Bacteria & Archaea and Viruses - PowerPoint Presentation

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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 reproductionHow horizontal acquisition of genetic information occurs in prokaryotes via transformation, conjugation, and transductionHow these mechanisms plus mutation contribute to genetic diversity in prokaryotesThe components of a virusThe differences between lytic and lysogenic cyclesHow viruses can introduce genetic variation into host organismsMechanisms that introduce genetic variation into viral populations

*Structurally different than eukaryotic flagella – analogous structures*

Reproduce by Binary FissionShort reproduction times

Genetic Diversity

Transformation – a prokaryote takes up DNA from its environmentTransduction - Bacteriophage virus transfers genes from one prokaryote to anotherConjugation - Genes directly transferred from one prokaryote to another by a mating bridge formed by connected piliHorizontal gene transfer = between different speciesMutations – rare, but main source of genetic diversity in bacteria

Nutritional and Metabolic AdaptationsObligate aerobes – require oxygen (use cellular respiration)Obligate anaerobes – oxygen kills them, use fermentationFacultative anaerobes – use oxygen if available, but can do fermentationNitrogen fixation - some prokaryotes can use atmospheric nitrogen directly – covert N2 to NH4+

ArchaeaMany 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 HumansPathogens – produce poisons that kill infected organismAntibiotics – kill prokaryotes but not virusesMany bacterial plasmids contain genes for resistanceBioremediation – removal of pollutants from soils, air, or water using prokaryotesSymbionts – live in gut, produce vitamins and help digest foodProduction of cheese, yogurt, etc

Structure of a virusSmaller than ribosomes – about 20nmComposed 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 ReplicationLimited host range – each virus can only infect certain tissues in certain speciesCannot replicate their own genetic material– must occur in host cellsTwo major variations studied in bacteriophages – lytic cycle (kills host cell) and lysogenic cycle (lives in host cell)

The Lytic CycleBacteriophage injects its DNA into a host cellTakes over cell’s machinery to synthesize new copies of the viral DNA and protein coatsNew viruses assemble in the cell until cell lyses (ruptures) releasing the copies of the virus to infect other cells

The Lysogenic CycleBacteriophages DNA becomes incorporated into the host’s DNAWhen host replicates its DNA, viral DNA is replicated along with itViral DNA called “prophage”

RetrovirusesRNA virusesUse reverse transcriptase to transcribe DNA from the RNA templateNew DNA then integrates itself into host DNAHost then transcribes that DNA into RNA and the viral proteins, creating more of the virus

Mutation RatesRNA viruses do not have error-checking mechanisms – much higher rates of mutationMutations accumulate rapidly leading to diverse populations from one original virusOriginally harmless viruses can become virulentDifficult to make vaccinesCan also be used to induce non-virulence

PrionsMisfolded, infectious proteinsCause the misfolding of normal proteins, usually in the brains of infected animalsDamage in the brain accumulates and causes deathEx. Creutzfeldt-Jakob disease in humans, mad cow in cattle