What are Viruses? How Can Viral Diseases be Controlled?

• Viruses– Non-living, but evolve quickly (small genomes); much smaller than

bacteria cells (20 – 250 nm)– Not identified until 1935; some still difficult to keep in culture– Protein capsid surrounds DNA or RNA core (some with envelope)– Common naturally; some emerging as evolve, or as host organisms

gain new exposure to humans (exs., “bird flu”, Ebola, SARS, H1N1)

– Bacteriophages infect and can destroy bacteria cells• Lytic and Lysogenic Cycles

• Control of Viral Diseases– Vaccinations stimulate the immune system via inoculation with an

inactivated strain (exs., polio, measles, mumps, rubella)• Original smallpox vaccine by Edward Jenner involved cowpox strain

– Anti-viral Drugs: interfere with viral reproduction (exs., acyclovir, AZT) – Prevention and Control: epidemiologists attempt to control spread of

disease by identifying (sometimes eliminating) host organisms; encouraging hygienic and behavioral mechanisms of control

Fig. 19-3RNA

Capsomere

Capsomereof capsid

DNA

Glycoprotein

18 250 nm 70–90 nm (diameter)

Glycoproteins

80–200 nm (diameter) 80 225 nm

Membranousenvelope RNA

Capsid

HeadDNA

Tailsheath

Tailfiber

50 nm50 nm50 nm20 nm

(a) Tobacco mosaic virus

(b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4

Fig. 19-6PhageDNA

Phage

The phage injects its DNA.

Bacterialchromosome

Phage DNAcircularizes.

Daughter cellwith prophage

Occasionally, a prophageexits the bacterialchromosome,initiating a lytic cycle.

Cell divisionsproducepopulation ofbacteria infectedwith the prophage.

The cell lyses, releasing phages.

Lytic cycle

Lytic cycleis induced or Lysogenic cycle

is entered

Lysogenic cycle

Prophage

The bacterium reproduces,copying the prophage andtransmitting it to daughter cells.

Phage DNA integrates intothe bacterial chromosome,becoming a prophage.

New phage DNA and proteinsare synthesized andassembled into phages.

How are Living Things Categorized?• “Animal/Vegetable/Mineral” outdated (Aristotle)

– Some life on Earth neither plants nor animals (ex. Euglena: once inbotany texts as a plant with animal-like mobility, while in

zoology texts as a photosynthetic animal)

• Domain System (Archaea, Eubacteria, Eukarya)– Great genetic differences between the two groups of prokaryotes

• Six Kingdoms (major groups of living things)– Kingdom Archaea: single celled, small cells, prokaryotic, thermophilic

or methanogenic– Kingdom Monera (Eubacteria): single celled; small cells; prokaryotic – Kingdom Protista: single celled or colonies; eukaryotic– Kingdom Fungi: single celled or colonies; eukaryotic– Kingdom Plantae: multi-cellular; eukaryotic; photosynthetic– Kingdom Animalia: multi-cellular; eukaryotic; heterotrophic

Fig. 26-21

Fungi

EUKARYA

Trypanosomes

Green algaeLand plants

Red algae

ForamsCiliates

Dinoflagellates

Diatoms

Animals

AmoebasCellular slime molds

Leishmania

Euglena

Green nonsulfur bacteria

Thermophiles

Halophiles

Methanobacterium

Sulfolobus

ARCHAEA

COMMONANCESTOR

OF ALLLIFE

BACTERIA

(Plastids, includingchloroplasts)

Greensulfur bacteria

(Mitochondrion)

Cyanobacteria

ChlamydiaSpirochetes

Figures 26.22 and 26.23

What are the Different Types of Bacteria, and How Do They Impact Our Lives?

• Kingdom Archaebacteria– Prokaryotic, small cells; found in environments similar to “archaic Earth”– Diversity

• Methanogens: anaerobic; produce methane (“natural gas”); found in mudflats• Halophiles: “salt-loving”; found in hypersaline environments• Thermophiles: anaerobic; found in hot springs/undersea vents; use sulfur dioxide

as an energy source (chemosynthetic)

• Kingdom Eubacteria (Monera)– Prokaryotic, small cells, many form resistant (dormant) spores; omnipresent– Diversity

• Three main morphologies: cocci (spherical), bacillus (rods), spirochaetes (spiral); shape often first criterion for identification (stains used, e.g.,

Gram stain)• Cyanobacteria: photosynthetic; common in top 1mm of ocean; form chains and

colonies (stromatolite fossils from 2 bya)– Common pathogens: syphilis, anthrax, botulism, tuberculosis; evolving

increased resistance to antibiotics; many transfer genes via plasmids– Importance

• Symbiosis: vital for digestion in many mammals (E. coli and others in colon)• Decomposition and recycling of nutrients; nitrogen fixation and nitrification by

cyanobacteria at roots of plants (nitrogen gas usable forms); cyano- bacteria provide most of lower atmosphere’s oxygen

Figure 27.17

Figure 27.2

Figure 27.3

Figures 27.5, 27.6, and 27.12

Figures 27.14, 27.19 – 27.21

What are the Different Types of Plant-like Protists (Kingdom Protista), and How Do They Impact Our Lives?

• Algae (plant-like protists)– Eukaryotic, single cells or colonial (seaweeds

multicellular); photosynthetic (accessory pigments determine color/classification)

– Diversity and Importance

• Diatoms and Dinoflagellates: shells of silica or cellulose; abundant primary producers (phytoplankton); some cause red tides and shellfish poisoning (produce toxins and absorb pollutants)

• Euglenoids: photosynthetic and mobile with flagellum (ex. Euglena)

• Green Algae and Macroalgae (seaweeds): primary producers; extracts from kelp used as a thickener in many products; alternation of generations (gametophyte vs. sporophyte)

Figure 28.2

Figures 28.7, 28.9, and 28.13

Figure 28.3

Figures 28.15, 28.19a, and 28.21a

Figure28.16

What are the Different Types of Animal-like Protists (Kingdom Protista), and How Do They Impact Our Lives?

• Protozoans (animal-like protists)– Diversity and Importance (classified by

organelles of motility)• Ciliates: cilia; common primary consumers; reproduce

asexually by fission, sexually by conjugation

• Amoeboids: pseudopods; cause amoebic dysentery; shelled amoeboids are important zooplankton (foraminiferans and radiolarians)

• Zooflagellates: flagella; Trypanosoma brucei causes African sleeping sickness (tse tse fly vector)

• Sporozoans: non-motile; Plasmodium causes malaria (mosquito vectors); stages infect RBCs and liver

Figures 28.3, 28.6, 28.11a, and 28.18

Figure 28.10

Figure 28.25