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DNA: The Carrier of Genetic Information DNA: The Carrier of Genetic Information Chapter 12.

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Presentation on theme: "DNA: The Carrier of Genetic Information DNA: The Carrier of Genetic Information Chapter 12."— Presentation transcript:

1 DNA: The Carrier of Genetic Information DNA: The Carrier of Genetic Information Chapter 12

2 Learning Objective 1 What evidence was accumulated during the 1940s and early 1950s demonstrating that DNA is the genetic material? What evidence was accumulated during the 1940s and early 1950s demonstrating that DNA is the genetic material?

3 The Mystery of Genes Many early geneticists thought genes were proteins Many early geneticists thought genes were proteins Proteins are complex and variable Proteins are complex and variable Nucleic acids are simple molecules Nucleic acids are simple molecules

4 Evidence for DNA DNA (deoxyribonucleic acid) DNA (deoxyribonucleic acid) Transformation experiments Transformation experiments DNA of one strain of bacteria can transfer genetic characteristics to related bacteria DNA of one strain of bacteria can transfer genetic characteristics to related bacteria

5 Bacteriophage Experiments Bacteriophage (virus) infects bacterium Bacteriophage (virus) infects bacterium only DNA from virus enters the cell only DNA from virus enters the cell virus reproduces and forms new viral particles from DNA alone virus reproduces and forms new viral particles from DNA alone

6 KEY CONCEPTS Beginning in the 1920s, evidence began to accumulate that DNA is the hereditary material Beginning in the 1920s, evidence began to accumulate that DNA is the hereditary material

7 Learning Objective 2 What questions did these classic experiments address? What questions did these classic experiments address? Griffith’s transformation experiment Griffith’s transformation experiment Avery’s contribution to Griffith’s work Avery’s contribution to Griffith’s work Hershey–Chase experiments Hershey–Chase experiments

8 Griffith’s Transformation Experiment Can a genetic trait be transmitted from one bacterial strain to another? Can a genetic trait be transmitted from one bacterial strain to another? Answer: Yes Answer: Yes

9 Griffith’s Transformation Experiment

10 Fig. 12-1, p. 261 Experiment 1Experiment 2Experiment 3 Experiment 4 R cells injected S cells injected Heat-killed S cells injected R cells and heat- killed S cells injected Mouse lives Mouse diesMouse lives Mouse dies

11 Animation: Griffith’s Experiment CLICK TO PLAY

12 Avery’s Experiments What molecule is responsible for bacterial transformation? What molecule is responsible for bacterial transformation? Answer: DNA Answer: DNA

13 Hershey–Chase Experiments Is DNA or protein the genetic material in bacterial viruses (phages)? Is DNA or protein the genetic material in bacterial viruses (phages)? Answer: DNA Answer: DNA

14 Hershey–Chase Experiments

15 Fig. 12-2, p S Bacterial viruses grown in 35 S to label protein coat or 32 P to label DNA 32 P Viruses infect bacteria 1 2

16 Fig. 12-2, p. 262 Agitate cells in blender Separate by centrifugation 35 S 32 P Bacteria in pellet contain 32 P- labeled DNA 35 S-labeled protein in supernatant 3 4 5

17 Fig. 12-2, p. 262 Viral reproduction inside bacterial cells from pellet 7 32 P Cell lysis

18 Learning Objective 3 How do nucleotide subunits link to form a single DNA strand? How do nucleotide subunits link to form a single DNA strand?

