12.Posttranscriptional modifications (maturation) of RNA in pro- and eukaryotes.
Covers how gene expression is adjusted after transcription, starting with RNA interference by small RNAs and alternative splicing, then transcript stability and mRNA degradation. It then sets out the 5' capping and 3' poly-A tailing steps, the splicing machinery and its snRNAs, and finally site-specific deamination and guide-RNA-directed uridine insertion or deletion in trypanosome mitochondria, with a worked example of calcitonin/CGRP splicing.
Topic 12 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 2 sections, about 423 words (3 min of reading), with 24 flashcards.
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Posttranscriptional modifications (maturation) of RNA in pro- and eukaryotes.
RNA processing –
Posttranscriptional modifications (maturation) of RNA in pro- and eukaryotes.
Gene expression can be controlled after transcription with mechanisms such as: RNA interference, Alternative splicing, RNA editing, Transcript stability, and mRNA degradation.
RNA interference:
Involves small RNA molecules.
Dicer chops double-stranded RNA into small RNA pieces.
micro-RNAs bind complementary RNA to prevent translation.
small interfering RNAs (siRNAs) degrade specific mRNAs before translation.
Alternative splicing:
Recognizes different splice sites in different tissues.
Mature mRNAs in each tissue contain different exons → different polypeptides from same gene.
Example: alternative splicing of calcitonin/CGRP gene on chromosome 11 (CGRP = calcitonin gene–related peptide).
Transcript stability and mRNA degradation:
Prokaryotic mRNAs have short half-lives (1–5 minutes).
