chapter 38: rna processing in eukaryotes

what is 18S?

RNA component of small ribosomal subunit (40S)

what is 28S and 5.8S?

RNA component of large ribosomal subunit (60S)

small nucleolar ribonucleoproteins (snoRNPs)

directs chemical modifications at specific nucleotides before pre-rRNA is cleaved

RNA polymerase III

synthesizes tRNA precursor

explain how tRNA precursor is processed into mature tRNA

1. 5’ leader cleaved by RNase P

2. 3’ trailer removed by RNase Z, and nucleotides CCA are added

3. intron removed by endonuclease, with the resulting product joined by ligase

how is pre-mRNA processed?

1. caps protect 5’ ends from degradation

2. polyA tail added to 3’ end

3. introns removed and exons linked to form final mRNA in a process called splicing (by splicesome)

introns

non-coding sequences

exons

coding sequences

ribozymes

catalytic RNAs

draw out self-splicing reaction

guanosine attaches to 5’ end of intron and OH attaches to 3’ end of upstream exon. this OH group attacks end of intron, which joins the two exons and releases the intron.