19 Watson and Crick DNA Model DNA Model Demonstrated Demonstrated how information is stored in molecule’s structure how information is stored in molecule’s structure how DNA molecules are templates for their own replication how DNA molecules are templates for their own replication

20 Nucleotides DNA is a polymer of nucleotides DNA is a polymer of nucleotides Each nucleotide subunit contains Each nucleotide subunit contains a nitrogenous base a nitrogenous base purines (adenine or guanine) purines (adenine or guanine) pyrimidines (thymine or cytosine) pyrimidines (thymine or cytosine) a pentose sugar (deoxyribose) a pentose sugar (deoxyribose) a phosphate group a phosphate group

21 Forming DNA Chains Backbone Backbone alternating sugar and phosphate groups alternating sugar and phosphate groups joined by covalent phosphodiester linkages joined by covalent phosphodiester linkages Phosphate group attaches to Phosphate group attaches to 5′ carbon of one deoxyribose 5′ carbon of one deoxyribose 3′ carbon of the next deoxyribose 3′ carbon of the next deoxyribose

22 DNA Nucleotides

23 Fig. 12-3, p. 264 Thymine Adenine Nucleotide Cytosine Phosphate group Phosphodiester linkage Guanine Deoxyribose (sugar)

24 Animation: Subunits of DNA CLICK TO PLAY

25 KEY CONCEPTS The DNA building blocks consist of four nucleotide subunits: T, C, A, and G The DNA building blocks consist of four nucleotide subunits: T, C, A, and G

26 Learning Objective 4 How are the two strands of DNA oriented with respect to each other? How are the two strands of DNA oriented with respect to each other?

27 DNA Molecule 2 polynucleotide chains 2 polynucleotide chains associated as double helix associated as double helix

28 DNA Molecule

29 Fig. 12-5, p. 266 Sugar–phosphate backbone Minor groove 3.4 nm Major groove 0.34 nm 2.0 nm = hydrogen = oxygen = carbon = atoms in base pairs= phosphorus

30 Double Helix Antiparallel Antiparallel chains run in opposite directions chains run in opposite directions 5′ end 5′ end phosphate attached to 5′ deoxyribose carbon phosphate attached to 5′ deoxyribose carbon 3′ end 3′ end hydroxyl attached to 3′ deoxyribose carbon hydroxyl attached to 3′ deoxyribose carbon

31 KEY CONCEPTS The DNA molecule consists of two strands that wrap around each other to form a double helix The DNA molecule consists of two strands that wrap around each other to form a double helix The order of its building blocks stores genetic information The order of its building blocks stores genetic information

32 Animation: DNA Close Up CLICK TO PLAY

33 Learning Objective 5 What are the base-pairing rules for DNA? What are the base-pairing rules for DNA? How do complementary bases bind to each other? How do complementary bases bind to each other?

34 Base Pairs Hydrogen bonding Hydrogen bonding between specific base pairs between specific base pairs binds two chains of helix binds two chains of helix Adenine (A) with thymine (T) Adenine (A) with thymine (T) forms two hydrogen bonds forms two hydrogen bonds Guanine (G) with cytosine (C) Guanine (G) with cytosine (C) forms three hydrogen bonds forms three hydrogen bonds

35 Base Pairs and Hydrogen Bonds

36 Fig. 12-6a, p. 267

37 Fig. 12-6b, p. 267 AdenineThymine Deoxyribose GuanineCytosine Deoxyribose

38 Chargaff’s Rules Complementary base pairing Complementary base pairing between A and T; G and C between A and T; G and C therefore A = T; G = C therefore A = T; G = C If base sequence of 1 strand is known If base sequence of 1 strand is known base sequence of other strand can be predicted base sequence of other strand can be predicted

39 KEY CONCEPTS Nucleotide subunits pair, based on precise pairing rules: T pairs with A, and C pairs with G Nucleotide subunits pair, based on precise pairing rules: T pairs with A, and C pairs with G Hydrogen bonding between base pairs holds two strands of DNA together Hydrogen bonding between base pairs holds two strands of DNA together

40 Learning Objective 6 What evidence from Meselson and Stahl’s experiment enabled scientists to differentiate between semiconservative replication of DNA and alternative models? What evidence from Meselson and Stahl’s experiment enabled scientists to differentiate between semiconservative replication of DNA and alternative models?

