1. The end replication problem: -DNA polymerase requires an OH group to attach bases too -There is no OH group at the extreme 5’ end of the lagging strand -Telomeres (the ends of chromosomes) contain repetitive sequences, no protein coding DNA

2. Telomerase uses RNA as a template to extend in the 3’ direction

4. RNA synthesis - Expression of the genome Properties: 1)Synthesis is de novo off of a template 2)Product (RNA) detaches from template (DNA) 3)Can tolerate more mistakes than DNA synthesis 4)Don’t replicate entire genome 5)Replicate portions repeatedly

5. DNA synthesis RNA transcription

6. RNA polymerases are made from many sub-units Homologous RNAP II performs most of the transcription in Eukaryotes *This lecture we will cover transcription in Prokaryotes

7. Overview of transcription steps Can diffuse away “locked” on Often starts and stops, repeats initial transcription “Breaks away” from promoter

8. Transcribed genes have “promoters” - sequence determines affinity for RNA polymerase

9. “Consensus” promoter - most common sequences

10. Alpha and Sigma subunits bind specific promoter sequences *Differences in alpha and sigma proteins can regulate transcription of specific genes

11. 4 functions of the Sigma subunit domains -Regions 3 and 4 bind the promoter -Region 2 melts DNA -Region 1 mimics DNA, moved when DNA melts

12. RNA polymerase ready to transcribe -Can synthesize “de novo” -Must hold 2 nucleotides in place long enough for binding to take place -Makes use of metal ions -Many transcribed sequences begin with an adenine

13. Several models for false starts to transcription

14. Relative positions of RNA polymerase Exonuclease activity

15. TRCF protein uses ATP to remove a stuck polymerase

16. Termination of transcription