DNA coiling around the DNA stands presentation.pptx

dna coiling in the stands and coding of dna on different codons

1. DNA Supercoiling

2. Supercoiling arises in any helical or coiled structure in which the two strands are constrained in some way. DNA Supercoiling

3. Supercoiling of circular DNA Supercoiled DNA represents tertiary structure of DNA

4. Supercoiling of linear DNA

5. DNA Supercoiling Supercoiled DNA represents the tertiary structure of DNA. Supercoiling can be in the right-handed direction or left-handed direction. Right-handed supercoiling = Positive supercoiling Left-handed supercoiling = Negative supercoiling Positively supercoiled DNA is overwound DNA. Negatively supercoiled DNA is underwound DNA.

6. Supercoiling of circular DNA

7. Relaxed plasmid +vely supercoiled plasmid -vely supercoiled plasmid DNA Supercoiling

8. Supercoiling of circular DNA Underwound Overwound

9. Linking number (Lk) Twist (tw): Number of times two strands pass each other in a duplex. tw = 10 Writhe (wr): Number of times the duplex pass each other in supercoiled DNA. wr = 0 wr = 3 wr = 2 Lk = tw + wr

10. Linking number (Lk)

11. Supercoiling of circular DNA

12. Electrophoresis of supercoiled DNA Supercoiled DNA moves faster than relaxed DNA during agarose gel electrophoresis.

13. Supercoiling naturally appears in many biological processes such as DNA replication and transcription. Supercoiling of linear DNA

14. RNA polymerase + supercoils - supercoils Twin domain hypothesis Supercoiling during transcription

15. DNA topoisomerases During the process of replication, transcription, other cellular transactions there is accumulation of supercoils in the cell. Accumulation of supercoils is energetically unfavorable for the cell. Accumulation of supercoils inhibits the movement of polymerases along DNA during transcription and replication thereby inhibiting the process. James Wang: Cell should have enzymes to remove supercoils to ensure that transcription and replication goes on without any impediment in the cell. Topoisomerases are the enzymes that remove supercoils from DNA and control the degree of supercoiling in the cell.

16. DNA topoisomerases DNA topoisomerases can be broadly classified into two categories. (1) Type I topoisomerases (2) Type II topoisomerases Type I topoisomerases (1) Act by transiently breaking one of the two strands, passing the unbroken strand through the break, and rejoining the broken ends (2) Change Lk in the increments of one. (3) Do not need ATP. Type II topoisomerases Act by breaking both the strands, passing the duplex through the break, and rejoin the broken end. (2) Change Lk in the increments of two. (3) Need ATP

17. Type I topoisomerase : Mechanism of action

18. Electrophoresis of supercoiled DNA

19. Type II topoisomerase : Mechanism of action

20. Topoisomerase Inhibitors in Anticancer Therapy

21. Anticancer Treatments Over 200 types of cancers

22. Cell Cycle Possible cell cycle targets Topoisomerase i nhibitors

23. Topoisomerase I Inhibitors First inhibitors found in the wood bark used in traditional Chinese medicine Camptothecin Clinical Studies begin in 1970s and 1980s

24. Approved by FDA for ovarian and lung cancer Topotecan (Hycamtin ) Irinotecan (CPT11) Approved by FDA for colorectal cancer Camptothecin Topoisomerase I Inhibitors

25. Topoisomerase II Inhibitors Lung , testicular, bladder, prostate, stomach, and uterine cancers, as well as Hodgkin and non-Hodgkin lymphoma, mycosis fungoides , Kaposi’s sarcoma, Wilm’s tumor, rhabdomyosarcoma, Ewing’s sarcoma, neuroblastoma, and brain tumors. Etoposide VePesid Doxorubicin Ellipticine

26. Side Effects Hair Loss Nausea, Vomiting Skin rash Sores in mouth Diarrhea