41 Models of DNA Replication

42 Fig. 12-7a, p. 268 (a) Hypothesis 1: Semiconservative replication Parental DNAFirst generationSecond generation

43 Fig. 12-7b, p. 268 (b) Hypothesis 2: Conservative replication Parental DNAFirst generationSecond generation

44 Fig. 12-7c, p. 268 (c) Hypothesis 3: Dispersive replication Parental DNAFirst generationSecond generation

45 Meselson-Stahl Experiment E. coli E. coli grown in medium containing heavy nitrogen ( 15 N) grown in medium containing heavy nitrogen ( 15 N) incorporated 15 N into DNA incorporated 15 N into DNA Transferred from 15 N to 14 N medium Transferred from 15 N to 14 N medium after one or two generations, DNA density supported semiconservative replication after one or two generations, DNA density supported semiconservative replication

46 Meselson-Stahl Experiment

47 Fig. 12-8a, p. 269 Bacteria are grown in 15 N (heavy) medium. All DNA is heavy. Some cells are transferred to 14 N (light) medium. Some cells continue to grow in 14 N medium. First generationSecond generation Cesium chloride (CsCl) High density Low density DNA DNA is mixed with CsCl solution, placed in an ultracentrifuge, and centrifuged at very high speed for about 48 hours. 14 N (light) DNA 14 N – 15 N hybrid DNA 15 N (heavy) DNA DNA molecules move to positions where their density equals that of the CsCl solution. The greater concentration of CsCl at the bottom of the tube is due to sedimentation under centrifigal force.

48 Fig. 12-8b, p N (light) DNA 14 N – 15 N hybrid DNA 15 N (heavy) DNA Before transfer to 14 N One cell generation after transfer to 14 N Two cell generations after transfer to 14 N The location of DNA molecules within the centrifuge tube can be determined by UV optics. DNA solutions absorb strongly at 260 nm.

49 Semiconservative Replication Each daughter double helix consists of Each daughter double helix consists of 1 original strand from parent molecule 1 original strand from parent molecule 1 new complementary strand 1 new complementary strand

50 Learning Objective 7 How does DNA replicate? How does DNA replicate? What are some unique features of the process? What are some unique features of the process?

51 DNA Replication 2 strands of double helix unwind 2 strands of double helix unwind each is template for complementary strand each is template for complementary strand Replication is initiated Replication is initiated DNA primase synthesizes RNA primer DNA primase synthesizes RNA primer DNA strand grows DNA strand grows DNA polymerase adds nucleotide subunits DNA polymerase adds nucleotide subunits

52 DNA Replication

53 Fig , p. 271 Nucleotide joined to growing chain by DNA polymerase Phosphates released Base

54 Other Enzymes DNA helicases DNA helicases open the double helix open the double helix Topoisomerases Topoisomerases prevent tangling and knotting prevent tangling and knotting

55 KEY CONCEPTS DNA replication results in two identical double-stranded DNA molecules DNA replication results in two identical double-stranded DNA molecules molecular mechanism passes genetic information from one generation to the next molecular mechanism passes genetic information from one generation to the next

56 Learning Objective 8 What makes DNA replication (a) bidirectional and (b) continuous in one strand and discontinuous in the other? What makes DNA replication (a) bidirectional and (b) continuous in one strand and discontinuous in the other?

57 Bidirectional Replication Starting at origin of replication Starting at origin of replication proceeding in both directions proceeding in both directions Eukaryotic chromosome Eukaryotic chromosome may have multiple origins of replication may have multiple origins of replication may replicate at many points at same time may replicate at many points at same time

58 Bidirectional Replication

59 Fig a, p. 272 DNA polymerase Origin of replication on DNA molecule 3’ 5’ 3’ 5’

60 Fig b, p. 272 Twist introduced into the helix by unwinding Single-strand binding proteins RNA primer DNA polymerase DNA helicase RNA primer Direction of replication 3’ 5’ 3’ 5’ 3’

