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Prokaryotes, Viruses, and Protistans Chapter 20. Microorganisms Single-celled organisms that are too small to be seen without a microscope Bacteria are.

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Presentation on theme: "Prokaryotes, Viruses, and Protistans Chapter 20. Microorganisms Single-celled organisms that are too small to be seen without a microscope Bacteria are."— Presentation transcript:

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

6 Bacterial Shapes coccusbacillus 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

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) Polyhedral virusHelical 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 Virus injects genetic material Production of viral components Assembly Lysis Assembly

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

18 Replication of an Enveloped Virus DNA replication Transcription of viral genes Translation 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 –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 merozoite Male and female gametocytes in blood sporozites Gametes form in mosquito gut, combine to form zygotes Offspring enter blood, cause malarial symptoms


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