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Transcription (biology)
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<p>Transcription is the process of copying a segment of <a href="/facts/DNA/nB89Iauz">DNA</a> into <a href="/facts/RNA/HxPeNfNj">RNA</a> for the purpose of <a href="/facts/Gene_expression/alCPohLR">gene expression</a>. Some segments of DNA are transcribed into RNA molecules that can encode <a href="/facts/Protein/Jxmagu3E">proteins</a>, called <a href="/facts/Messenger_RNA/oUL6qxQn">messenger RNA</a> (mRNA). Other segments of DNA are transcribed into RNA molecules called <a href="/facts/Non-coding_RNA/aXqyV5so">non-coding RNAs</a> (ncRNAs). </p><p>Both DNA and RNA are <a href="/facts/Nucleic_acid/2tTgcI0v">nucleic acids</a>, which use <a href="/facts/Base_pair/xmPpPQ9W">base pairs</a> of <a href="/facts/Nucleotide/pQKEwlJI">nucleotides</a> as a <a href="/facts/Complementarity_(molecular_biology)/WQfqGlBJ">complementary</a> language. During transcription, a DNA sequence is read by an RNA <a href="/facts/Polymerase/hN2ECr7B">polymerase</a>, which produces a complementary, <a href="/facts/Antiparallel_(biochemistry)/IMsRKh5G">antiparallel</a> RNA strand called a <a href="/facts/Primary_transcript/4UXtKPHw">primary transcript</a>. </p><p>In <a href="/facts/Virology/doDESmsB">virology</a>, the term transcription is used when referring to mRNA synthesis from a viral RNA molecule. The <a href="/facts/Genome/tjhWET4V">genome</a> of many <a href="/facts/Orthornavirae/qG4evU2T">RNA viruses</a> is composed of <a href="/facts/Sense_(molecular_biology)/hcKgNvy6">negative-sense</a> RNA which acts as a template for positive sense viral messenger RNA - a necessary step in the synthesis of viral proteins needed for <a href="/facts/Viral_replication/btE3fu1w">viral replication</a>. This process is catalyzed by a viral <a href="/facts/RNA-dependent_RNA_polymerase/UgPn4rjz">RNA dependent RNA polymerase</a>. </p>