Bacterial Genetics

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Bacterial Genetics

  1. 1. Bacterial Genetics Jaime A. Santos, MD,FPPS,FPIDSP Friday, October 9, 2009
  2. 2. Bacteria: Prokaryotes • nucleoid : not enclosed by nuclear membrane • most have one circular chromosome consisting of double-stranded DNA • single origin of bidirectional replication Friday, October 9, 2009
  3. 3. Plasmid plasmid chromosome Friday, October 9, 2009
  4. 4. DNA Structure Friday, October 9, 2009
  5. 5. DNA Replication Friday, October 9, 2009
  6. 6. Transcription Friday, October 9, 2009
  7. 7. Translation Friday, October 9, 2009
  8. 8. DNA Repair Friday, October 9, 2009
  9. 9. Mutation • definition: any change in the base sequence of DNA • single base change: transition (purine replaced by purine, pyrimidine replaced by pyrimidine) or transversion (purine replaced by pyrimidine or vice-versa) Friday, October 9, 2009
  10. 10. Mutation: effect on protein product • silent mutation: no change in amino acid in encoded protein • missense mutation: different amino acid in protein product • nonsense mutation: change results in stop codon e.g. TAG Friday, October 9, 2009
  11. 11. Mutation Friday, October 9, 2009
  12. 12. Transposons Friday, October 9, 2009
  13. 13. Genetic Exchange in Bacteria •Transformation •Transduction •Conjugation Friday, October 9, 2009
  14. 14. Genetic Exchange: Transformation • incorporation of exogenous or foreign DNA • competence - ability to interact with exogenous DNA • H. influenzae, S. pneumoniae, Neisseria Friday, October 9, 2009
  15. 15. Transformation Friday, October 9, 2009
  16. 16. Transformation Friday, October 9, 2009
  17. 17. Bacteriophages • viruses infecting bacteria • bacteriophage infection may result in lysis (by virulent phages) or lysogeny (by temperate phages) Friday, October 9, 2009
  18. 18. Bacteriophage: Lytic cycle Friday, October 9, 2009
  19. 19. Bacteriophage: Lysogeny Friday, October 9, 2009
  20. 20. Genetic exchange: Transduction • transfer of bacterial DNA from one cell to another by means of a bacteriophage infection Friday, October 9, 2009
  21. 21. Transduction: types • generalized transduction: random packaging of bacterial host cell DNA in phage capsid • specialized transduction: when prophage genome is excised it drags adjacent bacterial genes resulting in hybrid phage- bacterial genome Friday, October 9, 2009
  22. 22. Generalized Transduction Friday, October 9, 2009
  23. 23. Specialized Transduction Friday, October 9, 2009
  24. 24. Plasmids • self-replicating, circular, double- stranded DNA • carry genetic information for new bacterial properties e.g. virulence factors and antibiotic resistance • may transfer from 1 cell to another (conjugative plasmids) or may stay within bacterial cell Friday, October 9, 2009
  25. 25. Genetic exchange: conjugation • contact between F+ donor with sex pilus (coded by F plasmid) and F- recipient • unidirectional • starts from 5’ end • results in transfer of conjugative plasmid or plasmid with bacterial genes to which it is integrated Friday, October 9, 2009
  26. 26. Conjugation Friday, October 9, 2009
  27. 27. Conjugation Friday, October 9, 2009
  28. 28. What are the consequences of genetic exchange in bacteria? Friday, October 9, 2009
  29. 29. 28 Friday, October 9, 2009
  30. 30. Thank You! 28 Friday, October 9, 2009

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