taking a Look at MicroRNAs

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MicroRNAs (miRNAs) are evolutionary conserved small (21-23 nucleotide long) non-coding RNA molecules that are involved in post-transcriptional regulation of gene expression. The human genome encodes for upward of 500 miRNAs and each can usually regulate a whole set of genes involved in various kinds of molecular mechanisms although a lot of mRNA targets of individual miRNAs are still not known. miRNAs are involved in regulation of crucial functions related to cell growth, development and differentiation and have already been linked with various diseases like cancer, heart disease etc. miRNAs can be encoded by their own genes or can sometimes be found in the introns of the genes they regulate thus undergoing the same transcriptional regulation. After transcription they are folded, processed and exported from the nucleus as a precursor dsRNA. In the cytoplasm they bind the Dicer endonuclease that cuts the RNA into short segments of approximately 21 nucleotides, which then bind the Argonaut protein where one strand is selected and remains bound to the protein and the other one is degraded. The guide strand together with the Argonaut and other proteins form the RNA Induced Silencing Complex (RISC). Through base complementarity between the guide strand and the mRNA, the complex can either inhibit translation or catalyze cleavage of the mRNA after which it is degraded. Unlike siRNAs that have perfect complementarity with the mRNA, the miRNAs have a partial complementarity with a

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