Viruses 2 Flashcards
importance of viruses of prokaryotes
they can be used to kill bacteria - bacteriophages
genome of viruses of prokaryotes
majority are double stranded
how do we detect viruses
biochemical (enzymatic assays and PCR and NA hybridization), serological (IF, IP, IB, ELISA, RIA), electron microscopy
do you detect viruses and virions the same way
no
how do you estimate how well virion are doing
if it makes 1% of what it is supposed to make - quantity over quality
what are plaque assays based on
based on CPEs (growth lacking where they grow)
used in bacterial cells to demonstrate viable phage numbers, used to detect total virions in mammalian cells, viral particles must be viable
point here is that it is only used to detect virions which are viable viruses
how are viruses used as tools?
• Molecular and cellular biology
– Manipulate systems to investigate function of cells
• Genetics
– Have contributed to understanding of DNA replication, transcription, translation, transport
• Gene therapy
• Immunology
– Understanding our immune system
do viruses have protein synthesis machinery and division by binary fission
no – they use host’s machinery system
where does protein synthesis for virus occur
in the cytoplasm of the host cell
what are virioids and where are they usually found
infectious, subviral particles
found in plant diseases
type of genome in viroids
small circular single stranded DNA
do viroids encode protein
no but they replicate autonomously
what are pseudovirons
they contain non viral DNA but are infectious and do not replicate
what are defective virus/satellites
they are viral kind of viruses that cannot encode capsid protein so they depend on helper viruses for their propagation(replicating), ssRNA, and DNA
example of a defective virus
Hep D
what does Hep D (delta agent) use as its helper
Hep B
why is Hep D considered “viroid-like”
because it does code for its own protein
are prions viruses
no
properties of prions
proteinaceous and infectious but no NA
where do virophages grow
only in a strain of the mimivirus within the infected amoeba – that can infect us
what is the first virophage discovered and describe it
sputnik: an 18 Kb circular double-stranded DNA, icosahedral virus
what do virus need to do to propagate (to replicate)
– Infect an appropriate host cell
– Use the host cell to generate more of itself
– Get out of the host cell to do it all over again
what are the phases of viral life cycle
- Eclipse phase - infectious virus cannot be seen or recovered from infected cells
- Maturation (there is a lot of it)
- Latent phase - progeny virus accumulates intracellularly but it hasn’t been released yet - ends when free virus is released
when does latent period end
when it becomes extracellular aka when the free virus is released
what are the five main stages of virus life
1) attachment (adsorption)
2) penetration (injection)
3) protein and nucleic acid synthesis
4) assembly and packaging
5) virion release
in the influenza virus, where does transcription and replication occur
nucleus
how does influenza virus get its envelope
by budding out of the cell after its assembly
what type of mechanism occurs in adsorption/attachment stage of virus life cycle
specific and non specific
what is the difference between susceptibility and permissibility
susceptibility - does the cell have the receptor required for the VAP (viral attachment protein) to attach so that the virus can get into the cell
permissibility - does the cell have the machinery needed for the virus to be able to replicate
what determine susceptibility and what are these structures made of
receptors - made of protein, carb, or lipid
what determines host range
interaction
is there just one way for a virus to enter the cell
no there are multiple portals of entry
how do enveloped viruses penetrate into the cell
- Endocytosis -> fusion with cellular vacuoles
- Fusion of viral membrane with cellular plasma membrane (fusion mediated by specific viral protein)
- Other mechanisms
how do non enveloped viruses penetrate into the cell
- adsorptive endocytosis
* other ill-defined pathways
what does it mean for the virus to uncoat once it enters the cell
releases viral genome for functional expression
is a cell susceptible and/or permissible once it gets to the protein and nucleic acid synthesis
- cell is susceptible because virus was able to get into it
- if cell has the ability to make protein and nucleic acid for the virus then it is permissible
what happens in the protein and nucleic acid synthesis stage of viral life cycle
the virus uncoats so it takes off its capsid to expose the nucleic acid so that it can replicate and then enters the eclipse phase
can the infectious particle be recovered once the virus has entered the protein and nucleic acid synthesis phase
no
what happens in the assembly and packaging step of viral life cycle
new viral particles are assembled with the preformed viral particles (in cytoplasm or nucleus)
then in enveloped viruses: viral proteins associate w/ cellular membranes, aggregate in patches –> organize –> bud from cell
can maturation occur after initial assembly
yes – they can even occur after virion are released
when does capsid assembly and encapsidation occur
late steps of replication cycle
what are way in which viruses can be released
budding, cell lysis, poke cells in cell membrane
difference between structural and non structural
structural - all proteins in mature virus particle
non structural - viral proteins in cell but not packaged
how can one cultivate virus seeing that they cannot be grown on an agar plate
– susceptible organisms
– cell culture (10 and transformed cells)
– embryonated chicken eggs
– organotypic raft cultures (growing skin in an incubator)
