1. 1 DNA and Replication

2. 2 History of DNA

3. 3 Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA Proteins were composed of 20 different amino acids in long polypeptide chains

4. 4 Transformation Fred Griffith worked with virulent S and nonvirulent R strain pneumonia bacteria He found that R strain could become virulent when it took in DNA from heat-killed S strain Study suggested that DNA was probably the genetic material

5. 5 Griffith Experiment

6. 6 History of DNA Viruses are made of DNA in a protein “coat” Experiments on viruses by Hershey & Chase proved that DNA was the cell’s genetic material Radioactive DNA was injected into bacteria!

9. 9 DNA Structure Rosalind Franklin took diffraction x-ray photographs of DNA crystals In the 1950’s, Watson & Crick built the first model (double helix) of DNA using Franklin’s x-rays

10. 10 Rosalind Franklin

11. Watson and Crick We’re big fat thieves!

12. Video: History of DNA Discovery Questions to Ponder… 1.Who was Linus Pauling and why was his DNA model incorrect? 2.How did Rosalind Franklin “help” Watson and Crick to develop their model of DNA?..\..\..\Downloaded Videos\The Secret of Life -- Discovery of DNA Structure.avi

13. 13 DNA Structure

14. The Basics DNA is a type of Nucleic Acid DNA: Deoxyribonucleic Acid Made of monomers called nucleotides Function: to store genetic information

15. 15 DNA Two strands coiled called a double helix Sides made of a sugar Deoxyribose bonded to phosphate (PO 4 ) groups Center made of nitrogen bases bonded together by weak hydrogen bonds

16. 16 DNA Double Helix Nitrogenous Base (A,T,G or C) “Rungs of ladder” “Legs of ladder” Phosphate & Sugar Backbone

18. 18 DNA Double helix is formed by nucleotides linked to one another Nucleotide made of:Nucleotide made of: Phosphate group 1.Phosphate group 5-carbon sugar 2.5-carbon sugar Nitrogenous base 3.Nitrogenous base

19. 19 DNA Nucleotide O=P-O OPhosphate Group Group N Nitrogenous base (A, G, C, or T) (A, G, C, or T) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose) O

20. 20 DNA Strands The part of a strand that ends with a phosphate group is called the 5 prime (5’) end The part of a strand that ends with a sugar is called the 3 prime (3’) end

21. Antiparallel Strands One strand of DNA goes from 5’ to 3’ The other strand is opposite in direction going 3’ to 5’ Strand 1: 5’ to 3’ Strand 2: 3’ to 5’

22. 22 Nitrogenous Bases Double ring PURINESDouble ring PURINES Adenine (A) Guanine (G) Single ring PYRIMIDINESSingle ring PYRIMIDINES Thymine (T) Cytosine (C) T or C A or G

23. 23 Base-Pairings Purines only pair with Pyrimidines Hydrogen bonds connect the bases CG 3 H-bonds

24. The process of specific bases bonding together to form the rungs of the ladder is called Complementary Base Pairing

25. 25 Chargaff’s Rule Adenine ThymineAdenine must pair with Thymine Guanine CytosineGuanine must pair with Cytosine G C TA

26. 26 Discovery of DNA Structure Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G) In a body or somatic cell: A = 30.3% T = 30.3% G = 19.5% C = 19.9%

27. 27 Question: Adenine CytosineIf there is 30% Adenine, how much Cytosine is present?

28. 28 Answer: CytosineThere would be 20% Cytosine Adenine (30%) = Thymine (30%)Adenine (30%) = Thymine (30%) Guanine (20%) = Cytosine (20%)Guanine (20%) = Cytosine (20%) Therefore, 60% A-T and 40% C-GTherefore, 60% A-T and 40% C-G

29. Question Write out the sequence of a strand complementary to the following strand… TTAGCATGG

30. Answer Original Strand:TTAGCATGG ComplementaryAATCGTACC Strand:

31. 31 DNA Replication

32. 32 Replication Facts DNA has to be copied before a cell dividesDNA has to be copied before a cell divides DNA is copied during the S or synthesis phase of interphaseDNA is copied during the S or synthesis phase of interphase New cells will need identical DNA strandsNew cells will need identical DNA strands

33. 33 Synthesis Phase (S phase) S phase during interphase of the cell cycle Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase DNA replication takes place in the S phase.

34. 34 DNA Replication Begins at Origins of ReplicationBegins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region)Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forksNew strands grow at the forks ReplicationFork Parental DNA Molecule 3’ 5’ 3’ 5’

35. 35 DNA Replication As the 2 DNA strands open at the origin, Replication Bubbles formAs the 2 DNA strands open at the origin, Replication Bubbles form Prokaryotes (bacteria) have a single bubble Eukaryotic chromosomes have MANY bubbles Bubbles

36. 36 Steps of DNA Replication 1) Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds copyright cmassengale

37. Steps of DNA Replication 2) Primase gathers nucleotides and brings them into the replication fork. A “primer” is created to start the new strand. 37

38. Steps of DNA Replication 3) The enzyme DNA Polymerase matches free nucleotides with the correct base pairs on the template (parent) strands. 38

39. copyright cmassengale39

40. copyright cmassengale40

41. Steps of DNA Replication 4) The enzyme ligase connects any “breaks” in the new strands and the 2 new strands rewind back together. The Big Question: Why are there “breaks” in the new strands at all?! 41

42. 42 DNA polymerase can only add nucleotides to the 3’ end of the DNADNA polymerase can only add nucleotides to the 3’ end of the DNA This causes the NEW strand to be built in a 5’ to 3’ directionThis causes the NEW strand to be built in a 5’ to 3’ direction RNAPrimer DNA Polymerase Nucleotide 5’ 3’ Direction of Replication

43. 43 Remember the Strands are Antiparallel

44. 44 Making New DNA Strands The Leading StrandThe Leading Strand is built into the replication fork copyright cmassengale

45. 45 The Lagging Strand isThe Lagging Strand is built in short sections in the opposite direction (out of the fork) This causes the “breaks” in the strand. copyright cmassengale

46. 46 Joining of Fragments of DNA The enzyme Ligase joins the sections together to make one strandThe enzyme Ligase joins the sections together to make one strand Lagging Strand DNA ligase DNA ligase 5’ 3’

47. A Quick Video to Help You Remember..\..\..\Downloaded Videos\DNA Replication Process.avi..\..\..\Downloaded Videos\DNA Replication Process.avi

48. 48 Proofreading New DNA DNA polymerase makes about 1 in 10,000 base pairing errorsDNA polymerase makes about 1 in 10,000 base pairing errors Enzymes proofread and correct these mistakesEnzymes proofread and correct these mistakes The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errorsThe new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

49. 49 DNA Damage & Repair Chemicals & ultraviolet (UV) radiation damage the DNA in our body cells Types of Repair: 1) Excision repair – when a repair enzyme removes damaged DNA 2) DNA polymerase and ligase work together to replace and bond the new nucleotides together