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The miRNAs act as post-transcriptional silencers, as they are similar to specific mRNAs and regulate their stability and translation. They are small endogenous non-coding ribonucleic acid (RNA) molecules, with about 22 nucleotides, which act as regulators of gene expression in plants and animals, at the post-transcriptional level through the cleavage of a target messenger RNA (mRNA) or repression of translation.
In general, most miRNA genes are transcribed by RNA polymerase II in the nucleus in primary miRNAs (pri-miRNAs). Individually, a pri-miRNA can produce a single miRNA or contain groups of two or more miRNAs that are processed from a common primary transcript. These long pri-miRNA are cleaved by a complex comprising the double-stranded RNAse III enzyme (DROSHA) and its essential cofactor, the binding protein DGCR8 (DiGeorge Syndrome Critical Region 8 protein) in mammals. DROSHA contains two domains of RNAse III, each of which cleaves a strand of the RNA resulting in the precursor microRNA (pre-miRNA) with about 70 base pairs, which contains a double-stranded stretch and a single-stranded loop, forming a structure in clamp. The pre-miRNA is exported to the cytoplasm by the protein exportin-5 (XPO-5), where it is cleaved by DICER1, an RNAse III that assesses the 3 'and 5' ends of the pre-miRNA, generating a mature miRNA with about 22 nucleotides. The processing of pre-miRNA by Dicer promotes the unfolding of the RNA duplex in the form of a clamp. The position in the formation of the clamp can also influence the choice of tape.
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A negative feedback initiated by the external simuli or the products of a reaction aims to reduce the products/ output of the reaction. Hence In negative feedback the stimulus is reduced. An example of a negative feedback would be if a person had an elevated body temperature, the homeostatic response would be to lower the body temperature.
<span>The causes for recent amphibian declines are many, beacuse of an emerging disease called chytridiomycosis . Chytridiomycosis is a disease caused by the fungal chytrid pathogen Batrachochytrium dendrobatidis.
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Evolution is the gradual change in the inherited traits of a population over several generations. natural selection is a mechanism where the members of a population best suited to their environment have the best chance of surviving to pass their genes
