1. Copyright © 2010 Pearson Education, Inc. Lectures prepared by Christine L. Case Chapter 8 Microbial Genetics

2. Copyright © 2010 Pearson Education, Inc. Q&A  E. coli is found naturally in the human large intestine, and there it is beneficial. However, the strain designated E. coli O157:H7 produces Shiga toxin. How did E. coli acquire this gene from Shigella?

3. Copyright © 2010 Pearson Education, Inc. Structure and Function of Genetic Material 8-1Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics. 8-2Describe how DNA serves as genetic information. 8-3Describe the process of DNA replication. 8-4Describe protein synthesis, including transcription, RNA processing, and translation. 8-5Compare protein synthesis in prokaryotes and eukaryotes. Learning Objectives

4. Copyright © 2010 Pearson Education, Inc. Terminology  Genetics: The study of what genes are, how they carry information, how information is expressed, and how genes are replicated  Gene: A segment of DNA that encodes a functional product, usually a protein  Chromosome: Structure containing DNA that physically carries hereditary information; the chromosomes contain the genes  Genome: All the genetic information in a cell

5. Copyright © 2010 Pearson Education, Inc. Terminology  Genomics: The molecular study of genomes  Genotype: The genes of an organism  Phenotype: Expression of the genes

6. Copyright © 2010 Pearson Education, Inc. Clinical Focus, p. 223 Determine Relatedness

7. Copyright © 2010 Pearson Education, Inc. Determine Relatedness Strain % Similar to Uganda Kenya71% U.S.51%  Which strain is more closely related to the Uganda strain?

8. Copyright © 2010 Pearson Education, Inc. Figure 8.1a E. coli

9. Copyright © 2010 Pearson Education, Inc. Figure 8.1b Genetic Map of the Chromosome of E. coli

10. Copyright © 2010 Pearson Education, Inc. Figure 8.2 The Flow of Genetic Information

11. Copyright © 2010 Pearson Education, Inc. Figure 8.3b DNA  Polymer of nucleotides: Adenine, thymine, cytosine, and guanine  Double helix associated with proteins  "Backbone" is deoxyribose-phosphate  Strands are held together by hydrogen bonds between AT and CG  Strands are antiparallel

12. Copyright © 2010 Pearson Education, Inc. Figure 8.3a Semiconservative Replication

13. Copyright © 2010 Pearson Education, Inc. Figure 8.4 DNA Synthesis

14. Copyright © 2010 Pearson Education, Inc. DNA Synthesis  DNA is copied by DNA polymerase  In the 5'  3' direction  Initiated by an RNA primer  Leading strand is synthesized continuously  Lagging strand is synthesized discontinuously  Okazaki fragments  RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase

15. Copyright © 2010 Pearson Education, Inc. Table 8.1

16. Copyright © 2010 Pearson Education, Inc. Table 8.1

17. Copyright © 2010 Pearson Education, Inc. Figure 8.5 DNA Synthesis

18. Copyright © 2010 Pearson Education, Inc. Figure 8.6 Replication of Bacterial DNA

19. Copyright © 2010 Pearson Education, Inc. ANIMATION DNA Replication: Replication Proteins ANIMATION DNA Replication: Overview ANIMATION DNA Replication: Forming the Replication Fork Replication of Bacterial DNA

20. Copyright © 2010 Pearson Education, Inc. Check Your Understanding Give a clinical application of genomics. 8-1 Why is the base pairing in DNA important? 8-2 Describe DNA replication, including the functions of DNA gyrase, DNA ligase, and DNA polymerase. 8-3

21. Copyright © 2010 Pearson Education, Inc. Transcription  DNA is transcribed to make RNA (mRNA, tRNA, and rRNA)  Transcription begins when RNA polymerase binds to the promoter sequence  Transcription proceeds in the 5'  3' direction  Transcription stops when it reaches the terminator sequence

22. Copyright © 2010 Pearson Education, Inc. Figure 8.7 Transcription

23. Copyright © 2010 Pearson Education, Inc. Figure 8.7 The Process of Transcription

24. Copyright © 2010 Pearson Education, Inc. Figure 8.7 ANIMATION Transcription: Overview ANIMATION Transcription: Process The Process of Transcription

25. Copyright © 2010 Pearson Education, Inc. Figure 8.11 RNA Processing in Eukaryotes

26. Copyright © 2010 Pearson Education, Inc. Figure 8.2 Translation  mRNA is translated in codons (three nucleotides)  Translation of mRNA begins at the start codon: AUG  Translation ends at nonsense codons: UAA, UAG, UGA

