Concept 47 - Concept 17.3 Eukaryotic cells modify RNA after...

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Concept 17.3 Eukaryotic cells modify RNA after transcription. Enzymes in the eukaryotic nucleus modify the pre-mRNA before the genetic messages are dispatched to the cytoplasm. o During RNA processing, both ends of the primary transcript are usually altered. o In most cases, certain interior parts of the molecule are cut out and the remaining parts are spliced together. o These modifications help form an mRNA molecule that is ready for translation. At the 5 end of the pre-mRNA molecule, a modified form of guanine is added, the 5 cap . At the 3 end, an enzyme adds 50 to 250 adenine nucleotides, the poly-A tail . These modifications have three important functions. 1. They seem to facilitate the export of mRNA from the nucleus. 2. They help protect mRNA from hydrolytic enzymes. 3. They help the ribosomes attach to the 5 end of the mRNA. The parts of the mRNA that will not be translated into protein are referred to as UTRs (untranslated regions).
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Concept 47 - Concept 17.3 Eukaryotic cells modify RNA after...

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