1. Prokaryotes, Viruses, and Protistans
Chapter 20

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 pilus DNA bacterial flagellum
ribosomes in cytoplasm
plasma membrane
capsule
cell wall

6. Bacterial Shapes
coccus
bacillus
spirillum

7. Archaebacteria
Methanogens
Extreme halophiles
Extreme thermophiles

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

9. 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

10. Prokaryotic Fission

11. Conjugation nicked plasmid in donor cell conjugation tube
to recipient cell
Conjugation

12. Virus Noncellular infectious agent
Consists of protein wrapped around a nucleic acid core
Cannot reproduce itself; can only be reproduced using a host cell

13. Viral Body Plans Genetic material is DNA or RNA Coat is protein
Complex virus
(bacteriophage)
Helical virus
Polyhedral virus

14. Enveloped Virus (HIV)
lipid envelope; proteins span the envelope, line its inner surface, spike out above it
viral coat
(proteins)

15. Viral Multiplication - Basic Steps
Virus attaches to host cell
Whole virus or genetic material enters host
Viral DNA or RNA directs host to make viral genetic material and protein
Viral nucleic acids and proteins are assembled
New viral particles are released from cell

16. Lytic Pathway Lysis Assembly Assembly Virus injects genetic material
Production of
viral components

17. Lysogenic Pathway Latent period extends the cycle
Stimulus may cause cell
to enter lytic pathway
Latent period extends the cycle
Viral DNA becomes part of host chromosome for a time
Viral material
passed on
Viral material
integrated

18. Replication of an Enveloped Virus
Transcription
of viral genes
Translation
DNA replication
Proteins
Assembly

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

20. 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)

21. Protistans Differ from Prokaryotes
Have a nucleus and organelles
Have proteins associated with DNA
Use microtubules in a cytoskeleton, spindle apparatus, and cilia and flagella
May contain chloroplasts
May divide by mitosis and meiosis

22. Sporozoans
Parasitic
Complete part of the life cycle inside specific cells of a host organism
Many have elaborate life cycles that require different hosts
Many cause serious human disease

23. Cryptosporidium (Giardia)
Motile infective stage (sporozoite) invades intestinal epithelium
Causes cramps, watery diarrhea
Commonly transmitted by water contaminated with cysts

24. Toxoplasma Cysts may be ingested with raw or undercooked meat
Exposure to cysts from cat feces
Symptoms are usually mild in people with normal immune function
Infection during pregnancy can kill or damage the embryo

25. Malaria Symptoms have been known for more than 2,000 years
Most prevalent in tropical and subtropical parts of Africa
Kills a million Africans each year
Caused by four species of Plasmodium
Transmitted by Anopheles mosquitoes

26. Plasmodium Life Cycle sporozites sporozites Gametes form
in mosquito gut,
combine to form
zygotes
merozoite
Offspring enter blood, cause malarial symptoms
Male and female
gametocytes
in blood