DNA Structure and Function. Chapter 13

Transcription

1 DNA Structure and Function Chapter 13

2 Impacts, Issues Here Kitty, Kitty, Kitty, Kitty, Kitty Clones made from adult cells have problems; the cell s DNA must be reprogrammed to function like the DNA of an egg

3 13.1 The Hunt for DNA Investigations that led to our understanding that DNA is the molecule of inheritance reveal how science advances

4 Early and Puzzling Clues 1800s: Miescher found DNA (deoxyribonucleic acid) in nuclei Early 1900s: Griffith transferred hereditary material from dead cells to live cells Mice injected with live R cells lived Mice injected with live S cells died Mike injected with killed S cells lived Mice injected with killed S cells and live R cells died; live S cells were found in their blood

5 Griffith s Experiments

6 R S R A Mice injected with live cells of harmless strain R do not die. Live R cells are in their blood. B Mice injected with live cells of killer strain S die. Live S cells are in their blood. C Mice injected with heat-killed S cells do not die. No live S cells are in their blood. D Mice injected with live R cells plus heat-killed S cells die. Live S cells are in their blood. Fig. 13-2, p. 204

7 R S R A Mice injected with live cells of harmless strain R do not die. Live R cells are in their blood. B Mice injected with live cells of killer strain S die. Live S cells are in their blood. C Mice injected with heat-killed S cells do not die. No live S cells are in their blood. D Mice injected with live R cells plus heat-killed S cells die. Live S cells are in their blood. Stepped Art Fig. 13-2, p. 204

8 Animation: Griffith s experiment

9 Avery and McCarty Find the Transforming Principle 1940: Avery and McCarty separated deadly S cells (from Griffith s experiments) into lipid, protein, and nucleic acid components When lipids, proteins, and RNA were destroyed, the remaining substance, DNA, still transformed R cells to S cells Conclusion: DNA is the transforming principle

10 Confirmation of DNA s Function 1950s: Hershey and Chase experimented with bacteriophages (viruses that infect bacteria) Protein parts of viruses, labeled with 35 S, stayed outside the bacteria DNA of viruses, labeled with 32 P, entered the bacteria Conclusion: DNA, not protein, is the material that stores hereditary information

11 The Hershey-Chase Experiments

12 Fig. 13-3a, p. 205

13 Fig. 13-3b, p. 205

14 Virus particle coat proteins labeled with 35 S 35 S remains outside cells DNA being injected into bacterium B In one experiment, bacteria were infected with virus particles labeled with a radioisotope of sulfur ( 35 S). The sulfur had labeled only viral proteins. The viruses were dislodged from the bacteria by whirling the mixture in a kitchen blender. Most of the radioactive sulfur was detected in the viruses, not in the bacterial cells. The viruses had not injected protein into the bacteria. Fig. 13-3b, p. 205

15 Fig. 13-3c, p. 205

16 Virus DNA labeled with 32 P Labeled DNA being injected into bacterium 32 P remains inside cells C In another experiment, bacteria were infected with virus particles labeled with a radioisotope of phosphorus ( 32 P). The phosphorus had labeled only viral DNA. When the viruses were dislodged from the bacteria, the radioactive phosphorus was detected mainly inside the bacterial cells. The viruses had injected DNA into the cells evidence that DNA is the genetic material of this virus. Fig. 13-3c, p. 205

17 Virus particle coat proteins labeled with 35 S 35 S remains outside cells DNA being injected into bacterium Virus DNA labeled with 32 P Labeled DNA being injected into bacterium 32 P remains inside cells Stepped Art Fig. 13-3, p. 205

18 Animation: Hershey-Chase experiments

19 13.1 Key Concepts Discovery of DNA s Function The work of many scientists over more than a century led to the discovery that DNA is the molecule that stores hereditary information about traits

20 13.2 The Discovery of DNA s Structure Watson and Crick s discovery of DNA s structure was based on almost fifty years of research by other scientists

21 DNA s Building Blocks Nucleotide A nucleic acid monomer consisting of a fivecarbon sugar (deoxyribose), three phosphate groups, and one of four nitrogen-containing bases DNA consists of four nucleotide building blocks Two pyrimidines: thymine and cytosine Two purines: adenine and guanine

