2. Looping the lagging strand to make both polymerases move in the same direction

3. The discovery of DNA polymerase. Arthur Kornberg and Bob Lehman pursued an enzyme in bacterial extracts that would elongate a chain of deoxyribonucleic acid just like glycogen synthase elongates a chain of glycogen. The enzymatic activity was unusual: 1) Needed a template which dictates what nucleotide was added: substrate was directing enzymatic activity 2) Needed a primer annealed to the template.

7. Wait a minute! John Cairns mutated the gene for DNA polymerase, polA, and the bacteria grew just fine! Either the polymerase hypothesis was all wrong,…… or there were other DNA polymerases in E. coli that carried out DNA synthesis in the polA strains.

10. Which polymerase is processive?

11. POLIII,  subunit PCNA

12. Clamp loaders hydrolyze ATP to load clamp How does one prove that the clamp ring is opened during loading?

15. Structure of a DNA polymerase (gp43 from phage RB69) Side view: Polymerase active site Top view with template-primer: Polymerase site And proofreading site

16. * Topoisomerases II change the linking number in steps of 2 by passing both strands of double-stranded DNA through a break. * Eukaryotic topoisomerases isolated to date only relax supercoiled DNA, while prokaryotic topoisomerases (gyrases) can, given ATP, add supercoils. * TopoII releases catenated daughter molecules at the end of replication. Inhibitors like etoposide are used in chemotherapy. Topoisomerases relax DNA by changing the DNA linking number

17. * Topoisomerases I change the linking number in steps of 1. They pass a single DNA strand through a nick.Topoisomerase I is a protein of the metaphase chromosome scaffold. * In interphase, topoisomerase is bound to the nuclear matrix. * The DNA replication machinery also appears bound to the matrix. * Inhibitor (camptothecin) also used in chemotherapy.

18. Topoisomerase action can be divided into three steps: nicking (1), strand passage (2); resealing (3).

19. 1 3 2 4 Cycle of topoisomerase activity inferred from structure How would you test that the subunits have to open at the lower end to release the T segment?