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Microbial Genetics

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Microbial Genetics - PowerPoint PPT Presentation

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Microbial Genetics

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  1. Microbial Genetics

  2. Gene Transfer,Genetic Engineering,and Genomics 1.   Genetic recombination. 2.   Genetic engineering. 3. Microbial genomics.

  3. A. Genetic Terminology

  4. Genotype • The genetic compliment of an organism • Types of genotypic changes • Mutation • Conjugation • Transduction • Transformation

  5. Phenotype • The genetic expression of an organism • Types of phenotypic expressions • Morphology • Cultural • Physiological

  6. B. The Bacterial Chromosome

  7. Introduction DNA is arranged as a single molecule with no histones present, and with no dominance or recessiveness in the genes. Bacterial chromosome is located in the nucleoid. In E. coli there are 4000 genes spread over 1.5mm of DNA in less than 1 micrometer of space

  8. Loop domain structure allows for compaction of DNA

  9. Replication of the chromosome • DNA polymerase • The semiconservative method • Replication of a closed loop chromosome • Okazaki fragments • Rolling circle method

  10. Plasmids • Fragments of DNA in the cytoplasm • R Factors - confer drug resistance • Bacteriocins -proteins toxic to other bacteria and human cell • Many plasmids are found in Gram-Negative bacteria

  11. C. Bacterial Mutation

  12. Permanent alteration in the DNA Example: nonpathogenic Yersinia pestis have genes that cause them to remain in mid gut, pathogenic Y. pestis do not have these genes Types of mutations Spontaneous Induced

  13. Spontaneous mutations Occurs every 106 to 1010 replications 1 mutation in every billion bacteria Example: Neisseria gonorrhoeae penicillin resistance original mutation was spontaneous Example: Salmonella strains antibiotic resistance

  14. Induced mutations • Chemical or Physical agents enhance mutation rate • Mutagens • Ultraviolet light—mechanism of action • Chemicals • Chromosomal changes

  15. Mutation Type Point (substitution) (leu) (ser) (arg) Normal AAT AGT GCC (leu) (cyst) (arg) Mutant AAT TGT GCC

  16. Mutation Type Frameshift (deletion) (leu) (ser) (arg) Normal AAT AGT GCC (leu) (val)(pro) Mutant AAT AGTGCCA

  17. Mutation Type Frameshift (insertion) (leu) (ser) (arg) Normal AAT AGT GCC (leu) (glut)(cyst) Mutant AAT CAGTGCC

  18. Repair Mechanisms DNA repair enzymes Many enzymes Constantly checking for errors Repair mechanisms Mismatch repair “proofreads” Damage repair Excision repair Dimer repair (UV light)

  19. Mismatch Repair

  20. Excision Repair

  21. Transposable genetic elements • Insertion sequences • Small DNA segments • Provide no genetic information • Located at several places on the chromosome • Transposons • Larger than Insertion sequences • Provide information for protein synthesis

  22. Sections A & B repeating but reversed “palindrome”

  23. Ames Test

  24. C. Bacterial Recombination

  25. Transformation Description Griffith's experiments Modern interpretation: Avery,McLeod & McCarty Mechanism Competence

  26. Conjugation • Male and female cells • Role of F factors (plasmids) • High frequency of recombination strains • Mechanism of Hfr conjugation • Sexduction

  27. Simple Conjugation

  28. Hfr Conjugation

  29. Transduction • Description • Role of the bacteriophage • The lytic cycle • Lysogeny • Generalized transduction

  30. Lysogeny

  31. F. Control of protein synthesis

  32. 1. Mechanism proposed by Jacob and Monod • 2. The operon theory • 3. Repressor-inductor model

  33. D. Genetic Engineering

  34. Genetic Engineering • Genetic Engineering Was Born from Genetic Recombination • Genetic engineering involves changing the genetic material in an organism to alter its traits or products • A recombinant DNA molecule contains DNA fragments spliced together from 2 or more organisms

  35. History of Genetic Engineering Discovery of endonucleases Plasmids and sticky ends

  36. Modern applications • Pharmaceutical production • Insulin, interferon, hormones, vaccines etc. • Genetically engineered plants • Animal gene alterations • Gene probes • DNA fingerprinting • The human genome initiative

  37. E. Genomics

  38. Microbial Genomes Have Been Sequenced • Hundreds of microbial genomes have been sequenced since the first in 1995 • Many of which are pathogens • Segments of the Human Genome May Have “Microbial Ancestors” • As many as 200 of the 35,000 human genes are essentially identical to those of Bacteria • They were passed down from early ancestors of humans

  39. Microbial Genomics Will Advance Our Understanding of the Microbial World • Knowing genomes of bacteria that cause food-borne diseases can help us: • develop detection methods • make food safer • It can help us identify microbes that cannot be cultured in the lab • Environmental genomics helps us understand how microbial communities function