Prokaryotes and Viruses Adapted from presentation by Stephanie Bolton, White County High School, Georgia

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 Figure 21.3 Page 348 DNA capsule plasma membrane ribosomes in cytoplasm bacterial flagellum pilus cell wall 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 Bacterium before bacterial chromosome DNA replication bacterial chromosome DNA replication begins Figure 21.7 Page 350

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

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

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

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

Eubacteria cont.

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/decomposers 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) Helical virus 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 Fig. 21.18 Page 356 viral coat (proteins)

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

Lysis of host cell is induced; infectious particles escape. Lytic Pathway 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

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

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 Animal 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 Drug-resistant strains Food poisoning Ebola virus Monkeypox virus Drug-resistant strains Food poisoning E. coli Salmonella