1 / 45

Viral & Prokaryotic Genetics

Viral & Prokaryotic Genetics. “Simple” Model Systems. Experimental Model Systems for Genetics. characteristics of good model systems small genome size E. coli : ~4 million base pairs (bp) l bacteriophage: ~45,000 bp large population size E. coli : ~one billion (10 9 ) per liter

pearlie
Download Presentation

Viral & Prokaryotic Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Viral & Prokaryotic Genetics “Simple” Model Systems

  2. Experimental Model Systems for Genetics • characteristics of good model systems • small genome size • E. coli: ~4 million base pairs (bp) • l bacteriophage: ~45,000 bp • large population size • E. coli: ~one billion (109) per liter • l bacteriophage: ~100 billion (1011) per liter

  3. Experimental Model Systems for Genetics • characteristics of good model systems • short generation time • E. coli:18-20 minutes • O/N: 45 generations [1 => 1.76 x 1013] • l bacteriophage: ~20 minutes • haploid genome • genotype => phenotype

  4. viruses are smallTable 13.1

  5. Viruses • small • resistant to inactivation by • alcohol • dehydration • infectivity may decrease; can’t increase • reproduction: obligate intracellular parasites • uses host nucleotides, amino acids, enzymes • hosts • animals, plants, fungi, protists, prokaryotes

  6. Viruses • virus structure • virion = virus particle • central core = genome: DNA or RNA • capsid = protein coat; determines shape • lipid/protein membrane on some animal viruses

  7. Viruses • virus classification • host kingdom • genome type (DNA or RNA) • strandedness (single or double) • virion shape • capsid symmetry • capsid size • +/- membrane

  8. Viruses • bacteriophage (“bacteria eater”) • reproduction • lytic cycle: virulent phages • infection, growth, lysis • lysogenic cycle: temperate phages • infection, incorporation, maintenance

  9. bacteriophage l life cyclesFigure 13.2

  10. Viruses • expression of bacteriophage genes during lytic infection • early genes - immediate • middle genes • depends on early genes • replicates viral DNA • late genes • packages DNA • prepares for lysis

  11. bacteriophage lytic life cycleFigure 13.3

  12. mammalian influenza virusFigure 13.4

  13. HIV retrovirus structureFigure 13.5

  14. Laboratory Propagation of BacteriaFigure 13.6

  15. Prokaryotes • bacteria reproduce by binary fission • reproduction produces clones of identical cells • research requires growth of pure cultures • auxotrophic bacteria with different requirements can undergo recombination

  16. bacteria exhibit genetic recombinationFigure 13.7 minimal minimal + Met, Biotin complete minimal + Met, Biotin, Thr, Leu minimal minimal minimal + Thr, Leu

  17. genetic recombination in bacteriaFigure 13.9

  18. transformation: scavenging DNAFigure 13.10

  19. transduction: viral transferFigure 13.10 generalized transduction specialized transduction

  20. Prokaryotes • recombination exchanges new DNA with existing DNA • three mechanisms can provide new DNA • transformation - takes up DNA from the environment • transduction - viral transfer from one cell to another • conjugation - genetically programmed transfer from donor cell to recipient cell

  21. conjugation: programmed genetic exchange programmed by the chromosome or by an F (fertility) plasmid Figure 13.11

  22. Prokaryotes • Plasmids provide additional genes • small circular DNAs with their own ORIs • most carry a few genes that aid their hosts • metabolic factors carry genes for unusual biochemical functions • F factors carry genes for conjugation • Resistance (R) factors carry genes that inactivate antibiotics and genes for their own transfer

  23. of a geneFigure 13.12 transpositional inactivation

  24. Transposable Elements • mobile genetic elements • move from one location to another on a DNA molecule • may move into a gene - inactivating it • may move chromosome => plasmid => new cell => chromosome • may transfer an antibiotic resistance gene from one cell to another

  25. of a gene transpositional inactivation an additional gene hitchhiking on a Transposon Figure 13.12

  26. Regulation of Gene Expression • transcriptional regulation of gene expression • saves energy • constitutive genes are always expressed • regulated genes are expressed only when they are needed

  27. alternate regulatory mechanismsFigure 13.14

  28. Regulation of Gene Expression • transcriptional regulation of gene expression • the E. colilac operon is inducible

  29. enzyme induction in bacteria Figure 13.13

  30. the lac operon of E. coliFigure 13.16

  31. Regulation of Gene Expression • regulation of lac operon expression • the lac operon encodes catabolic enzymes • the substrate (lactose) comes and goes • the cell does not need a catabolic pathway if there is no substrate • the lac operon is inducible • expressed only when lactose is present • allolactose is the inducer

  32. a repressor protein blocks transcriptionlac repressor blocks transcription Figures 13.15, 13.17 promoter gene

  33. Regulation of Gene Expression • regulation of lac operon expression • lac repressor (lac I gene product) blocks transcription • lac inducer inactivates lac repressor

  34. lac inducer inactivates the lac repressorFigure 13.17

  35. trp repressor is normally inactive; trp operon is transcribedFigure 13.18

  36. Regulation of Gene Expression • regulation of trp operon expression • the trp operon encodes anabolic enzymes • the product is normally needed • the cell needs an anabolic pathway except when the amount of product is adequate • the trp operon is repressible • trp repressor is normally inactive • trp co-repressor activates trp repressor when the amount of tryptophan is adequate

  37. trp co-repressor activates trp repressor; trp operon is not transcribedFigure 13.18

  38. positive and negative regulation • both lac and trp operons are negativelyregulated • each is regulated by a repressor • lac operon is also positively regulated • after lac repressor is inactivated by the inducer, transcription must be stimulated by a positive regulator

  39. inducedlac operon alsorequiresactivation before genesare transcribedinducedlac operon alsorequiresactivation before genesare transcribed Figure 13.19

  40. positive & negative regulation ofthe lac operonTable 13.2

  41. positive and negative regulation in  bacteriophage • the “decision” between lysis & lysogeny depends on a competition between two repressors

  42. lysis vs. lysogenyFigure 13.20 in a healthy, well-nourished culture in a slow-growing nutrient-poor culture

  43. map of the entire Haemophilus influenzae chromosomeFigure 13.21

  44. new tools for discovery • genome sequencing reveals previously unknown details about prokaryotic metabolism • functional genomics identifies the genes without a known function • comparative genomics reveals new information by finding similarities and differences among sequenced genomes

  45. How many genes does it take…?Figure 13.22

More Related