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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 • Arose before the eukaryotes Prokaryotic Characteristics • No membrane-bound nucleus • Single chromosome • Cell wall (in most species) • Prokaryotic fission • Metabolic diversity Prokaryotic Body Plan DNA capsule bacterial flagellum Figure 21.3 Page 348 pilus plasma membrane cell wall ribosomes in cytoplasm cytoplasm Bacterial Shapes coccus bacillus spirillum In-text figure Page 348 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 Prokaryotic Fission - 1 bacterial chromosome Bacterium before DNA replication DNA replication begins Figure 21.7 Page 350 Prokaryotic Fission - 2 parent DNA molecule DNA replication completed DNA copy Membrane growth moves DNA molecules apart Figure 21.7 Page 350 Prokaryotic Fission - 3 New membrane and cell-wall material deposited Cytoplasm divided in two Figure 21.7 Page 350 nicked plasmid in donor cell Conjugation Transfer of plasmid Figure 21.8 Page 351 conjugation tube to recipient cell Prokaryotic Classification EUBACTERIA (Bacteria) ARCHAEBACTERIA (Archaea) EUKARYOTES (Eukarya) •Traditionally classified by numerical taxonomy •Now increased use of comparative biochemistry Figure 21.9 Page 351 Archaebacteria Methanogens-live in oxygen free habitats (form methane gas as a biproduct) Extreme halophiles- can survive in extreme salt Extreme thermophiles- can survive extreme heat WHERE MIGHT WE FIND THESE TODAY? Eubacteria • Includes most familiar bacteria • Most have cell wall; always includes peptidoglycan • Classification based largely on metabolism Metabolic Diversity • Photoautotrophs- use light & inorganic carbon dioxide to make organic compounds. (like plants) • Photoheterotrophs- use light & obtain carbon from ORGANIC sources. (halophiles) • Chemoautotrophs- Use chemicals as energy source + inorganic carbon dioxide. • Chemoheterotrophs-must consume organic compounds to get energy & carbon. (Most common) Some Pathogenic Eubacteria • Most are chemoheterotrophs/decomp osers – E. coli strains – Clostridium botulinum – Clostridium tetanus – Borrelia burgdorferi – Rickettsia rickettsii 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 Virus • Noncellular infectious agent • Protein wrapped around a nucleic acid core • Cannot reproduce itself; can only be reproduced using a host cell Viral Body Plans Complex virus (bacteriophage) • Genetic material is DNA or RNA (not both) • Coat is protein Helical virus Polyhedral virus Fig. 21.18 Page 356 Enveloped Virus (HIV) viral protein lipid envelope (derived from host) viral RNA reverse transcriptase viral coat (proteins) Fig. 21.18 Page 356 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 Lytic Pathway 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. Stepped Art Fig. 21.20 Page 358 Lysogenic Pathway Viral DNA usually becomes integrated into the bacterial chromosome. Prior to prokaryotic fission, the chromosome and integrated viral DNA are replicated. Viral DNA is excised from chromosome and cell enters lytic pathway. After binary fission, each daughter cell will have recombinant DNA. Stepped Art Fig 21.20 (2) Page 358 Replication of an Enveloped Virus DNA virus particle plasma membrane of host cell Replication of viral DNA Transcription of viral DNA Translation viral DNA some proteins for viral coat nuclear envelope other proteins for viral envelope Figure 21.21 Page 359 Viroids • Smaller than viruses • Strands or circles of RNA • No protein-coding genes • No protein coat • Cause many plant diseases Prions • Small proteins • Linked to human diseases – Kuru – Creutzfeldt-Jakob disease (CJD) • Animal diseases – Scrapie in sheep – Bovine spongiform encephalopathy (mad cow disease) Nature of Disease • Contagious disease pathogens must directly contact a new host • Epidemic • Pandemic (AIDS) • Sporadic • Endemic 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 New Threats • Emerging Pathogens – Ebola virus – Monkeypox virus • Drug-resistant strains • Food poisoning – E. coli – Salmonella Reading Assignment- Due by end of year! • Read THE HOT ZONE by Richard Preston • Write a summary/evaluation of the book. • It is all true, & it will scare you to death!!