RNA splicing

RNA splicing is a crucial process in molecular biology that occurs during the expression of genes in eukaryotic organisms. It is the removal of introns (non-coding regions) and the joining of exons (coding regions) in the pre-mRNA (pre-messenger RNA) molecule to produce mature mRNA (messenger RNA).

Here's how RNA splicing works:

1. Transcription: The process begins with the transcription of a gene's DNA sequence into pre-mRNA by an enzyme called RNA polymerase. During transcription, both exons and introns are transcribed.

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3. Intron Removal: In the pre-mRNA molecule, introns are interspersed between exons. The introns do not code for proteins, so they need to be removed to form a functional mRNA. Small nuclear ribonucleoproteins (snRNPs) and other protein complexes recognize specific sequences at the boundaries of introns called splice sites.

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5. Spliceosome Formation: The splice sites are recognized by the spliceosome, a large molecular complex composed of snRNPs and additional proteins. The spliceosome assembles at the intron-exon junctions.

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7. Splicing: The spliceosome catalyzes the splicing reactions. It cuts the pre-mRNA at the 5' end of the intron, creating a branched structure called a lariat, with the intron forming a loop. Then, the spliceosome cuts the pre-mRNA at the 3' end of the intron, releasing the intron as a lariat structure.

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9. Exon Joining: The exons that are now free from the intron are ligated (joined) together, resulting in a continuous mature mRNA sequence that contains only exons.

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11. Mature mRNA: The mature mRNA molecule contains the genetic information that will be used during translation (protein synthesis) in the cytoplasm. It exits the nucleus and moves to the ribosomes, where it serves as a template for the assembly of amino acids into a specific protein.

RNA splicing allows for the generation of multiple protein isoforms from a single gene, a process known as alternative splicing. This alternative splicing greatly increases the diversity of proteins that can be produced from the limited number of genes in the genome, playing a significant role in the complexity and functionality of eukaryotic organisms.