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<p>A <b>non-coding RNA</b><span style="color: #000000"> (<b>ncRNA</b>) is a functional RNA molecule that is not translated into a protein. Less-frequently used synonyms are non-protein-coding RNA (npcRNA), non-messenger RNA (nmRNA), small non-messenger RNA (snmRNA) and functional RNA (fRNA). The term <b>small RNA</b> (<b>sRNA</b>) is often used for small bacterial ncRNAs. The DNA sequence from which a non-coding RNA is transcribed as the end product is often called an <b>RNA gene</b> or non-coding RNA gene.</span></p>

<p><span style="color: #000000">Non-coding RNA genes include highly abundant and functionally important RNAs such as transfer RNA (tRNA) and ribosomal RNA (rRNA), as well as RNAs such as snoRNAs, microRNAs, siRNAs and piRNAs and the long ncRNAs that include examples such as Xist and HOTAIR (see here for a more complete list of ncRNAs). The number of ncRNAs encoded within the human genome is unknown, however recent transcriptomic and bioinformatic studies suggest the existence of thousands of ncRNAs.<sup id="cite_ref-pmid15790807_0-0" class="reference"><font size="2">[1]</font></sup><sup id="cite_ref-pmid17571346_1-0" class="reference"><font size="2">[2]</font></sup><sup id="cite_ref-pmid17568003_2-0" class="reference"><font size="2">[3]</font></sup>^{<font size="2">, but see</font>} <sup id="cite_ref-3" class="reference"><font size="2">[4]</font></sup> Since many of the newly identified ncRNAs have not been validated for their function, it is possible that many are non-functional.<sup id="cite_ref-pmid15851066_4-0" class="reference"><font size="2">[5]</font></sup></span></p>

<h2><span style="color: #000000"><span id="History_and_discovery" class="mw-headline">History and discovery</span></span></h2>

<div class="rellink boilerplate further"><span style="color: #000000">Further information: History of molecular biology</span></div>

<p><span style="color: #000000">Nucleic acids were first discovered in 1868 by Friedrich Miescher<sup id="cite_ref-5" class="reference"><font size="2">[6]</font></sup> and by 1939 RNA had been implicated in protein synthesis.<sup id="cite_ref-6" class="reference"><font size="2">[7]</font></sup> Two decades later, Francis Crick predicted a functional RNA component which mediated translation; he reasoned that RNA is better suited to base-pair with the mRNA transcript than a pure polypeptide.<sup id="cite_ref-7" class="reference"><font size="2">[8]</font></sup></span></p>

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<span style="color: #000000">The cloverleaf structure of Yeast tRNA^{<font size="1">Phe</font>} (<i>inset</i>) and the 3D structure determined by X-ray analysis.</span></div>

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<h3><span style="color: #000000"><span id="ncRNAs_in_translation" class="mw-headline">ncRNAs in translation</span></span></h3>

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<span style="color: #000000">An illustration of the central dogma of molecular biology annotated with the processes ncRNAs are involved in. RNPs are shown in red, ncRNAs are shown in blue.</span></div>

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<span style="color: #000000">Atomic structure of the 50S Subunit from <i>Haloarcula marismortui</i>. Proteins are shown in blue and the two RNA strands in orange and yellow.<sup id="cite_ref-Ban_21-0" class="reference"><font size="1">[22]</font></sup> The small patch of green in the center of the subunit is the active site.</span></div>

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<h3><span style="color: #000000"><span id="ncRNAs_in_RNA_splicing" class="mw-headline">ncRNAs in RNA splicing</span></span></h3>

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<span style="color: #000000">Electron microscopy images of the yeast spliceosome. Note the bulk of the complex is in fact ncRNA.</span></div>

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<h2><span id="External_links" class="mw-headline">External links</span></h2>

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