Ch8 microbial genetics

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Ch8 microbial genetics

  1. 1. Copyright © 2010 Pearson Education, Inc. CH8: Microbial Genetics  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?
  2. 2. 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 Structure and Function of Genetic Material
  3. 3. Copyright © 2010 Pearson Education, Inc. Terminology  Genomics: The molecular study of genomes (sequencing and molecular characterization of genomes).  Genotype: The genes of an organism  Phenotype: Expression of the genes
  4. 4. Copyright © 2010 Pearson Education, Inc. Figure 8.2 The Flow of Genetic Information
  5. 5. 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
  6. 6. Copyright © 2010 Pearson Education, Inc. Figure 8.3a Semiconservative Replication
  7. 7. Copyright © 2010 Pearson Education, Inc. Figure 8.4 DNA Synthesis
  8. 8. 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
  9. 9. Copyright © 2010 Pearson Education, Inc. Figure 8.5 DNA Synthesis
  10. 10. Copyright © 2010 Pearson Education, Inc. Figure 8.6 Replication of Bacterial DNA
  11. 11. Copyright © 2010 Pearson Education, Inc. Table 8.1 Important Enzymes DNA Gyrase DNA Helicase DNA polymerase
  12. 12. Copyright © 2010 Pearson Education, Inc. Table 8.1
  13. 13. Copyright © 2010 Pearson Education, Inc. RNA and Protein Synthesis 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
  14. 14. Copyright © 2010 Pearson Education, Inc. Figure 8.7 Transcription
  15. 15. Copyright © 2010 Pearson Education, Inc. Figure 8.7 The Process of Transcription
  16. 16. Copyright © 2010 Pearson Education, Inc. Figure 8.7 ANIMATION Transcription: Overview ANIMATION Transcription: Process The Process of Transcription
  17. 17. Copyright © 2010 Pearson Education, Inc. Figure 8.11 RNA Processing in Eukaryotes
  18. 18. 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
  19. 19. Copyright © 2010 Pearson Education, Inc. Figure 8.2 The Genetic Code  64 total codons of which 61 sense codons encode the 20 amino acids  3 are non-sense codons or stop codons.  The genetic code is degenerate  tRNA carries the complementary anticodon
  20. 20. Copyright © 2010 Pearson Education, Inc. Figure 8.8 The Genetic Code
  21. 21. Copyright © 2010 Pearson Education, Inc. Figure 8.10 Simultaneous Transcription & Translation
  22. 22. Copyright © 2010 Pearson Education, Inc. Figure 8.9-1
  23. 23. Copyright © 2010 Pearson Education, Inc. Figure 8.9-2
  24. 24. Copyright © 2010 Pearson Education, Inc. Regulation  Constitutive genes are expressed at a fixed rate (60-80%genes)  Other genes are expressed only as needed − Repressible genes: Always active , can be turned off (repressed). − Inducible genes: Inactive , needs to be turned on or induced. − Catabolite repression: Inhibition of the metabolism of alternative carbon sources by Glucose.  Regulation of protein synthesis saves (conserve) energy for the organism. The Regulation of Gene Expression
  25. 25. Copyright © 2010 Pearson Education, Inc. Figure 8.12 Operon Control of Transcription Consists of a promotor, an operator and series of genes
  26. 26. Copyright © 2010 Pearson Education, Inc. • Inducible operons – must be activated by inducers • Regulate catabolic pathway • Lactose Operon • Repressible operons – transcribed continually until deactivated by repressors • Regulate anabolic pathway. • Tryptophan Operon Operons
  27. 27. Copyright © 2010 Pearson Education, Inc. Figure 8.12 Induction
  28. 28. Copyright © 2010 Pearson Education, Inc. Figure 8.12 Induction
  29. 29. Copyright © 2010 Pearson Education, Inc. Figure 8.13 Repression
  30. 30. Copyright © 2010 Pearson Education, Inc. Figure 8.13 Repression
  31. 31. Copyright © 2010 Pearson Education, Inc.  Lactose present, no Glucose  Lactose + glucose present Figure 8.15 Catabolite Repression
  32. 32. Copyright © 2010 Pearson Education, Inc. Figure 8.14b