22 Four Kinds of Nucleotides in DNA

23 adenine (A) deoxyadenosine triphosphate, a purine Fig. 13-4a, p. 206

24 guanine (G) deoxyguanosine triphosphate, a purine Fig. 13-4b, p. 206

25 thymine (T) deoxythymidine triphosphate, a pyrimidine Fig. 13-4c, p. 206

26 cytosine (C) deoxycytidine triphosphate, a pyrimidine Fig. 13-4d, p. 206

27 Chargaff s Rules The amounts of thymine and adenine in DNA are the same, and the amounts of cytosine and guanine are the same: A = T and G = C The proportion of adenine and guanine differs among species

28 Franklin, Watson and Crick Rosalind Franklin s research in x-ray crystallography revealed the dimensions and shape of the DNA molecule: an alpha helix This was the final piece of information Watson and Crick needed to build their model of DNA

29 Watson and Crick s DNA Model A DNA molecule consists of two nucleotide chains (strands), running in opposite directions and coiled into a double helix Base pairs form on the inside of the helix, held together by hydrogen bonds (A-T and G-C)

30 Patterns of Base Pairing Bases in DNA strands can pair in only one way A always pairs with T; G always pairs with C The sequence of bases is the genetic code Variation in base sequences gives life diversity

31 Structure of DNA

32 Fig. 13-5a, p. 207

33 2-nanometer diameter 0.34 nanometer between each base pair 3.4-nanometer length of each full twist of the double helix The numbers indicate the carbon of the ribose sugars (compare Figure 13.4). The 3 carbon of each sugar is joined by the phosphate group to the 5 carbon of the next sugar. These links form each strand s sugar phosphate backbone. The two sugar phosphate backbones run in parallel but opposite directions (green arrows). Think of one strand as upside down compared with the other. Fig. 13-5b, p. 207

34 Animation: DNA close up

35 13.2 Key Concepts Discovery of DNA s Structure A DNA molecule consists of two long chains of nucleotides coiled into a double helix Four kinds of nucleotides make up the chains, which are held together along their length by hydrogen bonds

36 13.3 DNA Replication and Repair A cell copies its DNA before mitosis or meiosis I DNA repair mechanisms and proofreading correct most replication errors

37 Semiconservative DNA Replication Each strand of a DNA double helix is a template for synthesis of a complementary strand of DNA One template builds DNA continuously; the other builds DNA discontinuously, in segments Each new DNA molecule consist of one old strand and one new strand

38 Enzymes of DNA Replication DNA helicase Breaks hydrogen bonds between DNA strands DNA polymerase Joins free nucleotides into a new strand of DNA DNA ligase Joins DNA segments on discontinuous strand

39 DNA Replication

40 adenine (A) deoxyadenosine triphosphate, a purine Fig. 13-4a, p. 206

41 guanine (G) deoxyguanosine triphosphate, a purine Fig. 13-4b, p. 206

42 thymine (T) deoxythymidine triphosphate, a pyrimidine Fig. 13-4c, p. 206

43 cytosine (C) deoxycytidine triphosphate, a pyrimidine Fig. 13-4d, p. 206

44 A A DNA molecule is double-stranded. The two strands of DNA stay zippered up together because they are complementary: their nucleotides match up according to base-pairing rules (G to C, T to A). B As replication starts, the two strands of DNA are unwound. In cells, the unwinding occurs simultaneously at many sites along the length of each double helix. C Each of the two parent strands serves as a template for assembly of a new DNA strand from free nucleotides, according to base-pairing rules (G to C, T to A). Thus, the two new DNA strands are complementary in sequence to the parental strands. D DNA ligase seals any gaps that remain between bases of the new DNA, so a continuous strand forms. The base sequence of each half-old, half-new DNA molecule is identical to that of the parent DNA molecule. Stepped Art Fig. 13-6, p. 208

45 Animation: DNA replication details

46 Semiconservative Replication of DNA

47 Discontinuous Synthesis of DNA

48 A Each DNA strand has two ends: one with a 5 carbon, and one with a 3 carbon. DNA polymerase can add nucleotides only at the 3 carbon. In other words, DNA synthesis proceeds only in the 5 to 3 direction. Fig. 13-8a, p. 209

