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30 Cards in this Set
- Front
- Back
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notable characteristics about viruses
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miniscule, acellular, has DNA or RNA (never both), causes most diseases, can infect humans, animals, plants, bacteria.
can't metabolize, grow, respond to environment, reproduce independently. does not have organelles, cytosol, sytoplasmic membrane. |
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extracellular state vs. intracellular state of virus
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extracellular:
- called virion - has capsid (protein coat) that surrounds nucleic acid. - nucleic acid + capsid = nucleocapsid - might have phospholipid envelop (taken from a host that gives it protection & recognition sites) intracellular: - capsid removed - only nucleic acid |
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Virus may be specific or generalist (explain & give example)
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specific: only infects particular host/particular cell in particular host (ex: HIV only infects human's helper T cells)
generalist: can infect many different hosts/many different cells in host (ex: influenza) |
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capsomeres
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proteinaceous subunits that make up a virus' capsid
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matrix proteins
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proteins that are found in between the capsid & the envelope of an enveloped virus
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viral envelope
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- acquired from host during replication or release
- composed of phospholipid bilayer & proteins (some code for glycoproteins) - host recognition of envelop allows virus to attach |
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lytic replication
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usually results in lysis of host cell
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stages of lytic cycle
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attachment, entry, synthesis, assembly, & release
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burst time
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period of time from synthsis to release
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burst size
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number of new virions released when one host cell bursts
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lysogenic cycle
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uses temperate or lysogenic phages.
can be carried in host's genome for generations before abnormalities occur & they lyse. |
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prophage
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inactive phage
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lysogenic conversion
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phage carries genes that alter phenotype of host
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animal viruses are different from bacteriophages b/c:
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envelop on some viruses,
eukaryotic cell nature of animals, no cell wall in animals |
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3 attachment types in animal cells
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chemical attraction,
animal viruses do not have tails or tail fibers, glycoprotein spikes mediate attachment (or other attachment molecule) |
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3 entry types into animal cells
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direct - receptors on cytoplasm allow phage to insert genome & capsid stays outside
membrane fusion - viral envelop stays in membrane & capsid uncoated in host cell endocytosis - entire virus engulfed by host cell & capsid then uncoated |
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DNA viruses replicate in the nucleus except
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poxvirus replicates in the cytoplasm
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dsDNA replication
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makes mRNA, then makes viral proteins
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ssDNA replication
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makes complementary DNA strand, binds to initial DNA strand, then makes mRNA to make proteins
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retrovirus replication
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starts w/ positive ssRNA,
do not use genome as mRNA, synthesizes DNA from positive RNA by reverse transcriptase enzyme, DNA acts as template for +mRNA advantage: better integration! |
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number of viruses produced by lysis of host cell depends on:
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initial health of host
type of virus & host cell size of virus & host cell |
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Budding
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occurs when virus exits host cell and takes some host's cytoplasmic membrane w/ glycoproteins with it to aquire a viral envelope.
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Latency
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occurs when virus remains dormant in host cell.
may last for years & some may not be incorporated into host's DNA, but incorporation is permanent. Ex: herpes & chicken pox |
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The best way to culture viruses
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in chicken eggs!
b/c: inexpensive, large, free of contamination, nourishing yolk. |
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Cell/Tissue culture (2 types)
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diploid - from embryonic cells & doesn't last over 100 generations
continuous - lasts longer, from tumor cells. Ex: HeLa |
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Viroids
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small, circular RNA
infectious to plants NO capsid may appear linear b/c hydrogen bonding |
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Prions
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discovered in 1982 by Stanley Prusiner.
lack nucleic acid, make cellular PrP (alpha-helices) into prion PrP (beta-sheets) to cause disease |
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cellular PrP
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all mammals have this protein in cytoplasmic membrane that contributes to brain activity
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diseases caused by prions
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fatal brain degeneration,
fibril deposits, loss of brain matter, large vacuoles, characteristic spongy appearance! |
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prions can only be destroyed by
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autoclaving in 1 N NaOH & incineration
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