1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Click to add text Chapter 16 The Molecular Basis of Inheritance

2. Fig. 16-7 (c) Space-filling model Hydrogen bond 3 end 5 end 3.4 nm 0.34 nm 3 end 5 end (b) Partial chemical structure(a) Key features of DNA structure 1 nm

3. Fig. 16-7a Hydrogen bond 3 end 5 end 3.4 nm 0.34 nm 3 end 5 end (b) Partial chemical structure(a) Key features of DNA structure 1 nm

4. Fig. 16-7a Hydrogen bond 3 end 5 end 3.4 nm 0.34 nm 3 end 5 end (b) Partial chemical structure(a) Key features of DNA structure 1 nm

5. Fig. 16-7b (c) Space-filling model

6. Fig. 16-8 Cytosine (C) Adenine (A)Thymine (T) Guanine (G)

7. Concept 16.2: Many proteins work together in DNA replication and repair The relationship between structure and function is manifest in the double helix The specific base pairing suggested a possible copying mechanism for genetic material Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

8. The Basic Principle: Base Pairing to a Template Strand Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: DNA Replication Overview

9. Fig. 16-9-1 A T G C TA TA G C (a) Parent molecule

10. Fig. 16-9-2 A T G C TA TA G C A T G C T A T A G C (a) Parent molecule (b) Separation of strands

11. Fig. 16-9-3 A T G C TA TA G C (a) Parent molecule AT GC T A T A GC (c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand (b) Separation of strands A T G C TA TA G C A T G C T A T A G C

12. DNA Replication: A Closer Look The copying of DNA is remarkable in its speed and accuracy More than a dozen enzymes and other proteins participate in DNA replication Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

13. Getting Started Replication begins at special sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble” A eukaryotic chromosome may have hundreds or even thousands of origins of replication Replication proceeds in both directions from each origin, until the entire molecule is copied Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: Origins of Replication

14. Fig. 16-12 Origin of replication Parental (template) strand Daughter (new) strand Replication fork Replication bubble Two daughter DNA molecules (a) Origins of replication in E. coli Origin of replicationDouble-stranded DNA molecule Parental (template) strand Daughter (new) strand Bubble Replication fork Two daughter DNA molecules (b) Origins of replication in eukaryotes 0.5 µm 0.25 µm Double- stranded DNA molecule

15. Fig. 16-12a Origin of replication Parental (template) strand Daughter (new) strand Replication fork Replication bubble Double- stranded DNA molecule Two daughter DNA molecules (a) Origins of replication in E. coli 0.5 µm

16. Fig. 16-12b 0.25 µm Origin of replicationDouble-stranded DNA molecule Parental (template) strand Daughter (new) strand Bubble Replication fork Two daughter DNA molecules (b) Origins of replication in eukaryotes

17. At the end of each replication bubble is a replication fork, a Y-shaped region where new DNA strands are elongating Helicases are enzymes that untwist the double helix at the replication forks Single-strand binding protein binds to and stabilizes single-stranded DNA until it can be used as a template Topoisomerase corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

18. Fig. 16-13 Topoisomerase Helicase Primase Single-strand binding proteins RNA primer 5 5 53 3 3

19. DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to the 3 end The initial nucleotide strand is a short RNA primer Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

20. An enzyme called primase can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template The primer is short (5–10 nucleotides long), and the 3 end serves as the starting point for the new DNA strand Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

21. Synthesizing a New DNA Strand Enzymes called DNA polymerases catalyze the elongation of new DNA at a replication fork Most DNA polymerases require a primer and a DNA template strand The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

22. Each nucleotide that is added to a growing DNA strand is a nucleoside triphosphate dATP supplies adenine to DNA and is similar to the ATP of energy metabolism The difference is in their sugars: dATP has deoxyribose while ATP has ribose As each monomer of dATP joins the DNA strand, it loses two phosphate groups as a molecule of pyrophosphate Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

23. Antiparallel Elongation The antiparallel structure of the double helix (two strands oriented in opposite directions) affects replication DNA polymerases add nucleotides only to the free 3  end of a growing strand; therefore, a new DNA strand can elongate only in the 5  to  3  direction Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

24. Along one template strand of DNA, the DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: Leading Strand

25. Fig. 16-15 Leading strand Overview Origin of replication Lagging strand Leading strandLagging strand Primer Overall directions of replication Origin of replication RNA primer “Sliding clamp” DNA poll III Parental DNA 5 3 3 3 3 5 5 5 5 5

26. To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: Lagging Strand

27. Fig. 16-16a Overview Origin of replication Leading strand Lagging strand Overall directions of replication 1 2

28. Fig. 16-16b1 Template strand 5 5 3 3

29. Fig. 16-16b2 Template strand 5 5 3 3 RNA primer 3 5 5 3 1

30. Fig. 16-16b3 Template strand 5 5 3 3 RNA primer 3 5 5 3 1 1 3 3 5 5 Okazaki fragment

31. Fig. 16-16b4 Template strand 5 5 3 3 RNA primer 3 5 5 3 1 1 3 3 5 5 Okazaki fragment 1 2 3 3 5 5

32. Fig. 16-16b5 Template strand 5 5 3 3 RNA primer 3 5 5 3 1 1 3 3 5 5 Okazaki fragment 1 2 3 3 5 5 1 2 3 3 5 5

33. Fig. 16-16b6 Template strand 5 5 3 3 RNA primer 3 5 5 3 1 1 3 3 5 5 Okazaki fragment 1 2 3 3 5 5 1 2 3 3 5 5 1 2 5 5 3 3 Overall direction of replication

