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CHAPTER 38 RNA Processing in Eukaryotes Problems: 1-5,7,9-11,14 Primary transcripts are processed. e.g. pre-mRNA is: • Capped • Poly adenylated • Spliced 38:1 Processing of Ribosomal RNA RNA Pol I snoRNPs 40S ribosomal 60S ribosomal subunit Subunit (also includes a 5S rRNA that is made by RNA Pol III) 38:2 Processing of Transfer RNA RNA Pol III • Removal of intron. • Cleavage of 5’-leader. • Removal of 3-trailer. • Addition of – CCA at 3’end. • Base modification. 38:3 Processing of Messenger RNA RNA Pol II Polyadenylation Capping Splicing Capping • Guanylate base is methylated at N-7, Step (3) 2-Hydroxyl groups of last two riboses may also be methylated, Step (4) Increase stability of mRNA. Enhance mRNA translation. Polyadenylation (CPSF = cleavage and polyadenylation specificity factor) Increase stability of mRNA; increase half-life. Enhance mRNA translation. Splicing of mRNA Polypyrimidine tract snRNP Splicing Mutations → Disease Alternative Splicing → Protein Diversity 2n = different mRNAs (proteins) n = number of alternative splice sites Transcription and Processing of mRNA are Coupled CTD (carboxy terminal domain) = YSPTSPS amino acid sequence at the – COOH terminal of RNA polymerase II. Phosphorylation of the indicated S residues leads the CTD to binding of the factors required for mRNA processing. The following are all coupled to mRNA transcription: 1. Capping 2. Splicing 3. Polyadenylation Post-transcriptional RNA Editing 38:4 Self-Splicing of Messenger RNA Ribozymes (group 1 type) are catalytic RNAs Lipid transport in the liver-lipids synthesized in the cell. Stop codon Group 2 uses the 2’-OH of an A-residue in the intron instead of a G) http://ibiomagazine.org/issues/augustissue/discvering-ribozymes.html Synthesized in intestine and transport of dietary lipids chylomicrons.