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The tailing of hnRNA, which involves the addition of a poly-A tail to the 3' end of the mRNA molecule, occurs after transcription and before the mRNA is released from the nucleus. This process helps stabilize the mRNA and facilitate its export to the cytoplasm for translation.

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The tailing of hnRNA, which involves the addition of a poly-A tail to the 3' end of the mRNA molecule, occurs after transcription and before the mRNA is released from the nucleus. This process helps stabilize the mRNA and facilitate its export to the cytoplasm for translation.

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Exon skipping, also known as alternative splicing is a process whereby the exons are cut from a genetic sequence (pre-mRNA or hnRNA) and rearranged multiple ways into different mRNA molecules. This allows for a single gene to code for several proteins and isoproteins. Seen in Eukaryotes only.

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In the nucleus, RNA is transcribed from the entire gene. The genes contain both introns and exons. Only the exons contain the coding information for the protein. After transcription these long RNAs (called hnRNA) are processed to remove the introns. After adding a poly A tail, and a cap on the 5' end, the now much smaller RNA is exported into the cytosol where it can be translated.

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Most, but not allPrior to 1967, the assumption was that all biological catalysts were proteins. But an investigation into RNA splicing showed that there was no protein involved in cutting introns out of hnRNA (pre-RNA). In fact, the molecule responsible for breaking the phosphodiester bonds was snRNA (small nuclear RNA). snRNA and associated proteins are together called snRNPs (snurps), which gather in a spliceosome. The hnRNA is fed through the spliceosome and the snRNA breaks and reattaches bonds. From this point on, it was clear that ribonucleic acids could act as enzymes, and proteins were not alone. Enzymes that are ribonucleic acids are referred to as ribozymes.
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mRNA, or messenger RNA is single stranded, and so are transfer RNA, snRNA, hnRNA, and ribosomal RNA. The exception are some viral RNA's, that can be double stranded. Remember that despite having Uracil instead of Thymine, RNA can base pair anyway, just like in the case of the beforementioned RNA-viruses.

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