Ch. 20

• A virus is a microscopic pirate associated with disease, host-specific, and is an obligate intracellular parasite
• Viruses have nucleic acids but require a host to replicate, lacking metabolism or other characteristics of life
• Viruses are classified based on size/shape, type of nucleic acid, and the presence of an outer envelope with virally-encoded protein spikes for cell entry
• Structure of a virus includes an outer protein capsid, nucleic acid inner core, and may have an envelope acquired from the host
• Example: Coronavirus is an RNA virus with an envelope and spikes, belonging to the Corona family with crown-like spikes
• Reproduction of a virus involves standard steps like attachment, penetration, biosynthesis, maturation, and release
• Variations in viral reproduction include lytic and lysogenic cycles, with bacteriophages having two alternative life cycles
• Animal viruses can enter cells in various ways, uncoat their genome, and replicate through lytic or lysogenic cycles
• Retroviruses like HIV convert RNA into DNA within host cells, remaining latent and can be targeted by antiretroviral drugs
• Emerging viruses cause new or uncommon illnesses due to range extension or genetic mutations, increasing virulence factors
• Viroids are naked RNA strands causing crop diseases, while prions are misfolded proteins causing TSE diseases like mad cow disease
• Prophages stay latent by injecting viral DNA into host DNA, expressing during stress for replication
• Virulence measures a virus's pathogenicity, and concerns include rapid evolution, climate sensitivity, and research at institutions like Harvard
• Prokaryotes have a typical structure including cell envelope, cell wall, plasma membrane, cytoplasm, ribosomes, and appendages like flagella
• Reproduction in prokaryotes occurs through binary fission, allowing quick genetic variation and recombination through conjugation, transformation, and transduction
• Bacteria characteristics include cell wall composition, cell shapes, growth arrangements, and various metabolic types like autotrophic and heterotrophic bacteria
• Antibiotics inhibit protein synthesis or cell wall formation/repair, but overuse can lead to stronger bacteria through artificial selection
• Cyanobacteria are important for oxygen production and can form symbiotic relationships, while Archaea differ from bacteria in cell membranes and walls