BIOL 200 Chapter Notes -Smn2, Nuclear Membrane, Aromatic Amino Acids
23 Oct 2013
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Primary transcript: the initial mrna right after transcription, aka pre-mrna. Co-transcriptional: pre-mrna processing events (capping, splicing and polyadenylation) occur at the same time as the nascent mrna is being transcribed. Ribonucleoprotein (rnp) complexes: mrnas are never free rna molecules in the cell, but are associated with protein in rnp complexes. First: nascent pre-mrnps that are capped and spliced as they are transcribed. Third: cytoplasmic mrnps after export to the cytoplasm. Why: protect the pre-mrna from enzymes that digest uncapped mrnas (5"-exoribonucleases, distinguish pre-mrna from other types of rna in the nucleus. A cap is added to the 5" end after rna pol ii makes 25 nucleotides. The cap is 7-methylguanosine and methylated riboses. Enzyme associates with the phosphorylated ctd of rna pol ii. Only rna pol ii has a ctd tail. Capping enzyme removes y-phosphate from the 5" end of nascent mrna.