61 Fig c, p ’ 5’ 3’ 5’ 3’ 5’ 3’ 5’

62 DNA Synthesis Always proceeds in 5′ → 3′ direction Always proceeds in 5′ → 3′ direction Leading strand Leading strand synthesized continuously synthesized continuously Lagging strand Lagging strand synthesized discontinuously synthesized discontinuously forms short Okazaki fragments forms short Okazaki fragments DNA primase synthesizes RNA primers DNA primase synthesizes RNA primers DNA ligase links Okazaki fragments DNA ligase links Okazaki fragments

63 DNA Synthesis

64 Fig a, p. 273 DNA helix RNA primer Leading strand DNA polymerase Lagging strand (first Okazaki fragment) Direction of replication Replication fork 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’

65 Fig b, p. 273 Leading strand RNA primers Two Okazaki fragments 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’

66 Fig c, p. 273 Leading strand DNA ligase Third Okazaki fragment Lagging strand 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’

67 Replication in Bacteria and Eukaryotes

68 Fig a, p. 274 Template DNA (light blue) New DNA (dark blue) 3’ 5’ 3’ 5’

69 Fig b, p nm

70 Fig c, p. 274 Replication “bubbles” Single replication bubble formed from two merged bubbles Replication fork 3’ 5’ 3’ 5’

71 Animation: Overview of DNA replication and base pairing CLICK TO PLAY

72 Learning Objective 9 How do enzymes proofread and repair errors in DNA? How do enzymes proofread and repair errors in DNA?

73 DNA Polymerases Proofread each new nucleotide Proofread each new nucleotide against template nucleotide against template nucleotide Find errors in base pairing Find errors in base pairing remove incorrect nucleotide remove incorrect nucleotide insert correct one insert correct one

74 DNA Mutation

75 Fig. 12-9, p. 270 Mutation

76 Stepped Art Fig. 12-9, p. 270 Mutation

77 Mismatch Repair Enzymes recognize incorrectly paired nucleotides and remove them Enzymes recognize incorrectly paired nucleotides and remove them DNA polymerases fill in missing nucleotides DNA polymerases fill in missing nucleotides

78 Nucleotide Excision Repair Repairs DNA lesions Repairs DNA lesions caused by sun or harmful chemicals caused by sun or harmful chemicals 3 enzymes 3 enzymes nuclease cuts out damaged DNA nuclease cuts out damaged DNA DNA polymerase adds correct nucleotides DNA polymerase adds correct nucleotides DNA ligase closes breaks in sugar–phosphate backbone DNA ligase closes breaks in sugar–phosphate backbone

79 Nucleotide Excision Repair

80 Fig , p. 275 Nuclease enzyme bound to DNA DNA lesion DNA polymerase DNA ligase New DNA 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’

81 Learning Objective 10 What is a telomere? What is a telomere? What are the possible connections between telomerase and cell aging, and between telomerase and cancer? What are the possible connections between telomerase and cell aging, and between telomerase and cancer?

82 Telomeres Eukaryotic chromosome ends Eukaryotic chromosome ends noncoding, repetitive DNA sequences noncoding, repetitive DNA sequences Shorten slightly with each cell cycle Shorten slightly with each cell cycle Can be extended by telomerase Can be extended by telomerase

83 Replication at Telomeres

84 Fig a, p. 276 DNA replication RNA primer Removal of primer 3’ 5’ + +

85 Fig b, p ’ 5’

86 Cell Aging May be caused by absence of telomerase activity May be caused by absence of telomerase activity Cells lose ability to divide Cells lose ability to divide after a limited number of cell divisions after a limited number of cell divisions

87 Cancer Cells Have telomerase Have telomerase to maintain telomere length and possibly resist apoptosis to maintain telomere length and possibly resist apoptosis Including human cancers Including human cancers breast, lung, colon, prostate gland, pancreas breast, lung, colon, prostate gland, pancreas


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