2. DNA Repair Nucleotide Excision Repair XP and CS BiS222 By Jooyoung Chang 장주영 Class #01 / Stu. #20091259

3. Assembling a Car An analogy

4. Steps in building a CAR Blueprint Kept at company headquarters Safe from damage Copy Copy machine Copy of the blueprint for outside use Factory Copy sent to factory Workers and robots make the car using instruction

5. Steps in building a PROTEIN Blueprint DNA kept in Nucleus Somewhat safe from damage Copy RNA polymerase “copy machine” Copy DNA into RNA for use outside Factory RNA sent to “factory” Ribosomes make and assemble proteins

6. Q: Most devastating effect?  Mistake in the Blueprint!  Toyota (Jan. 2010)  Massive recall foot pedal  Mistake in blueprint-level  DNA Damage  Has devastating effects  DNA is the starting point of protein production, thus cell function

7. DNA Damage Example  Tumor suppressor genes  Gene that encodes protein: p53  Recognizes damaged DNA  And prevents mutant cell from replicating  If p53 is damaged  Mutated cells grow uncontrollably  And become tumorous!

8. Another Example  RNA polymerase genes  Copy machine  DNA to RNA step is JAMMED!  Cell cannot function  EX) Cockayne’s Syndrome, will be discussed in the flash video. JAMMED!

9. DNA is Fragile  Ionizing radiation often breaks DNA strands  Reactive chemicals, many of which are from the cell itself, cause structural alteration  UV radiation causes chemical alterations  Even thermal energy from the cell can cause spontaneous alterations, or lesions

10. DNA Repair to the Rescue!  The cell has a remarkable ability to repair DNA  These DNA repair mechanisms are responsible for repairing thousands of DNA alterations per day!

11. Repair Mechanisms  Base Excision Repair  Multi-step process that corrects non-bulky damage  Mismatch Repair  Corrects DNA replication errors  Double stranded breakage repair  Repairs complete cuts in the DNA strand  Nucleotide excision repair (NER)  Removes bulky lesions in the cell

12. Nucleotide Excision Repair  NER is perhaps the most flexible of the DNA repair pathways considering the diversity of DNA lesions it acts upon.  Pyrimidine dimers  Nucleotides with altered chemistry  Thymine dimers

13. Thymine Dimer H H H3CH3C O O N NN H H CH 3 O O N Ultraviolet Radiation Covalent Bonds DNA Backbone Thymine

14. RNA RNA Polymerase CS A CS B XPC Nucleotide Excision Repair TT= 5’ 3’ 1. Transcription-Coupled Pathway 2. Global Genomic Pathway

15. XPB XPD Nucleotide Excision Repair TT=5’ 5’ 3’ 3’ Hydrogen bonds TFII H

16. XPB XPD XP G ERCC 1 XPF Nucleotide Excision Repair TT=5’ 5’ 3’ 3’

17. XPB XP G ERCC 1 XPF TT= XPD Nucleotide Excision Repair 5’ 5’ 3’ 3’

18. DNA Polymerase δ / ε Nucleotide Excision Repair 5’ 5’ 3’ 3’ Ligase

19. Is NER really important?  If we want to see whether car tires are important,  Let someone ride a car without it.

20. Is NER really important?  If we want to see whether NER is important,  Let see what goes wrong in a cell and the organism when NER is dysfunctional!  Two diseases  Xeroderma Pigmentosum [XP]  Cockayne’s Syndrome [CS] (Remember the copy machine?)

21. What goes wrong in XP? Patients with Xeroderma Pigmentosum have mutated XP genes and cannot make proper XP enzymes. NER doesn’t function at normal levels, DNA damage is not repaired well, many genes cannot be used. XPB XPD XP G ERCC 1 XPF XP C

22. Symptoms of XP Skin- sunburns and freckles Cancer/Carcinoma- damaged tumor suppressor genes (1000 fold risk) Eye abnormalities Neurological Disorders in severe cases

23. Treatments? Avoid sunlight and wear protective coverings Dimericine® -T4N5 Liposome Lotion (FDA Fast Track Designation) Gene therapy using recombinant retroviruses – still under development XP affected Cell Proper XP genes VIRUS NER restored! T4 N5

24. What goes wrong in CS? Cockayne’s Syndrome is caused by mutation CSA and CSB genes Only the transcription coupled pathway is impaired – so active genes cannot be transcribed. Global pathway is unchanged – normal risks of cancer

25. Symptoms of CS Mutated CSA and CSB likely hinder transcription mechanisms affecting damaged and undamaged DNA alike Dwarfism, photosensitivity disorders, premature aging, and hearing loss No cure, treatment focuses on relief

26. Key points to take away DNA is under constant threat of damage Cells repair DNA as its used (transcribed) Cells repair DNA in the inactive state Malfunction in repair mechanisms lead to life-threatening diseases

27. REFERENCE Karp, Gerald. “Cell Biology” Pg 291 Pescarmona, Gianpiero. “DNA Breaks and Repair” Microsoft Clip Art