Chap 16 Molecular Basis Of Inheritance

1. Chap 16 Molecular Basis Of Inheritance DNA

4. Phage (virus) reproduction

5. Hershey and Chase Experiment • http://highered.mcgraw-hill.com/olc/dl/120076/bio21.swf

6. Fig. 18.4

7. Animation Link to Bacteriaphage page

9. Hershey and Chase • Conclusions • Since 32Pwas found on the inside of the bacteria, DNA was inserted into the bacteria • Since 32Pwas found in the baby viruses, DNA is the genetic materialtaking over the bacteria to make new viruses and being passed on to the new baby viruses • 30161-6

10. Structure of DNA • DNA is made of chains of nucleotides • a Nucleotide is made of three subunits • phosphorus group • 5 carbon sugar group • nitrogenous base B P S

13. Chargaff’s Rule • Chargaff found that the amount of adenine in an organism is always equal to the amount of thymine (A=T) • Also, he found that the amount of cytosine always equals the amount of guanine (C=G). • This suggested that DNA had some sort of regular structure where the pairing of these bases are involved

14. (b) (a) Rosalind Franklin Franklin’s X-ray diffraction Photograph of DNA Figure 16.6 Rosalind Franklin and her X-ray diffraction photo of DNA

16. WATSON AND CRICK • DNA is made of two strands of nucleotides chains that wind around each other • This DNA structure is called a: • double helix

17. DNA and RNA animation

18. 5 end G C O OH A T Hydrogen bond P 3 end –O O T A OH O H2C A T 1 nm O O CH2 O C G P O O– –O 3.4 nm O P C G O O H2C O G C T A O CH2 O O G C P O O– –O O P O O H2C O G C T A O CH2 O O P T A O –O O– O P O A T O H2C O A T T A O CH2 OH O O– 3 end P O G C O 0.34 nm 5 end T A (a) Key features of DNA structure (b) Partial chemical structure (c) Space-filling model Figure 16.7 The double helix

19. A Purine always pairs with a Pyrimidine A with T G with C. X-Ray diffraction of DNA indicated that DNA was 2nm thick

20. Purine + Purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width Consistent with X-ray data Unnumbered Figure p. 298

21. N O H CH3 N N N N H Sugar N N O Sugar Adenine (A) Thymine (T) H O N H N N N H N Sugar N N N O H Sugar H Cytosine (C) Guanine (G) Figure 16.8 Base pairing in DNA H

22. Antiparallel

23. DNA REPLICATION • DNA must make a copy of itself during Interphase • Watson and Crick postulated that the DNA molecule unzipped itself between the bases (because of the weak bonds) • Once opened, the exposed bases could serve as a template, allowing floating nucleotides to bond with them and follow their pattern in forming new DNA strands

25. Link to DNA Replication DEMO http://highered.mcgraw-hill.com/olc/dl/120076/micro04.swf Link to DNA Game

27. Old DNA strands act as a template for the new DNA strands New DNA is half old and half new

28. Semiconservative REPLICATION • Evidence for replication came from the work of Messelson and Stahl • They used a heavy isotope of Nitrogen to make ‘heavy’ strands of DNA • New DNA created with the heavy nitrogen was half heavy and half light • DNA replication is semiconservative • 30172

29. Messelson Stahl Animation • http://highered.mcgraw-hill.com/olc/dl/120076/bio22.swf • http://www.sumanasinc.com/webcontent/animations/content/meselson.html

30. EXPERIMENT Matthew Meselson and Franklin Stahl cultured E. coli bacteria for several generations on a medium containing nucleotide precursors labeled with a heavy isotope of nitrogen, 15N. The bacteria incorporated the heavy nitrogen into their DNA. The scientists then transferred the bacteria to a medium with only 14N, the lighter, more common isotope of nitrogen. Any new DNA that the bacteria synthesized would be lighter than the parental DNA made in the 15N medium. Meselson and Stahl could distinguish DNA of different densities by centrifuging DNA extracted from the bacteria. Bacteria cultured in medium containing 15N Bacteria transferred to medium containing 14N 2 1 3 4 RESULTS Less dense DNA sample centrifuged after 40 min (after second replication) DNA sample centrifuged after 20 min (after first replication) More dense The bands in these two centrifuge tubes represent the results of centrifuging two DNA samples from the flask in step 2, one sample taken after 20 minutes and one after 40 minutes. Figure 16.11 Does DNA replication follow the conservative, semiconservative, or dispersive model?

31. CONCLUSION Meselson and Stahl concluded that DNA replication follows the semiconservative model by comparing their result to the results predicted by each of the three models in Figure 16.10. The first replication in the 14N medium produced a band of hybrid (15N–14N) DNA. This result eliminated the conservative model. A second replication produced both light and hybrid DNA, a result that eliminated the dispersive model and supported the semiconservative model. First replication Second replication Conservative model Semiconservative model Dispersive model animation

32. New DNA is half HEAVY and half LIGHT Only two strands are half heavy

35. DNA Polymerase III adds a nucleotide only at the 3’ end.

37. DNA Polymerase only adds on to the 3’ end animation

39. Second animation

41. Table 16.1 Bacterial DNA replication proteins and their functions

42. Leading strand is left with a gap after each replication – because there is no 3’ end to attach DNA to - the gap gets wider and wider if there is no enzyme to repair the gap

43. Telomerase is a special enzyme with a built-in RNA section that allows for the lengthening of the 3’ side – the other 5’ side is lengthened in the normal backstitch pattern

44. 1 µm Figure 16.19 Telomeres

45. A thymine dimer distorts the DNA molecule. 3 2 4 1 A nuclease enzyme cuts the damaged DNA strand at two points and the damaged section is removed. Nuclease Repair synthesis by a DNA polymerase fills in the missing nucleotides. DNA polymerase DNA ligase DNA ligase seals the Free end of the new DNA To the old DNA, making the strand complete. Figure 16.17 Nucleotide excision repair of DNA damage

46. Do Lab Simulation at this site http://www.midpac.edu/~biology/Intro%20Biology/PH%20Biology%20Lab%20Simulations/dnarep/intro.html Do Self Quiz at the end – print out to turn in!

47. 0 Chapter 16 The Molecular Basisof Inheritance

48. Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. What percent of the nucleotides in this sample will be thymine? • 12 • 24 • 31 • 38 • It cannot be determined from theinformation provided.

49. In an analysis of the nucleotide composition of DNA, which of the following is true? • A = C • A = G and C = T • A + C = G + T • A + T = G + C • Both B and C are true

50. Imagine the following experiment is done: Bacteria are first grown for several generations in a medium containing the lighter isotope of nitrogen, 14N, then switched into a medium containing 15N. The rest of the experiment is identical to the Meselson and Stahl experiment. Which of the following represents the band positions you would expect after two generations?*