1. Bacteria & Archaea and Viruses
Chapters 27 and 19

2. YOU MUST KNOW
The key ways in which prokaryotes differ from eukaryotes with respect to genome, membrane-bound organelles, size, and reproduction
How horizontal acquisition of genetic information occurs in prokaryotes via transformation, conjugation, and transduction
How these mechanisms plus mutation contribute to genetic diversity in prokaryotes
The components of a virus
The differences between lytic and lysogenic cycles
How viruses can introduce genetic variation into host organisms
Mechanisms that introduce genetic variation into viral populations

3. *Structurally different than eukaryotic flagella – analogous structures*

4. Reproduce by Binary Fission
Short reproduction times

5. Genetic Diversity
Transformation – a prokaryote takes up DNA from its environment
Transduction - Bacteriophage virus transfers genes from one prokaryote to another
Conjugation - Genes directly transferred from one prokaryote to another by a mating bridge formed by connected pili
Horizontal gene transfer = between different species
Mutations – rare, but main source
of genetic diversity in bacteria

6. Nutritional and Metabolic Adaptations
Obligate aerobes – require oxygen (use cellular respiration)
Obligate anaerobes – oxygen kills them, use fermentation
Facultative anaerobes – use oxygen if available, but can do fermentation
Nitrogen fixation - some prokaryotes can use atmospheric nitrogen directly – covert N2 to NH4+

7. Archaea
Many are extremophiles (live in extreme environments)
Extreme halophiles – saline environments (Great Salt Lake)
Extreme thermophiles – high temperatures (geyser pools)
Methanogens – use CO2 to oxidize H2 and produce methane – live in swamps, deep sea vents

8. Impact on Humans
Pathogens – produce poisons that kill infected organism
Antibiotics – kill prokaryotes but not viruses
Many bacterial plasmids contain genes for resistance
Bioremediation – removal of pollutants from soils, air, or water using prokaryotes
Symbionts – live in gut, produce vitamins and help digest food
Production of cheese, yogurt, etc

9. Smaller than ribosomes – about 20nm
Structure of a virus
Smaller than ribosomes – about 20nm
Composed of genetic material (double-stranded or single-stranded DNA or double-stranded or single-stranded RNA) surrounded by a capsid (protein shell)
Viral envelopes – membrane around the capsid that helps in invading hosts
Bacteriophage – virus that infects bacteria

10. Viral Replication
Limited host range – each virus can only infect certain tissues in certain species
Cannot replicate their own genetic material– must occur in host cells
Two major variations studied in bacteriophages – lytic cycle (kills host cell) and lysogenic cycle (lives in host cell)

11. The Lytic Cycle
Bacteriophage injects its DNA into a host cell
Takes over cell’s machinery to synthesize new copies of the viral DNA and protein coats
New viruses assemble in the cell until cell lyses (ruptures) releasing the copies of the virus to infect other cells

12. The Lysogenic Cycle
Bacteriophages DNA becomes incorporated into the host’s DNA
When host replicates its DNA, viral DNA is replicated along with it
Viral DNA called “prophage”

13. Retroviruses
RNA viruses
Use reverse transcriptase to transcribe DNA from the RNA template
New DNA then integrates itself into host DNA
Host then transcribes that DNA into RNA and the viral proteins, creating more of the virus

14. Mutation Rates
RNA viruses do not have error-checking mechanisms – much higher rates of mutation
Mutations accumulate rapidly leading to diverse populations from one original virus
Originally harmless viruses
can become virulent
Difficult to make vaccines
Can also be used to induce
non-virulence

15. Prions
Misfolded, infectious proteins
Cause the misfolding of normal proteins, usually in the brains of infected animals
Damage in the brain accumulates and causes death
Ex. Creutzfeldt-Jakob disease in humans, mad cow in cattle