1. Replication 4

2. The End Replication Problem: Telomeres shorten with each S phase Ori DNA replication is bidirectional Polymerases move 5' to 3' Requires a labile primer 3' 5' 3' 5' 3' 5' Each round of DNA replication leaves 50-200 bp DNA unreplicated at the 3' end

3. Telomere Structure

4. Telomeres 'cap' chromosome ends

5. The structure of mammalian telomeres

6. Telomere Length (humans) Number of Doublings 20 10 Cellular (Replicative) Senescence Normal Somatic Cells (Telomerase Negative) Telomere also provide a means for "counting" cell division: telomeres shorten with each cycle Telomeres shorten from 10-15 kb (germ line) to 3-5 kb after 50-60 doublings (average lengths of TRFs) Replicative senescence is triggered when cells acquire one or a few critically short telomeres.

7. Telomerase prevents telomere shortening 3' 5' DNA Replication Telomerase DNA Polymerase Telomere shortening: telomeric chromosome fusions chromosome instability replicative senescence cell death Telomere length maintenance: essential for replicative immortality

8. Synthesis of telomeric sequences 1) Recognition 2) Elongation 3) Translocation DNA substrate binding to hTERT and RNA template Addition of nucleotides DNA substrate and enzyme repositioning CAAUCCCAAUC 3’ 5’ hTERT hTR 5’- GGTTAGGGTTAGGGTTAG 3’- CCAAT GGTTAGGGTTAGGGTTAG 4) Repeated translocation and elongation=repeat addition processivity

9. Telomere length (humans) Number of Doubling 20 10 Cellular (Replicative) Senescence Normal Somatic Cells (Telomerase Negative) Germ Cells (Telomerase Positive) + Telomerase Telomere Length and Cell Division Potential

10. Telomere related disease werner syndrome