1. 1.Structures and Functions of Nucleic Acids 2.Organization and Content of Genomes 3.DNA Replication 4.The Mutability and Repair of DNA 5.DNA Recombination 6.Transcription and RNA Processing 7.Translation 8.Regulation of Gene Expression 9.Techniques of Molecular Genetics Introduction to Molecular Genetics http://priede.bf.lu.lv/http://priede.bf.lu.lv/ Studiju materiāli / MolekularasBiologijas / Ievads MolGen / EN

2. Molecular Biology of the Gene, 5th Edition DNA replication

3. The replication of DNA is a complex, multi-step process, involving many enzymes

4. Nucleotide sequence of a DNA strand (the template strand) is copied through complementary base pairing into complementary sequence DNA synthesis is TEMPLATED

5. DNA polymerase (enzyme that does the work) needs a single-stranded template, primer and dNTPs Molecular Biology of the Gene, 5th Edition

6. DNA is always synthesized in the 5’-to-3’ direction Molecular Biology of the Gene, 5th Edition

7. DNA polymerase resembles a hand that grips primer-template junction

8. DNA polymerase ‘monitors’ ability of the incoming nucleotide to base-pair with the template nucleotide Molecular Biology of the Gene, 5th Edition

9. Yet, a wrong base is occasionally added (when it is in an unusual tautomeric form) Molecular Biology of the Gene, 5th Edition

10. EXONUCLEOLYTIC PROOFREADING by DNA polymerase corrects most of these errors primer template Please, be so kind and find an error in this figure!

11. EXONUCLEOLYTIC PROOFREADING by DNA polymerase corrects most of these errors

12. DNA replication is SEMICONSERVATIVE Each strand of parental DNA serves as a template for a new complementary strand The 2 new double helixes each have 1 parental strand and 1 newly synthesized strand

13. Should it necessarily be so? Life The Science of Biology, 7th Edition

14. Meselson and Stahl (1958) proved that replication is semiconservative

15. Both strands are synthesized together at the REPLICATION FORK Lewin, Genes

16. There is a problem with the simplest model direction of replication direction of strand growth direction of strand growth

17. The replication fork is ASYMETRIC: one strand (leading) grows continuously, while the other (lagging) is synthesized as fragments

18. Two DNA polymerases operate at the replication fork Molecular Biology of the Gene, 5th Edition

19. Sliding clamp helps DNA polymerase not to fall off the template Molecular Biology of the Gene, 5th Edition

20. DNA polymerase needs a primer: primer (RNA!) is provided by DNA primase

21. Lagging strand is synthesized stepwise (RNAse H)

22. DNA ligase uses ATP to seal the nicks between fragments (ligation reaction)

23. Molecular Biology of the Gene, 5th Edition DNA polymerase needs a single-stranded DNA template: DNA helicase ‘opens’ the parental double helix

24. DNA polymerase needs a single-stranded DNA template: SSB proteins stabilize the unwound strands

25. The ‘winding’ problem Lehninger. Principles of Biochemistry, 3rd Edition

26. Topoisomerases remove positive supercoils Molecular Biology of the Gene, 6th Edition

27. The major types of proteins at a bacterial replication fork

28. The proteins involved in replication are arranged in a complex

29. Replication is initiated at the origins (ori) of replication

30. Mechanism of initiation in bacteria

31. Bacterial chromosomes are replicated from single origin

32. Eukaryotic chromosomes are replicated from many origins Molecular Biology of the Gene, 5th Edition

33. Eukaryotic chromosomes have redundancy of ori; all origins are inactivated by DNA replication

34. New nucleosomes are assembled right behind the replication fork

35. Patterns of histone modification can be faithfully inherited

36. Inheritance of chromatin structures is a mechanism of the EPIGENETIC INHERITANCE Any heritable difference in the phenotype of a cell that does not result from changes in the nucleotide sequence of DNA Specific epigenetic phenomena: 1. dosage compensation: a) X-chromosome inactivation; b) mono-allelic expression; 2. imprinting (parent-of-origin specific differences in gene activity)

37. The End Replication Problem Molecular Biology of the Gene, 6th Edition

38. Solving the end replication problem: TELOMERES & TELOMERASE Molecular Biology of the Gene, 5th Edition

39. Bacterial chromosomes have no ends & hence no end replication problem Molecular Biology of the Gene, 5th Edition

40. Single-stranded genomes (viruses) replicate through synthesis of complementary strands

41. Why is the genetic information stored in form of double-stranded DNA in all cells?