49 Only one new DNA strand is assembled continuously The parent DNA double helix unwinds in this direction. The other new DNA strand is assembled in many pieces. Gaps are sealed by 3 5 DNA ligase. 3 5 B Because DNA synthesis proceeds only in the 5 to 3 direction, only one of the two new DNA strands can be assembled in a single piece. The other new DNA strand forms in short segments, which are called Okazaki fragments after the two scientists who discovered them. DNA ligase joins the fragments into a continuous strand of DNA. Fig. 13-8b, p. 209

50 Checking for Mistakes DNA repair mechanisms DNA polymerases proofread DNA sequences during DNA replication and repair damaged DNA When proofreading and repair mechanisms fail, an error becomes a mutation a permanent change in the DNA sequence

51 13.3 Key Concepts How Cells Duplicate Their DNA Before a cell begins mitosis or meiosis, enzymes and other proteins replicate its chromosome(s) Newly forming DNA strands are monitored for errors Uncorrected errors may become mutations

52 13.4 Using DNA to Duplicate Existing Mammals Reproductive cloning is a reproductive intervention that results in an exact genetic copy of an adult individual

53 Cloning Clones Exact copies of a molecule, cell, or individual Occur in nature by asexual reproduction or embryo splitting (identical twins) Reproductive cloning technologies produce an exact copy (clone) of an individual

54 Reproductive Cloning Technologies Somatic cell nuclear transfer (SCNT) Nuclear DNA of an adult is transferred to an enucleated egg Egg cytoplasm reprograms differentiated (adult) DNA to act like undifferentiated (egg) DNA The hybrid cell develops into an embryo that is genetically identical to the donor individual

55 Somatic Cell Nuclear Transfer (SCNT)

56 Fig. 13-9a, p. 210

57 A A cow egg is held in place by suction through a hollow glass tube called a micropipette. The polar body (Section 10.5) and chromosomes are identified by a purple stain. Fig. 13-9a, p. 210

58 Fig. 13-9b, p. 210

59 B A micropipette punctures the egg and sucks out the polar body and all of the chromosomes. All that remains inside the egg s plasma membrane is cytoplasm. Fig. 13-9b, p. 210

60 Fig. 13-9c, p. 210

61 C A new micropipette prepares to enter the egg at the puncture site. The pipette contains a cell grown from the skin of a donor animal. skin cell Fig. 13-9c, p. 210

62 Fig. 13-9d, p. 210

63 D The micropipette enters the egg and delivers the skin cell to a region between the cytoplasm and the plasma membrane. Fig. 13-9d, p. 210

64 Fig. 13-9e, p. 210

65 E After the pipette is withdrawn, the donor s skin cell is visible next to the cytoplasm of the egg. The transfer is complete. Fig. 13-9e, p. 210

66 Fig. 13-9f, p. 210

67 F The egg is exposed to an electric current. This treatment causes the foreign cell to fuse with and empty its nucleus into the cytoplasm of the egg. The egg begins to divide, and an embryo forms. After a few days, the embryo may be transplanted into a surrogate mother. Fig. 13-9f, p. 210

68 A Clone Produced by SCNT

69 Fig , p. 211

70 Animation: How Dolly was created

71 Therapeutic Cloning Therapeutic cloning uses SCNT to produce human embryos for research purposes Researchers harvest undifferentiated (stem) cells from the cloned human embryos

72 13.4 Key Concepts Cloning Animals Knowledge about the structure and function of DNA is the basis of several methods of making clones, which are identical copies of organisms

73 13.5 Fame and Glory In science, as in other professions, public recognition does not always include everyone who contributed to a discovery Rosalind Franklin was first to discover the molecular structure of DNA, but did not share in the Nobel prize which was given to Watson, Crick, and Wilkins

74 Rosalind Franklin s X-Ray Diffraction Image Franklin died of cancer at age 37, possibly related to extensive exposure to x-rays

75 13.5 Key Concepts The Franklin Footnote Science proceeds as a joint effort; many scientists contributed to the discovery of DNA s structure

76 Animation: DNA replication

77 Animation: Semidiscontinuous DNA replication

78 Animation: Structure of DNA

79 Animation: Subunits of DNA

80 ABC video: DNA ark promise hope for the future

81 Video: Goodbye, dolly