Page Example problems: Page 324, #2,3,9

Transcription The process of making… RNA review Very similar to DNA except: Has a ribose sugar instead of a deoxyribose Uses the base uracil instead of thymine Is generally single-stranded

Video Transcription Video

Types of RNA mRNA: messenger RNA tRNA: transfer RNA rRNA: ribosomal RNA

Steps of Transcription 1. Initiation 2. Elongation 3. Termination

RNA Polymerase The enzyme responsible for making RNA In prokaryotes: Only 1 RNA polymerase In eukaryotes: RNA Polymerase II: responsible for… RNA Polymerase I and III: responsible for…

Transcription Initiation What happens? Promoter: Generally high in A’s and T’s…WHY? TATA box TATAAT

Transcription Initiation Promoter: promotertranscription region termination sequence gene

Transcription Initiation +1 positive numbersnegative numbers upstream downstream start transcription

Transcription Elongation 5’  3’ Template strand

2. Transcription Elongation Antisense strand: Sense strand: 5’ A T T A C G A T C T G C A C A A G A T C C T 3’ 5’ A U U A C G A U C U G C A C A A G A U C C U 3’ 3’ T A A T G C T A G A C G T G T T C T A G G A 5’ SENSE STRAND ANTISENSE STRAND DNA mRNA

Transcription Bubble

3. Transcription Termination Termination sequence Termination sequences differ between prokaryotes and eukaryotes

Post-transcriptional modifications Primary transcript Modifications are done to stabilize and protect the RNA Poly(A) tail: Enzyme? 5’ cap: Enzyme? Unusual 5’-to-5’ triphosphate linkage

4. Posttranscriptional Modification 5’ 3’ 5’ cap added by capping enzyme complex primary transcript 3’ poly-A tail added by poly-A polymerase AAAAAAA mG

Post-transcriptional modifications Splicing; exons – expressed introns – interfering

4. Posttranscriptional Modification AAAAAAA mG exon intron introns removed by spliceosome proteins AAAAAAA mG exon mRNA transcript

4. Posttranscriptional Modification Spliceosomes are a series of small nuclear ribonucleoproteins (snRNP) snRNPs: cuts out intron sequences splices exon sequences together