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From Biolecture.org
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<p>A <strong>microRNA</strong> (<strong>miRNA</strong>) is a small non-coding RNA molecule (containing about 22 nucleotides) found in plants, animals and some viruses, that functions in RNA silencing and post-transcriptional regulation of gene expression. miRNA are encoded in the genome as segments of longer transripts. their characteristic structure helps identify them and predict the target genes they might regulate. </p>
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<h1>Synthesis and Function of miRNA</h1>
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<td><img alt="" src="/ckfinder/userfiles/images/%EA%B7%B8%EB%A6%BC1(2).jpg" style="height:200px; width:300px" /></td>
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<td>Structure of pre-miRNAs</td>
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<td><img alt="" src="/ckfinder/userfiles/images/%EA%B7%B8%EB%A6%BC2(1).png" style="height:200px; width:300px" /></td>
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<td>overview of the structure of pri-miRNA showing cleavage</td>
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<p>miRNAs are derived from precursor RNAs that are encoded by genes. their characteristic structure helps identify them and predict the target genes they might regulate. the functional form of a miRNA IS typically ~21 or 22 nucleotides. These short RNAs are generated by two RNA cleavage reactions from a longer RNA transcript (called a pri-RNA, for "primary") that carries a hairpin-shaped scondary structure. The first cleavage liverates the stem- loop, called the pre-miRNA ; the second generates the mature miRNA from the pre-miRNA. The two cleavage reactions required to generate the miRNA grom these primary trnascipts are mediated by tow distinct RNases. One is <strong>Dicer</strong>, and the others is <strong>Drosha</strong></p>
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