Minsu Kim/minsu1

what is MicroRNA?

A microRNA (miRNA) 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. 

 

Synthesis and Function of miRNA

Structure of pre-miRNAs

overview of the structure of pri-miRNA showing cleavage

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 Dicer, and the others is Drosha

miRNAs function via base-pairing with complementary sequences within mRNA. As a result, these mRNA molecules are silenced, by one or more of the following processes:

 

• Cleavage of the mRNA strand into two pieces,
• Destabilization of the mRNA through shortening of its poly(A) tail, and
• Less efficient translation of the mRNA into proteins by ribosomes

 

miRNAs resemble the small interfering RNAs (siRNAs) of the RNA interference (RNAi) pathway, except miRNAs derive from regions of RNA transcripts that fold back on themselves to form short hairpins, whereas siRNAs derive from longer regions of double-stranded RNA. The human genome may encode over 1000 miRNAs, which are abundant in many mammalian cell types and appear to target about 60% of the genes of humans and other mammals