1. Transcription Page 319-324 Example problems: Page 324, #2,3,9

2. 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

3. Video • Transcription Video

4. Types of RNA • mRNA: messenger RNA • tRNA: transfer RNA • rRNA: ribosomal RNA

5. Steps of Transcription • Initiation • Elongation • Termination

6. 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…

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

8. Transcription Initiation • Promoter: gene promoter transcription region termination sequence

9. Transcription Initiation upstream downstream +1 negative numbers positive numbers start transcription

10. Transcription Elongation • 5’  3’ • Template strand

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

12. Transcription Bubble

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

14. 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

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

16. Post-transcriptional modifications • Splicing; • exons– expressed • introns– interfering

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

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