34. Table 16-1

35. The DNA Replication Complex The proteins that participate in DNA replication form a large complex, a “DNA replication machine” The DNA replication machine is probably stationary during the replication process Recent studies support a model in which DNA polymerase molecules “reel in” parental DNA and “extrude” newly made daughter DNA molecules Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: DNA Replication Review

36. Proofreading and Repairing DNA DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides In mismatch repair of DNA, repair enzymes correct errors in base pairing DNA can be damaged by chemicals, radioactive emissions, X-rays, UV light, and certain molecules (in cigarette smoke for example) In nucleotide excision repair, a nuclease cuts out and replaces damaged stretches of DNA Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

37. Fig. 16-18 Nuclease DNA polymerase DNA ligase

38. Replicating the Ends of DNA Molecules Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes The usual replication machinery provides no way to complete the 5 ends, so repeated rounds of replication produce shorter DNA molecules Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

39. Fig. 16-19 Ends of parental DNA strands Leading strand Lagging strand Last fragment Previous fragment Parental strand RNA primer Removal of primers and replacement with DNA where a 3 end is available Second round of replication New leading strand New lagging strand Further rounds of replication Shorter and shorter daughter molecules 5 3 3 3 3 3 5 5 5 5

40. Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequences called telomeres Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules It has been proposed that the shortening of telomeres is connected to aging Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

41. If chromosomes of germ cells became shorter in every cell cycle, essential genes would eventually be missing from the gametes they produce An enzyme called telomerase catalyzes the lengthening of telomeres in germ cells Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

42. The shortening of telomeres might protect cells from cancerous growth by limiting the number of cell divisions There is evidence of telomerase activity in cancer cells, which may allow cancer cells to persist Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

43. Concept 16.3 A chromosome consists of a DNA molecule packed together with proteins The bacterial chromosome is a double- stranded, circular DNA molecule associated with a small amount of protein Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the nucleoid Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

44. Chromatin is a complex of DNA and protein, and is found in the nucleus of eukaryotic cells Histones are proteins that are responsible for the first level of DNA packing in chromatin Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: DNA Packing

45. Fig. 16-21a DNA double helix (2 nm in diameter) Nucleosome (10 nm in diameter) Histones Histone tail H1 DNA, the double helixHistones Nucleosomes, or “beads on a string” (10-nm fiber)

46. Fig. 16-21b 30-nm fiber Chromatid (700 nm) LoopsScaffold 300-nm fiber Replicated chromosome (1,400 nm) 30-nm fiber Looped domains (300-nm fiber) Metaphase chromosome

47. Chromatin is organized into fibers 10-nm fiber – DNA winds around histones to form nucleosome “beads” – Nucleosomes are strung together like beads on a string by linker DNA 30-nm fiber – Interactions between nucleosomes cause the thin fiber to coil or fold into this thicker fiber Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

48. 300-nm fiber – The 30-nm fiber forms looped domains that attach to proteins Metaphase chromosome – The looped domains coil further – The width of a chromatid is 700 nm Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

49. Most chromatin is loosely packed in the nucleus during interphase and condenses prior to mitosis Loosely packed chromatin is called euchromatin During interphase a few regions of chromatin (centromeres and telomeres) are highly condensed into heterochromatin Dense packing of the heterochromatin makes it difficult for the cell to express genetic information coded in these regions Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

50. Histones can undergo chemical modifications that result in changes in chromatin organization – For example, phosphorylation of a specific amino acid on a histone tail affects chromosomal behavior during meiosis Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

51. Fig. 16-UN2 Sugar-phosphate backbone Nitrogenous bases Hydrogen bond G C A T G G G A A A T T T C C C

52. Fig. 16-UN3 DNA pol III synthesizes leading strand continuously Parental DNA DNA pol III starts DNA synthesis at 3 end of primer, continues in 5  3 direction Lagging strand synthesized in short Okazaki fragments, later joined by DNA ligase Primase synthesizes a short RNA primer 5 3 5 5 5 3 3

53. Fig. 16-UN4

54. Fig. 16-UN5

55. You should now be able to: 1.Describe the contributions of the following people: Griffith; Avery, McCary, and MacLeod; Hershey and Chase; Chargaff; Watson and Crick; Franklin; Meselson and Stahl 2.Describe the structure of DNA 3.Describe the process of DNA replication; include the following terms: antiparallel structure, DNA polymerase, leading strand, lagging strand, Okazaki fragments, DNA ligase, primer, primase, helicase, topoisomerase, single-strand binding proteins Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

56. 4.Describe the function of telomeres 5.Compare a bacterial chromosome and a eukaryotic chromosome Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings