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Post-transcriptional modification
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<p>Transcriptional modification or co-transcriptional modification is a set of biological processes common to most <a href="/facts/Eukaryote/SkwyPLMA">eukaryotic</a> cells by which an <a href="/facts/RNA/HxPeNfNj">RNA</a> <a href="/facts/Primary_transcript/4UXtKPHw">primary transcript</a> is chemically altered following <a href="/facts/Transcription_(biology)/bDgp9HDN">transcription</a> from a <a href="/facts/Gene/e1swwPY6">gene</a> to produce a mature, functional RNA molecule that can then leave the <a href="/facts/Cell_nucleus/D7sFRa3c">nucleus</a> and perform any of a variety of different functions in the cell. There are many types of post-transcriptional modifications achieved through a diverse class of molecular mechanisms. </p><p>One example is the conversion of precursor <a href="/facts/Messenger_RNA/oUL6qxQn">messenger RNA</a> transcripts into mature messenger RNA that is subsequently capable of being <a href="/facts/Translation_(biology)/JcPC1rth">translated</a> into <a href="/facts/Protein/Jxmagu3E">protein</a>. This process includes three major steps that significantly modify the chemical structure of the RNA molecule: the addition of a <a href="/facts/5%27_cap/cWUeEBJ6">5' cap</a>, the addition of a 3' <a href="/facts/Polyadenylation/ILnXUBKP">polyadenylated</a> tail, and <a href="/facts/RNA_splicing/a2QEvCRI">RNA splicing</a>. Such processing is vital for the correct translation of eukaryotic <a href="/facts/Genome/31Sm08JT">genomes</a> because the initial precursor mRNA produced by transcription often contains both <a href="/facts/Exon/8KWJtLuN">exons</a> (coding sequences) and <a href="/facts/Intron/LS6YdBEK">introns</a> (non-coding sequences); splicing removes the introns and links the exons directly, while the cap and tail facilitate the transport of the mRNA to a <a href="/facts/Ribosome/CF2u2gtg">ribosome</a> and protect it from molecular degradation. </p><p>Post-transcriptional modifications may also occur during the processing of other transcripts which ultimately become <a href="/facts/Transfer_RNA/pR9T5XSl">transfer RNA</a>, <a href="/facts/Ribosomal_RNA/zy5FxddY">ribosomal RNA</a>, or any of the other types of RNA used by the cell. </p>