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Prokaryotes and Viruses

Prokaryotes and Viruses. Chapter 21. Microorganisms. Single-celled organisms that are too small to be seen without a microscope Bacteria are the smallest living organisms Viruses are smaller but are not alive. The Prokaryotes. Only two groups Archaebacteria and Eubacteria

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Prokaryotes and Viruses

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  1. Prokaryotes and Viruses Chapter 21

  2. Microorganisms • Single-celled organisms that are too small to be seen without a microscope • Bacteria are the smallest living organisms • Viruses are smaller but are not alive

  3. The Prokaryotes • Only two groups • Archaebacteria and Eubacteria • Arose before the eukaryotes

  4. Prokaryotic Characteristics • No membrane-bound nucleus • Single chromosome • Cell wall (in most species) • Prokaryotic fission • Metabolic diversity

  5. Prokaryotic Body Plan DNA capsule plasma membrane ribosomes in cytoplasm bacterial flagellum Figure 21.3Page 348 pilus cell wall cytoplasm

  6. Bacterial Shapes coccus bacillus spirillum In-text figurePage 348

  7. Metabolic Diversity • Photoautotrophs • Chemoautotrophs • Chemoheterotrophs

  8. Bacterial Genes • Bacteria have a single chromosome • Circular molecule of DNA • Many bacteria also have plasmids • Self-replicating circle of DNA that has a few genes • Can be passed from one cell to another

  9. DNA replication begins Prokaryotic Fission - 1 Bacterium before DNA replication bacterial chromosome Figure 21.7 Page 350

  10. Membrane growth moves DNA molecules apart DNA replication completed parent DNA molecule DNA copy Prokaryotic Fission - 2 Figure 21.7 Page 350

  11. New membrane and cell-wall material deposited Cytoplasm divided in two Prokaryotic Fission - 3 Figure 21.7 Page 350

  12. nicked plasmid in donor cell conjugation tube to recipient cell Conjugation Transfer of plasmid Figure 21.8Page 351

  13. EUBACTERIA (Bacteria) ARCHAEBACTERIA (Archaea) EUKARYOTES (Eukarya) Prokaryotic Classification • Traditionally classified by numerical taxonomy • Now increased use of comparative biochemistry Figure 21.9Page 351

  14. Archaebacteria Methanogens Extreme halophiles Extreme thermophiles

  15. Eubacteria • Includes most familiar bacteria • Have fatty acids in plasma membrane • Most have cell wall; always includes peptidoglycan • Classification based largely on metabolism

  16. Eubacterial Diversity • Photoautotrophic • Aerobic (Cyanobacteria) • Anaerobic (Green bacteria) • Chemoautotrophic • Important in nitrogen cycle • Chemoheterotrophic • Largest group

  17. Some Pathogenic Eubacteria • Most are chemoheterotrophs • E. coli strains • Clostridium botulinum • Clostridium tetanus • Borrelia burgdorferi • Rickettsiarickettsii

  18. Bacterial Behavior • Bacteria move toward nutrient-rich regions • Aerobes move toward oxygen; anaerobes avoid it • Photosynthetic types move toward light • Magnetotactic bacteria swim downward • Myobacteria show collective behavior

  19. Virus • Noncellular infectious agent • Protein wrapped around a nucleic acid core • Cannot reproduce itself; can only be reproduced using a host cell

  20. Viral Body Plans Complex virus (bacteriophage) • Genetic material is DNA or RNA • Coat is protein Helical virus Polyhedral virus Fig. 21.18Page 356

  21. Enveloped Virus (HIV) viral protein lipid envelope (derived from host) viral RNA reverse transcriptase Fig. 21.18Page 356 viral coat (proteins)

  22. Viral Multiplication - Basic Steps • Attach to host cell • Enter host (virus or just genetic material) • Direct host to make viral genetic material and protein • Assemble viral nucleic acids and proteins • Release new viral particles

  23. Lysis of host cell is induced; 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 machinery to produce viral proteins and viral DNA. Lytic Pathway Stepped ArtFig. 21.20 Page 358

  24. Viral DNA is excised from chromosome and cell enters lytic pathway. Viral DNA usually becomes integrated into the bacterial chromosome. After binary fission, each daughter cell will have recombinant DNA. Prior to prokaryotic fission, the chromosome and integrated viral DNA are replicated. Lysogenic Pathway Stepped ArtFig 21.20 (2)Page 358

  25. DNA virus particle Replication of anEnvelopedVirus plasma membrane of host cell Transcription of viral DNA Replication of viral DNA Translation nuclear envelope some proteins for viral coat viral DNA other proteins for viral envelope Figure 21.21Page 359

  26. Viroids • Smaller than viruses • Strands or circles of RNA • No protein-coding genes • No protein coat • Cause many plant diseases

  27. Prions • Small proteins • Linked to human diseases • Kuru • Creutzfeldt-Jakob disease (CJD) • Animal diseases • Scrapie in sheep • Bovine spongiform encephalopathy (mad cow disease)

  28. Nature of Disease • Contagious disease pathogens must directly contact a new host • Epidemic • Pandemic (AIDS) • Sporadic • Endemic

  29. 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

  30. New Threats • Emerging Pathogens • Ebola virus • Monkeypox virus • Drug-resistant strains • Food poisoning • E. coli • Salmonella

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