27. Copyright © 2010 Pearson Education, Inc. Figure 8.2 The Genetic Code  64 sense codons on mRNA encode the 20 amino acids  The genetic code is degenerate  tRNA carries the complementary anticodon

28. Copyright © 2010 Pearson Education, Inc. ANIMATION Translation: Overview ANIMATION Translation: Genetic Code ANIMATION Translation: Process The Genetic Code

29. Copyright © 2010 Pearson Education, Inc. Figure 8.8 The Genetic Code

30. Copyright © 2010 Pearson Education, Inc. Figure 8.10 Simultaneous Transcription & Translation

31. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

32. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

33. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

34. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

35. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

36. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

37. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

38. Copyright © 2010 Pearson Education, Inc. Figure 8.9 The Process of Translation

39. Copyright © 2010 Pearson Education, Inc. Check Your Understanding What is the role of the promoter, terminator, and mRNA in transcription? 8-4 How does mRNA production in eukaryotes differ from the process in prokaryotes? 8-5

40. Copyright © 2010 Pearson Education, Inc. The Regulation of Gene Expression 8-6Define operon. 8-7Explain the regulation of gene expression in bacteria by induction, repression, and catabolite repression. Learning Objectives

41. Copyright © 2010 Pearson Education, Inc. Regulation  Constitutive genes are expressed at a fixed rate  Other genes are expressed only as needed  Repressible genes  Inducible genes  Catabolite repression

42. Copyright © 2010 Pearson Education, Inc. Figure 8.12 ANIMATION Operons: Overview Operon

43. Copyright © 2010 Pearson Education, Inc. Figure 8.12 Induction

44. Copyright © 2010 Pearson Education, Inc. Figure 8.12 Induction

45. Copyright © 2010 Pearson Education, Inc. Figure 8.13 Repression

46. Copyright © 2010 Pearson Education, Inc. Figure 8.13 ANIMATION Operons: Induction ANIMATION Operons: Repression Repression

47. Copyright © 2010 Pearson Education, Inc. Figure 8.14 (a) Growth on glucose or lactose alone (b) Growth on glucose and lactose combined Catabolite Repression

48. Copyright © 2010 Pearson Education, Inc.  Lactose present, no glucose  Lactose + glucose present Figure 8.15

49. Copyright © 2010 Pearson Education, Inc. Check Your Understanding What is an operon? 8-6 What is the role of cAMP in catabolite repression? 8-7

50. Copyright © 2010 Pearson Education, Inc. Mutation: Change in the Genetic Material 8-8Classify mutations by type. 8-9Define mutagen. 8-10Describe two ways mutations can be repaired. 8-11Describe the effect of mutagens on the mutation rate. 8-12Outline the methods of direct and indirect selection of mutants. 8-13Identify the purpose of and outline the procedure for the Ames test. Learning Objectives

51. Copyright © 2010 Pearson Education, Inc. Mutation  A change in the genetic material  Mutations may be neutral, beneficial, or harmful  Mutagen: Agent that causes mutations  Spontaneous mutations: Occur in the absence of a mutagen

52. Copyright © 2010 Pearson Education, Inc.  Base substitution (point mutation)  Missense mutation Mutation  Change in one base  Result in change in amino acid Figure 8.17a, b

53. Copyright © 2010 Pearson Education, Inc.  Nonsense mutation Mutation  Results in a nonsense codon Figure 8.17a, c

54. Copyright © 2010 Pearson Education, Inc. Mutation  Frameshift mutation  Insertion or deletion of one or more nucleotide pairs Figure 8.17a, d

55. Copyright © 2010 Pearson Education, Inc.  Spontaneous mutation rate = 1 in 10 9 replicated base pairs or 1 in 10 6 replicated genes  Mutagens increase to 10 –5 or 10 –3 per replicated gene ANIMATION Mutations: Types The Frequency of Mutation

56. Copyright © 2010 Pearson Education, Inc. Figure 8.19a Chemical Mutagens

57. Copyright © 2010 Pearson Education, Inc. Figure 8.19b ANIMATION Mutagens Chemical Mutagens

58. Copyright © 2010 Pearson Education, Inc. Radiation  Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone

59. Copyright © 2010 Pearson Education, Inc. Figure 8.20 Radiation  UV radiation causes thymine dimers

60. Copyright © 2010 Pearson Education, Inc. Figure 8.20 Repair  Photolyases separate thymine dimers  Nucleotide excision repair ANIMATION Mutations: Repair

61. Copyright © 2010 Pearson Education, Inc. Selection  Positive (direct) selection detects mutant cells because they grow or appear different  Negative (indirect) selection detects mutant cells because they do not grow  Replica plating

