DNA: (Deoxyribonucleic Acid) The Genetic material of all living organisms

1. DNA DNA: (Deoxyribonucleic Acid) The Genetic material of all living organisms

2. DNA • Inheritance has its molecular basis in the precise replication and transmission of DNA from parent to offspring.

3. DNA History Was first discovered by Frederick Meissner (german physician) in 1860s while he was changing puss covered wound dressings

4. 1928:Frederick Griffith • Performed experiments which provided evidence that genetic material is a particular chemical • Griffith was trying to find a vaccine against Streptococcus pneumoniae( bacteria that causes pneumonia)

5. Griffiths Experiment • Experiment: inject live S strain into mice • Results: mice die • Conclusion: strain is pathogenic

6. Griffiths Experiment • Experiment: inject mice with live R strain • Results: mice live • Conclusion: R strain not pathogenic

7. Griffiths Experiment • Experiment: Inject mice with heat-killed S strain • Results: mice live • Conclusion: heat kills bacteria and it is no longer pathogenic

8. Griffiths Experiment • Experiment: mix heat killed S strain with live R strain • Results: mice die • Conclusion: something chemical in nature moved from the S strain to the R strain making it pathogenic

10. History • By the 1940s, scientist know that chromosomes carried hereditary material that consisted of DNA and protein. • Most researchers thought that protein was the genetic material

11. Oswald Avery

12. Oswald Avery • 1944 Demonstrated that DNA alone from virulent bacterium can transform nonvirulent bacterium. • Provided more evidence that DNA is genetic material came from studies of bacteriophages ( virus that infects bacteria)

13. 1947 Developed Chargaffs rule of pairing nucleotides: Adenine---Thymine Cytocine----Guanine Erwin Chargaff

14. Watson and Crick

15. Watson and Crick • Watson and Crick built a scale model of a double helix that would conform to data and known chemistry of DNA • They proposed a ladder-like molecule that twisted into a spiral ( double helix), with sugar and phosphate backbones and nitrogen base pairs as rungs of the ladder

16. Watson and Crick • In April 1953, Watson and Crick’s new model of DNA structure was published in the British Journal of Nature. • This model for the DNA structure suggested a template mechanism for DNA replication…and was called a semiconservative model for DNA replication

17. semiconservative model for DNA replication • Watsons and Crick’s model suggested: • The 2 DNA strands separate • Each strand is a template for assembling a complementary strand • Nucleotides line up along the template according to base pairing rules • Enzymes link the nucleotide together • Each new DNA strand has one old and one new strand

18. Rosalind Franklin • Rosalind Franklin's x-ray diffraction work gave Watson and Crick the key to unlocking the structure of DNA. • She died before she could receive appropriate recognition of her contribution. She did not receive the Nobel Prize (not administered posthumously).

19. Rosalind Franklin

20. Martha Chase & Alfred Hershey (1952)

21. Martha Chase & Alfred Hershey (1953) Find that only DNA from virus enters cells and directs reproduction of new viruses

23. The Meselson - Stahl Experiment 1958"DNA Replication is Semiconservative • They proposed that when the time came for DNA to be replicated, the two strands of the molecule: • separated from each other but • remained intact as each served as the template for the synthesis of • a complementary strand. • When the replication process is complete, two DNA molecules — identical to each other and identical to the original — have been produced

24. History • DNA • Comprised of genes • In non-dividing cell nucleus as chromatin • Protein/DNA complex • Chromosomes form during cell division • Duplicate to yield a full set in daughter cell

25. History • DNA • The 5 carbon sugar (PENTOSE) is Deoxyribose • It is double stranded • DNA is found in the nucleus of the cell • Composed of sugar, phosphate and nitrogen base pairs

29. DNA is a Double Helix • Nucleotides • A, G, T, C • Sugar and phosphate form the backbone • Bases lie between the backbone • Held together by H-bonds between the bases • A-T – 2 H bonds • G-C – 3 H bonds

30. H - Bonds • Base-pairing rules • AT only (AU if DNA-RNA hybrid) • GC only • DNA strand has directionality – one end is different from the other end • 2 strands are anti-parallel, run in opposite directions • Complementarity results • Important to replication

31. Helical Structure

32. Nucleotides as Language • We must start to think of the nucleotides – A, G, C and T as part of a special language – the language of genes that we will see translated to the language of amino acids in proteins

33. Genes as Information Transfer • A gene is the sequence of nucleotides within a portion of DNA that codes for a peptide or a functional RNA • Sum of all genes = genome

34. DNA collected from cheek cells

36. DNA Replication General mechanism of DNA replication is conceptually simple, but the actual process is complex.

37. DNA Replication • Semiconservative • Daughter DNA is a double helix with 1 parent strand and 1 new strand • Found that 1 strand serves as the templatefor new strand

38. DNA Template • Each strand of the parent DNA is used as a template to make the new daughter strand • DNA replication makes 2 new complete double helices each with 1 old and 1 new strand

39. Steps of DNA Replication • Step 1: Origin of replication • Step 2: Strand separation • Step 3: Priming • Step 4: Synthesis of new DNA Strand • Step 5: Proof reading • Steps 3 and 4 happen simultaneously

40. Step 1. Origin of replication • DNA replication begins at a special site call the origin of replication • The ‘DNA double helix open at the origin and replication forks spread in both directions away from the central initiation point creating a replication bubble.

41. Replication Origin • Site where replication begins • 1 in E. coli • 1,000s in human • Strands are separated to allow replication machinery contact with the DNA • Many A-T base pairs because easier to break 2 H-bonds that 3 H-bonds • Note anti-parallel chains

42. Step 2: Strand separation • When DNA replicates, many different proteins work together to accomplish the following steps: • The two parent strands are unwound with the help of DNA helicases ( an enzyme).

43. Step 2: Strand Separation • Single stranded DNA binding proteins attach to the unwound strands, preventing them from winding back together. • Topoisomerase: Is another protein that serves to relieve the stress and untangle any kinks or snarls in the DNA

44. Step 3 & 4: Priming and Synthesis of New DNA Strand • The strands are held in position, binding easily to DNA polymerase, which catalyzes the elongation of the leading and lagging strands. (DNA polymerase also checks the accuracy of its own work!). • All is according to the base-pairing rule

45. Step 3 & 4: Priming and Synthesis of New DNA Strand • While the DNA polymerase on the leading strand can operate in a continuous fashion, RNA primer is needed repeatedly on the lagging strand to facilitate synthesis of Okazaki fragments.

46. Step 3 & 4: Priming and Synthesis of New DNA Strand • DNA primase, which is one of several polypeptides bound together in a group called primosomes, helps to build the primer. • A primer is a short segment of RNA made by an enzyme called primase

47. Step 3 & 4: Priming and Synthesis of New DNA Strand • Finally, each new Okazaki fragment is attached to the completed portion of the lagging strand in a reaction catalyzed by DNA ligase.

48. Step 5: Proof Reading and DNA Repair • There are more than 50 different types of DNA repair enzymes, but most perform 1 of 2 different types of repair. • 1. Directly reversing the change. • 2. Excision repair: The damage segment is excised by one repair enzyme and the remaining gap is filled in by base-pairing nucleotides

49. Legend: