Chapter 11 - Transcription and Translation

8 s and 5s rrna the small ribosomal subunit contains

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Unformatted text preview: primary transcript (pre-RNA) can be spliced into three rRNAs: 28S, 18S, and 5.8S the 5S is synthesized from a separate precursor pre-rRNAis different than other RNAs it contains large numbers of methylated nucleotidfes and pseudouridine residues altered posttranscriptionally unaltered sections of the pre-rRNA are discarded during processing proposed scheme for processing mammalian rRNA: starts off as 45S RNA cleavage at sites 1 and 5 (5 and 3 external transcribed sequences) giving 41S rRNA cleavages at 2 or 3 depends on the type of the cell (cleavage at site 3 generates 32S intermediate) during final processing 28S and 5.8S are separated from each other processing of pre-rRNA is helped by small, nucleolar RNAs (snoRNAs) snoRNAs are packaged with proteins into snoRNPs (small nuclear ribonucleoproteins) snoRNAs modify bases in pre-RNAs nucleolus is the site of rRNA processing and also the location of the assembly ribosomal subunits Synthesis and Processing of tRNAs o o o o o o transfer RNAs tRNA genes are located in small clusters scattered around the genome a single cluster contains multiple copies of different tRNA genes a given tRNA can usually be found in more than one cluster tRNAs have promoter sequences within the coding region of the gene during processing, the tRNA precursor is trimmed and numerous bases must be modified at the end, it has anticodons (3 base pairs long ) which can interact with codons on mRNA 7...
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