62. Copyright © 2010 Pearson Education, Inc. Figure 8.21 Replica Plating

63. Copyright © 2010 Pearson Education, Inc. Figure 8.22 Ames Test for Chemical Carcinogens

64. Copyright © 2010 Pearson Education, Inc. Figure 8.22 Ames Test for Chemical Carcinogens

65. Copyright © 2010 Pearson Education, Inc. Check Your Understanding How can a mutation be beneficial? 8-8 How are mutations caused by chemicals? By radiation? 8-9 How can mutations be repaired? 8-10 How do mutagens affect the mutation rate? 8-11 How would you isolate an antibiotic-resistant bacterium? An antibiotic-sensitive bacterium? 8-12 What is the principle behind the Ames test? 8-13

66. Copyright © 2010 Pearson Education, Inc. Genetic Transfer and Recombination 8-14Differentiate horizontal and vertical gene transfer. 8-15Compare the mechanisms of genetic recombination in bacteria. 8-16Describe the functions of plasmids and transposons. Learning Objectives

67. Copyright © 2010 Pearson Education, Inc.  Vertical gene transfer: Occurs during reproduction between generations of cells.  Horizontal gene transfer: The transfer of genes between cells of the same generation. ANIMATION Horizontal Gene Transfer: Overview Genetic Recombination

68. Copyright © 2010 Pearson Education, Inc. Figure 8.23 Genetic Recombination  Exchange of genes between two DNA molecules  Crossing over occurs when two chromosomes break and rejoin

69. Copyright © 2010 Pearson Education, Inc. Figure 8.25 Genetic Recombination

70. Copyright © 2010 Pearson Education, Inc. Figure 8.24 ANIMATION Transformation Genetic Transformation

71. Copyright © 2010 Pearson Education, Inc. Figure 8.26 Bacterial Conjugation

72. Copyright © 2010 Pearson Education, Inc. Figure 8.27a Conjugation in E. coli

73. Copyright © 2010 Pearson Education, Inc. Figure 8.27b Conjugation in E. coli

74. Copyright © 2010 Pearson Education, Inc. Figure 8.27c ANIMATION Hfr Conjugation ANIMATION Chromosome MappingANIMATION F Factor ANIMATION Conjugation: Overview Conjugation in E. coli

75. Copyright © 2010 Pearson Education, Inc. ANIMATION Generalized Transduction Figure 8.28 ANIMATION Specialized Transduction Transduction by a Bacteriophage

76. Copyright © 2010 Pearson Education, Inc. Q&A  E. coli is found naturally in the human large intestine, and there it is beneficial. However, the strain designated E. coli O157:H7 produces Shiga toxin. How did E. coli acquire this gene from Shigella?

77. Copyright © 2010 Pearson Education, Inc. Plasmids  Conjugative plasmid: Carries genes for sex pili and transfer of the plasmid  Dissimilation plasmids: Encode enzymes for catabolism of unusual compounds  R factors: Encode antibiotic resistance

78. Copyright © 2010 Pearson Education, Inc. Figure 8.29 R Factor, a Type of Plasmid

79. Copyright © 2010 Pearson Education, Inc. Figure 8.30a, b Transposons  Segments of DNA that can move from one region of DNA to another  Contain insertion sequences for cutting and resealing DNA (transposase)  Complex transposons carry other genes

80. Copyright © 2010 Pearson Education, Inc. Figure 8.30c Transposons

81. Copyright © 2010 Pearson Education, Inc. ANIMATION Transposons: Complex Transposons ANIMATION Transposons: Insertion Sequences ANIMATION Transposons: Overview Transposons

82. Copyright © 2010 Pearson Education, Inc. Check Your Understanding Differentiate horizontal and vertical gene transfer. 8-14 Compare conjugation between the following pairs: F +  F –, Hfr  F –. 8-15 What types of genes do plasmids carry? 8-16

83. Copyright © 2010 Pearson Education, Inc. Genes and Evolution 8-17Discuss how genetic mutation and recombination provide material for natural selection to act upon. Learning Objective

84. Copyright © 2010 Pearson Education, Inc. Genes and Evolution  Mutations and recombination provide diversity  Fittest organisms for an environment are selected by natural selection

85. Copyright © 2010 Pearson Education, Inc. Clinical Focus, p. 223 Evolution

86. Copyright © 2010 Pearson Education, Inc. Evolution Strain % Similar to Uganda Kenya71% U.S.51%  Which strain is more closely related to the Uganda strain?  How did the virus change?

87. Copyright © 2010 Pearson Education, Inc. Check Your Understanding Natural selection means that the environment favors survival of some genotypes. From where does diversity in genotypes come? 8-17