CPA #14 Questions Flashcards
why are viruses acellular?
noncellular; no cytoplasmic membrane; no cytosol or functional organelles
why are viruses not considered living?
cannot carry out metabolic pathways; cannot grow; cannot respond to environment; cannot reproduce independently
define: envelope
phospholipid membrane surrounding nucleocapsid
define: capsid
protein coat surrounding a nucleic acid core
define: virion
extracellular state of virus; made of capsid and envelope; (capsid/envelope help to protect and provide recognition sites that bind to complementary chemicals on host cells)
explain the experiment to prove viruses are acellular
1892; russian microbiologist Dmitri Ivanowski; cause of tobacco mosaic disease; filtered sap of infected tobacco plants through porcelain filter small enough for the smallest of cells; virus passed through with the liquid, still infecting plants, proving that viruses lacked cells
what are the five steps of lytic replication
- attachment
- entry
- synthesis
- assembly
- release
define: attachment
virion attaches to host cell
define: entry
virion or genome enters host cell
define: synthesis
nucleic acids and proteins are synthesized by host cells enzymes and ribosomes
define: assembly
new virions are assembled in host cell
define: release
new virions are released from host cell; killing host cell
how is lysogenic replication different than lytic?
bacteriophages in lysogenic replication where infected host cells grow and reproduce normally for multiple generations before they lyse; aka lysogeny; phages = temperate phages or lysogenic phages
define: induction
the trigger for the lytic cycle to start
what are the 3 mechanisms of animal viral entry?
- direct penetration
- membrane fusion
- endocytosis
define: direct penetration
poliovirus; capsid attaches and creates porin cytoplasmic membrane; genome alone enters and capsid stays on surface
define: membrane fusion
measles; viral envelope and host cytoplasmic membrane fuse; release capsid into cells cytoplasm; envelope glycoproteins stay on cell membrane
define: endocytosis
adenovirus (naked) & herpesvirus (enveloped); attachment of the virus to receptor molecules on cell surface stimulates the cell to endocytize the virus
what is the genetic material in retroviruses?
dsDNA from ssRNA
how do retroviruses replicate?
reverse transcriptase transcribes dsDNA from the ssRNA genome which then serves as a template for the synthesis of additional ssRNA molecules which act as both mRNA and as a genome; HIV
define: budding
process of how enveloped animal viruses are released; virions are extruded through one of the cells membranes
define: persistant infection
host cells shed a virus slowly and steadily to allow infected cell to stay alive longer
define: latency
virus remains dormant; latent or proviruses; can be prolonged for years without activity, signs, or symptoms
what percent of cancers do viruses contribute to?
20-25%; viruses may carry copies of some oncogenes as part of genome; viruses may insert near to and promote oncogenes that are already present; viruses may interfere with normal tumor repression
what are the three types of ways that viruses can be cultured?
- media consisting of mature organisms
- embryonated eggs
- cell cultures
why cant viruses be cultured in a test tube?
viruses cannot metabolize or replicate by themselves
define: plaques
areas of a bacterial culture where the phages have lysed the bacteria; appear clear
define: plaque assay
plaque corresponds to a single bacteriophage spreading and multiplying through the original bacterium-virus mixture
why is culturing viruses in animals difficult?
maintaining lab animals can be difficult and expensive; raises ethical complications
why are chicken eggs used to culture embryos?
inexpensive; among the largest of cells; free of contaminated microbes; contain a nourishing yolk which makes them self sufficient
define: viroid
extremely small circular pieces of ssRNA that are infectious and pathogenic in plants
define: prion
proteinaceous infective particles; lacks instructional nucleic acid
describe how contaminated meat can be treated and safe to eat?
heating to 482C for 4 hours or autoclaving at 132C in concentrated sodium hydroxide for 1 hour; treatment with a 10% solution of phenolic compounds for 1 hour
how are prion associated diseases treated?
no standard treatment; some drugs hold promise
define: HeLa cells
derived from Henrietta Lacks who died from cervical cancer in 1951; continuous cell culture that allows for studies on cell metabolism, aging, and viral infection; unethical because of the money that was made off of these cells without her knowing they even took them
how do prions replicate
PrP protein that misfolds, causes other PrP proteins to misfold, creating a sticky structure and cause holes
define: naked virion
Extracellular state of virus; no envelope
