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Microbial Models: The Genetics of Bacteria and Viruses Chapter 18 Figure 1. Typical mosaic pattern on flue-cured tobacco leaves infected with Tobacco mosaic virus. (Courtesy H.D. Shew) LE 18-2 Virus Bacterium Animal cell Animal cell nucleus 0.25 µm LE 18-4 Capsomere of capsid Membranous envelope Capsid RNA Capsomere DNA Glycoprotein 18 250 mm 20 nm Tobacco mosaic virus RNA Head Tail sheath Tail fiber DNA Glycoprotein 70–90 nm (diameter) 80–200 nm (diameter) 50 nm Adenoviruses 50 nm Influenza viruses 80 225 nm 50 nm Bacteriophage T4 LE 18-5 Entry into cell and uncoating of DNA VIRUS DNA Capsid 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 LE 18-6 Lytic Cycle Attachment Phage assembly Head Tails Release Entry of phage DNA and degradation of host DNA Tail fibers Assembly Synthesis of viral genomes and proteins Activity: Lytic Cycle LE 18-7 Phage DNA The phage attaches to a host cell and injects its DNA. Daughter cell with prophage Many cell divisions produce a large population of bacteria infected with the prophage. Phage DNA circularizes Phage Bacterial chromosome Lytic cycle The cell lyses, releasing phages. Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Lysogenic cycle Certain factors determine whether Lytic cycle or Lysogenic cycle is induced is entered New phage DNA and proteins are synthesized and assembled into phages. The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells. Prophage Phage DNA integrates into the bacterial chromosomes, becoming a prophage. Activity: Lytic & Lysogenic Cycle Class/Family Envelope Examples/Disease I. Double-stranded DNA (dsDNA) Adenovirus No Papovavirus No Herpesvirus Yes Poxvirus Yes Respiratory diseases, animal tumors Papillomavirus (warts, cervical cancer): polyomavirus (animal tumors) Herpes simplex I and II (cold sores, genital sores); varicella zoster (shingles, chicken pox); Epstein-Barr virus (mononucleosis, Burkitt’s lymphoma) Smallpox virus, cowpox virus Class/Family Envelope Examples/Disease II. Single-stranded DNA (ssDNA) Parvovirus No B19 parvovirus (mild rash) III. Double-stranded RNA (dsRNA) Reovirus No Rotavirus (diarrhea), Colorado tick fever virus Class/Family Envelope Examples/Disease IV. Single-stranded RNA (ssRNA); serves as mRNA Picornavirus No Rhinovirus (common cold); poliovirus, hepatitis A virus, and other enteric (intestinal) viruses Coronavirus Yes Severe acute respiratory syndrome (SARS) Flavivirus Yes Yellow fever virus, West Nile virus, hepatitis C virus Togavirus Yes Rubella virus, equine encephalitis viruses Class/Family Envelope Examples/Disease V. ssRNA; template for mRNA synthesis Filovirus Yes Orthomyxovir Yes us Paramyxoviru Yes s Rhabdovirus Yes Ebola virus (hemorrhagic fever) Influenza virus Measles virus; mumps virus Rabies virus VI. ssRNA; template for DNA synthesis Retrovirus Yes HIV (AIDS); RNA tumor viruses (leukemia) Figure 18.9 Viral infection of plants Figure 18-12 LE 18-13 PRIONS = infectious proteins which cause degenerative brain diseases (like mad cow disease); most likely transmitted in food Prion Original prion Many prions Normal protein New prion LE 18-14 Replication fork Origin of replication Termination of replication Figure 18.x7 E. coli Figure 18.x8 E. coli dividing Figure 18.x10 Plasmids Figure 18.12 Detecting genetic recombination in bacteria Figure 18.13 Transduction (Layer 4) LE 18-17 Sex pilus 5 µm Figure 18.15 Conjugation and recombination in E. coli (Layer 4) Figure 18.16 Insertion sequences, the simplest transposons Figure 18.17 Insertion of a transposon and creation of direct repeats LE 18-19 Insertion sequence 5 3 3 5 Inverted repeat Transposase gene Inverted repeat Transposon Insertion sequence Antibiotic resistance gene Insertion sequence 5 3 3 5 Inverted repeat Transposase gene Figure 18.18 Anatomy of a composite transposon LE 18-20 Regulation of enzyme activity Precursor Regulation of enzyme production Feedback inhibition Enzyme 1 Gene 1 Enzyme 2 Gene 2 Regulation of gene expression Enzyme 3 Gene 3 Enzyme 4 Gene 4 Enzyme 5 Tryptophan Gene 5 LE 18-21a trp operon Promoter Promoter Genes of operon DNA Regulatory gene mRNA trpE trpR 3 trpC trpB trpA C B A Operator Start codon Stop codon RNA polymerase mRNA 5 5 E Protein trpD Inactive repressor D Polypeptides that make up enzymes for tryptophan synthesis Tryptophan absent, repressor inactive, operon on LE 18-21b_1 DNA mRNA Active repressor Protein Tryptophan (corepressor) Tryptophan present, repressor active, operon off LE 18-21b_2 DNA No RNA made mRNA Active repressor Protein Tryptophan (corepressor) Tryptophan present, repressor active, operon off LE 18-22a Promoter Regulatory gene Operator lacl DNA lacZ No RNA made 3 mRNA 5 Protein RNA polymerase Active repressor Lactose absent, repressor active, operon off LE 18-22b lac operon DNA lacZ lacl 3 mRNA 5 lacA Permease Transacetylase RNA polymerase mRNA 5 -Galactosidase Protein Allolactose (inducer) lacY Inactive repressor Lactose present, repressor inactive, operon on Activity: lac Operon LE 18-23 Promoter DNA lacl lacZ CAP-binding site Active CAP cAMP RNA Operator polymerase can bind and transcribe Inactive lac repressor Inactive CAP Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized Promoter DNA lacl CAP-binding site Inactive CAP lacZ Operator RNA polymerase can’t bind Inactive lac repressor Lactose present, glucose present (cAMP level low): little lac mRNA synthesized Figure 18.x6 Herpes Figure 18.x1 Smallpox Figure 18.x3 Polio LE 18-8 Capsid Capsid and viral genome enter cell RNA HOST CELL Envelope (with glycoproteins) Viral genome (RNA) Template mRNA ER Glycoproteins Capsid proteins Copy of genome (RNA) New virus LE 18-11 Young ballet students in Hong Kong wear face masks to protect themselves from the virus causing SARS. 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. Figure 18.x4 Hepatitis Figure 18.x5 Influenza epidemic Figure 18.x2 Measles LE 18-9 Glycoprotein Viral envelope Capsid Reverse transcriptase RNA (two identical strands) LE 18-10 HIV Membrane of white blood cell HOST CELL Reverse transcription Viral RNA 0.25 µm HIV entering a cell RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation New HIV leaving a cell mRNA Activity: HIV Reproductive Cycle Figure 18.7x1 HIV infection
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