Microbial Models: The Genetics of Bacteria and Viruses

1. Microbial Models: The Genetics of Bacteria and Viruses Chapter 18

2. Figure 1.  Typical mosaic pattern on flue-cured tobacco leaves infected with Tobacco mosaic virus. (Courtesy H.D. Shew)

3. Virus LE 18-2 Bacterium Animal cell Animal cell nucleus 0.25 µm

4. Capsomere of capsid Membranous envelope RNA Capsomere Capsid LE 18-4 DNA Head RNA DNA Tail sheath Tail fiber Glycoprotein Glycoprotein 70–90 nm (diameter) 80–200 nm (diameter) 18  250 mm 80  225 nm 20 nm 50 nm 50 nm 50 nm Tobacco mosaic virus Adenoviruses Influenza viruses Bacteriophage T4

5. VIRUS Entry into cell and uncoating of DNA DNA Capsid LE 18-5 Transcription Replication HOST CELL Viral DNA mRNA Viral DNA Capsid proteins Self-assembly of new virus particles and their exit from cell Activity: Viral Reproductive Cycle

7. Lytic Cycle Attachment LE 18-6 Entry of phage DNA and degradation of host DNA Phage assembly Release Head Tail fibers Tails Synthesis of viral genomes and proteins Assembly Activity: Lytic Cycle

8. Phage DNA The phage attaches to a host cell and injects its DNA. Daughter cell with prophage LE 18-7 Many cell divisions produce a large population of bacteria infected with the prophage. Phage DNA circularizes Phage Bacterial chromosome Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Lytic cycle Lysogenic cycle The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells. Certain factors determine whether The cell lyses, releasing phages. Lytic cycle is induced Lysogenic cycle is entered or Prophage Phage DNA integrates into the bacterial chromosomes, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages. Activity: Lytic & Lysogenic Cycle

13. Figure 18.9 Viral infection of plants

14. Figure 18-12

15. PRIONS = infectious proteins which cause degenerative brain diseases (like mad cow disease); most likely transmitted in food LE 18-13 Original prion Prion Many prions New prion Normal protein

17. Replication fork LE 18-14 Origin of replication Termination of replication

18. Figure 18.x7 E. coli

19. Figure 18.x8 E. coli dividing

20. Figure 18.x10 Plasmids

21. Figure 18.12 Detecting genetic recombination in bacteria

23. Figure 18.13 Transduction (Layer 4)

24. LE 18-17 Sex pilus 5 µm

25. Figure 18.15 Conjugation and recombination in E. coli (Layer 4)

26. Figure 18.16 Insertion sequences, the simplest transposons

27. Figure 18.17 Insertion of a transposon and creation of direct repeats

28. Insertion sequence LE 18-19 5¢ 3¢ 3¢ 5¢ Inverted repeat Inverted repeat Transposase gene Transposon Insertion sequence Insertion sequence Antibiotic resistance gene 5¢ 3¢ 3¢ 5¢ Transposase gene Inverted repeat

29. Figure 18.18 Anatomy of a composite transposon

30. Regulation of enzyme production Regulation of enzyme activity Precursor Feedback inhibition LE 18-20 Enzyme 1 Gene 1 Gene 2 Enzyme 2 Regulation of gene expression Gene 3 Enzyme 3 Enzyme 4 Gene 4 Gene 5 Enzyme 5 Tryptophan

31. LE 18-21a trp operon Promoter Promoter Genes of operon DNA trpB trpA trpE trpC trpD trpR Operator Stop codon RNA polymerase Regulatory gene Start codon 3¢ mRNA 5¢ mRNA 5¢ D B E C A Inactive repressor Protein Polypeptides that make up enzymes for tryptophan synthesis Tryptophan absent, repressor inactive, operon on

32. DNA LE 18-21b_1 mRNA Active repressor Protein Tryptophan (corepressor) Tryptophan present, repressor active, operon off

33. DNA LE 18-21b_2 No RNA made mRNA Active repressor Protein Tryptophan (corepressor) Tryptophan present, repressor active, operon off

34. Promoter Regulatory gene LE 18-22a Operator lacl lacZ DNA No RNA made 3¢ mRNA RNA polymerase 5¢ Active repressor Protein Lactose absent, repressor active, operon off

35. LE 18-22b lac operon DNA lacl lacY lacA lacZ RNA polymerase 3¢ mRNA mRNA 5¢ 5¢ Transacetylase Permease -Galactosidase Protein Inactive repressor Allolactose (inducer) Lactose present, repressor inactive, operon on Activity: lac Operon

36. Promoter DNA lacl lacZ LE 18-23 RNA polymerase can bind and transcribe Operator CAP-binding site Active CAP cAMP Inactive lac repressor Inactive CAP Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized Promoter DNA lacl lacZ Operator CAP-binding site RNA polymerase can’t bind Inactive CAP Inactive lac repressor Lactose present, glucose present (cAMP level low): little lac mRNA synthesized

38. Figure 18.x6 Herpes

39. Figure 18.x1 Smallpox

40. Figure 18.x3 Polio

41. Capsid Capsid and viral genome enter cell RNA LE 18-8 HOST CELL Envelope (with glycoproteins) Viral genome (RNA) Template mRNA Capsid proteins ER Glyco- proteins Copy of genome (RNA) New virus

42. LE 18-11 The SARS-causing agent is a coronarvirus like this one (colorized TEM), so named for the “corona” of glyco-protein spikes protruding form the envelope. Young ballet students in Hong Kong wear face masks to protect themselves from the virus causing SARS.

43. Figure 18.x4 Hepatitis

44. Figure 18.x5 Influenza epidemic

45. Figure 18.x2 Measles

46. Viral envelope Glycoprotein LE 18-9 Capsid RNA (two identical strands) Reverse transcriptase

47. Membrane of white blood cell HIV LE 18-10 HOST CELL Reverse transcription Viral RNA RNA-DNA hybrid 0.25 µm HIV entering a cell DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation mRNA Activity: HIV Reproductive Cycle New HIV leaving a cell

48. Figure 18.7x1 HIV infection