Bacteria & Archaea and Viruses Chapters 27 and 19

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

*Structurally different than eukaryotic flagella – analogous structures*

Reproduce by Binary Fission Short reproduction times

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

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+

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

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

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

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)

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

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”

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

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

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