1. 2007-2008 Synthesis of DNA June.21.2010

2. DNA synthesis occurs by the process of replication. During replication, each of the two parental strands of DNA serves as a template for the synthesis of a Complementary strand.

3. Each molecule generated by the replication process contains one intact parental strand and one newly synthesized strand .

4. In eukaryotes, DNA replication occurs during the S phase of the cell cycle The cell divides during the next phase ( M ), and each daughter cell receives an exact copy of the DNA of the parent cells.

5. Cultured MDCK cells Day 1 Day 3

6. Watson and Crick 1953 article in Nature

7. Double helix structure of DNA “ It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Watson & Crick

11. Bonding in DNA … . strong or weak bonds? How do the bonds fit the mechanism for copying DNA? 3  5  3  5  covalent phosphodiester bonds hydrogen bonds

20. energy 3  5  5  5  3  need “primer” bases to add on to energy energy energy 3  no energy to bond energy energy energy 3  5   ligase

22. Replication fork / Replication bubble leading strand lagging strand leading strand lagging strand leading strand lagging strand DNA polymerase III 5  3  5  3  5  3  3  5  5  3  5  3  5  3  5  3  growing replication fork growing replication fork 5  5  5  5  5  3  3  5  5  5  3 

27. Replication fork 3’ 5’ 3’ 5’ 5’ 3’ 3’ 5’ helicase SSB = single-stranded binding proteins primase DNA polymerase III DNA polymerase III DNA polymerase I ligase Okazaki fragments leading strand lagging strand SSB direction of replication

31. What does it really look like? 1 2 3 4

32. 2007-2008 Any Questions??

35. 5  3  3  5  3  5  3  5  no energy to bond 

36. energy 5  3  3  5  3  5  3  5  ligase

38. Replication fork 3’ 5’ 3’ 5’ 5’ 3’ 3’ 5’ direction of replication

40. Bidirectional replication of a circular chromosome Replication begins at the point of origin ( oriC ) and proceeds in both directions at the same time.

41. Unwinding of Parental Strands Topoisomerases: can break phosphodiester bonds and rejoin them relieve the supercoiling of the parental duplex caused by unwinding . DNA gyrase is a major topoisomerase in bacterial cells.

42. 以上です。