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  1. 1. VIRUSES Non-cellular infectious agents (Chapter 10, sections 17-21) VIRUSES • Two major characteristics 65–nm diameter head, DNA 225 nm total length protein coat sheath base tail plate fiber Fig. 21-13c, p.342 1
  2. 2. viral RNA protein subunits of coat 80 nm diameter 80 nm diameter 18 nm diameter, 250 nm length viral coat (proteins) reverse transcriptase 100-120 nm diameter viral RNA lipid envelope: proteins span the envelope, line its inner surface, spike out above it Fig. 21-13d, p.342 VIRUSES • Examples 2
  3. 3. Bacteriophage Fig. 21-15a, p.344 HIV SARS virus Ebola virus VIRUSES How they multiply 3
  4. 4. Lysis of host cell is induced; Lytic Pathway infectious particles escape. Tail fibers and other parts are added to coats. Virus particles bind to wall of suitable host. Viral genetic material enters cell cytoplasm. Viral protein molecules are assembled into coats; DNA is packaged inside. Viral DNA directs host Stepped Art machinery to produce viral proteins and viral DNA. Fig. 21-15b, p.344 Lysogenic Pathway Viral DNA is excised from chromosome and cell Viral DNA usually becomes enters lytic pathway. integrated into the bacterial chromosome. After binary fission, each Prior to prokaryotic fission, the daughter cell will have chromosome and integrated recombinant DNA. Stepped Art viral DNA are replicated. Fig. 21-15c, p.344 e Lysis of host cell is induced; infectious particles escape. d The coats get tail fibers, other parts. Lytic Pathway a Virus particle injects genetic c Viral proteins are assembled material into a suitable host cell into coats around viral DNA. after binding to its wall. b Viral DNA directs host cell to make viral proteins and replicate viral DNA. a-1 Viral DNA is integrated a-4 Viral DNA is excised into the host’s chromosome. from the chromosome. Lysogenic Pathway a-2 Before prokaryotic fission, the a-3 After cell division, each daughter bacterial chromosome with the cell will have recombinant DNA. integrated viral DNA is replicated. Fig. 21-15, p.344 4
  5. 5. animation Fig. 21-16, p.345 Infectious Diseases and Evolution 5
  6. 6. Evolution and Disease • Host and pathogen are coevolving • If a pathogen kills too quickly, it might disappear along with the individual host • Most dangerous if pathogen – Is overwhelming in numbers – Is in a novel host – Is a mutant strain Mycobacterium tuberculosis SARS virus Ebola virus 6
  7. 7. New Threats • Emerging Pathogens – Ebola virus – Monkeypox virus – SARS virus • Drug-resistant strains • Food poisoning – E. coli – Salmonella 7
  8. 8. Salmonella attached to a knife blade Fig. 21-18b p.349 8