment. This is a minigene in its most basic sense. More complex minigenes can be constructed containing multiple exons and intron(s).