BCHM 4116 1st Edition Lecture 27 Outline of Last Lecture I Transcription initiation by RNA pol II requires TBP and GTFs Outline of Current Lecture 1 Eukaryotic Transcripts Processed and Delivered to Ribosome for Translation Current Lecture 29 5 Eukaryotic Transcripts Processed and Delivered to Ribosome for Translation a Transcription occurs on DNA in nucleus and translation occurs on ribosomes in cytoplasm b On way to cytoplasm transcripts undergo processing to form mature RNA i Eukaryotic genes are split genes 1 Exons coding regions 2 Introns non coding regions ii Post transcriptional processing of mRNA precursors involves capping methylation polyadenylylation and splicing 1 Capping methylation a 5 end of growing transcript is capped by addition of guanylyl residue i catalyzed by guanylyl transferase using GTP b Cap structure is methylated at the 7 position of the G residue i Additional methylations may occur at 2 O position o f2 nucleosides following 7 methyl G cap at 6amino group of 1st base adenine c 3 polyadenylylation i Termination does not normally occur until RNA pol II transcribed past a consensus AAUAAA seq known as polyadenylylation signal 1 Consensus AAUAAA is not poly A tail instead it defines position where poly A addition occurs ii A residues are not encoded in DNA but added posttranscriptionally by poly A polymerase These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute d Splicing i Splicing proceeds via formation of lariate ii Splicing depends on snRNPs 1 snRNPs U1 U2 U4 U5 U6 2 snRNPs form spliceosome a splicesome large complex i Assembly requires ATP ii Assembly iii 1 U1 binds to snRNP 5 splice site of pre mRNA iv U2 binds to snRNP v Triple snRNP complex U4 U6 U5 replaces U1 at 5 splice site iii Constitutive splicing every intron is removed every exon is incorporated iv Alternative splicing 1 Offers another level at which regulation of gene expression can operate
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