  33. 33. Copyright © 2010 Pearson Education, Inc. Mutation  A change in the genetic material  Mutation is a change in the base sequence of DNA.  Mutations may be neutral, beneficial, or harmful  Mutagen: Agent that causes mutations  Spontaneous mutations: Occur in the absence of a mutagen
  34. 34. 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
  35. 35. Copyright © 2010 Pearson Education, Inc.  Nonsense mutation Mutation  Results in a nonsense codon Figure 8.17a, c
  36. 36. Copyright © 2010 Pearson Education, Inc. Mutation  Frameshift mutation  Insertion or deletion of one or more nucleotide pairs Figure 8.17a, d
  37. 37. Copyright © 2010 Pearson Education, Inc.  Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes  Mutagens increase to one in 105 (10-5 ) or one in 103 (10–3) per replicated gene  Point mutations concept map The Frequency of Mutation
  38. 38. Copyright © 2010 Pearson Education, Inc. Figure 8.19a Chemical Mutagens Nucleoside analogs
  39. 39. Copyright © 2010 Pearson Education, Inc. Chemical mutagens  Frameshift mutagens  Cause small deletions or insertions  Ex:Benzopyrene in smoke  Aflatoxins  Acridine orange  Frameshift mutagens are often carcinogens.
  40. 40. 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  Causes physical breakdown of DNA
  41. 41. Copyright © 2010 Pearson Education, Inc. Figure 8.20 Radiation  UV radiation causes thymine dimers
  42. 42. Copyright © 2010 Pearson Education, Inc. Figure 8.20 Repair  Photolyases separate thymine dimers  Nucleotide excision repair (can repair other mutations also)
  43. 43. 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
  44. 44. Copyright © 2010 Pearson Education, Inc. Figure 8.21 Replica Plating
  45. 45. Copyright © 2010 Pearson Education, Inc. Figure 8.22 Ames Test for Chemical Carcinogens 90% of the chemicals found to be mutagenic also have been shown to be carcinogenic.
  46. 46. Copyright © 2010 Pearson Education, Inc. • Exchange of DNA segments composed of homologous sequences • Recombinants – cells with DNA molecules that contain new nucleotide sequences • Vertical gene transfer – organisms replicate their genomes and provide copies to descendants • Horizontal gene transfer – donor contributes part of genome to recipient; three types • Transformation • Transduction • Bacterial Conjugation Genetic Recombination and Transfer
  47. 47. 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. Genetic Recombination
  48. 48. 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
  49. 49. Copyright © 2010 Pearson Education, Inc. Figure 8.24 Genetic Transformation Griffith’s Experiment
  50. 50. Copyright © 2010 Pearson Education, Inc. • Griffiths experiment concluded transforming agent was DNA; one of conclusive pieces of proof that DNA is genetic material • Cells that take up DNA are competent; results from alterations in cell wall and cytoplasmic membrane that allow DNA to enter cell Transformation
  51. 51. Copyright © 2010 Pearson Education, Inc. Figure 8.26 Bacterial Conjugation Transfer of DNA by cell to cell contact
  52. 52. Copyright © 2010 Pearson Education, Inc. Figure 8.28 Transduction by a Bacteriophage • Generalized transduction – transducing phage carries random DNA segment from donor to recipient • Specialized transduction – only certain donor DNA sequences are transferred
  53. 53. 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  Bacteriocins plasmids  R factors: Encode antibiotic resistance
  54. 54. Copyright © 2010 Pearson Education, Inc. Figure 8.29 R Factor, a Type of Plasmid Carry genes that confer resistance to antibiotics.
  55. 55. 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
  56. 56. Copyright © 2010 Pearson Education, Inc. Genes and Evolution  Mutations and recombination provide diversity  Fittest organisms for an environment are selected by natural selection

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