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Reference.org
Non-coding RNA
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<p>A non-coding RNA (ncRNA) is a functional <a href="/facts/RNA/HxPeNfNj">RNA</a> molecule that is not <a href="/facts/Translation_(genetics)/JcPC1rth">translated</a> into a <a href="/facts/Protein/Jxmagu3E">protein</a>. The <a href="/facts/DNA/nB89Iauz">DNA</a> sequence from which a functional non-coding RNA is transcribed is often called an RNA <a href="/facts/Gene/e1swwPY6">gene</a>. Abundant and functionally important <a href="/facts/List_of_RNAs/8JnQgAMj">types of non-coding RNAs</a> include <a href="/facts/Transfer_RNA/pR9T5XSl">transfer RNAs</a> (tRNAs) and <a href="/facts/Ribosomal_RNA/zy5FxddY">ribosomal RNAs</a> (rRNAs), as well as small RNAs such as <a href="/facts/MicroRNA/UjqbYYpe">microRNAs</a>, <a href="/facts/SiRNA/891ytkD9">siRNAs</a>, <a href="/facts/PiRNA/5JXza7t8">piRNAs</a>, <a href="/facts/SnoRNA/lcWShLfJ">snoRNAs</a>, <a href="/facts/SnRNA/6XKVBBJM">snRNAs</a>, <a href="/facts/Extracellular_RNA/9WaEkf74">exRNAs</a>, <a href="/facts/ScaRNAs/fFP7Ta1u">scaRNAs</a> and the <a href="/facts/Long_noncoding_RNA/FHyAb6hP">long ncRNAs</a> such as <a href="/facts/Xist/GgcYIt15">Xist</a> and <a href="/facts/HOTAIR/j5oKl3WV">HOTAIR</a>. </p><p>The number of non-coding RNAs within the human genome is unknown; however, recent <a href="/facts/Transcriptomics/0ytdk54p">transcriptomic</a> and <a href="/facts/Bioinformatics/D5x2L8ee">bioinformatic</a> studies suggest that there are thousands of non-coding transcripts. Many of the newly identified ncRNAs have unknown functions, if any. There is no consensus on how much of non-coding transcription is functional: some believe most ncRNAs to be non-functional "junk RNA", spurious transcriptions, while others expect that many non-coding transcripts have functions to be discovered. </p>