DD- VIRUS STRUCTURE ANDFX Flashcards
Koch’s postulates viral pitfall
The agent must be isolated from the host and grown in vitro- viruses cannot always do this
The agent must be present in every case of the disease
The agent must be isolated from the host and grown in vitro.
The disease must be reproduced when a pure culture of the agent is inoculated into a healthy susceptible host.
The same agent must be recovered once again from the experimentally infected host.
Koch’s postulates
A virus is a submicroscopic, infectious,______ intracellular parasite
obligate
The genetic material of a virus enters a host cell and directs the production of the:
building blocks of new virus particles
The genetic material of a virus is either _____ and is encased in a protein shell
DNA or RNA
New virions are produced from self-assembly of______ components within the host cell
newly synthesized
The new virions produced in a host cell ______ to another host cell or organism to carry out another round of infection
transport the viral genetic material
Viruses house their DNA or RNA genomes in:
small proteinaceous particles (capsids).
The viral genome contains all the information to______an infectious cycle.
initiate and complete
Viruses establish a relationship that ranges from ____ in a population of hosts
benign to lethal
2 Classification of viruses
The classical system: Linnaean/biological categorization of viruses governed by the ICTV
The Baltimore classification scheme
The classical system:
Viruses grouped according to their shared physical properties (4)
a) Nature of the genetic material in the virion (DNA or RNA)
b) Symmetry of the capsid (helical or icosahedral)
c) Naked or enveloped
d) Dimensions of the virion and capsid
dsDNA Gapped circular DNA ssDNA dsRNA ss(+)RNA ss(+)RNA with DNA intermediate ss(-)RNA
Seven Classes of Viral Genomes
The Baltimore classification scheme
Based on the Central Dogma:
DNA --> RNA -->protein
a) Nature of the genetic material in the virion (DNA or RNA)
b) Symmetry of the capsid (helical or icosahedral)
c) Naked or enveloped
d) Dimensions of the virion and capsid
The classical system: Linnaean/biological categorization of viruses governed by the ICTV
Seven Classes of Viral Genomes
dsDNA Gapped circular DNA ssDNA dsRNA ss(+)RNA ss(+)RNA with DNA intermediate ss(-)RNA
_____protect the genome and serve as a specific genome delivery device
Capsids
Nucleocapsid
Nucleic acid-protein complex in a virion when this is a substructure of a complex particle
Envelope
Host cell-derived lipid bilayer
Capsids assemble from components ______made during infection
(capsid proteins)
Spike
Virus derived membrane-bound glycoproteins
Viruses have evolved two general forms for packaging their genomes
Helical Capsids
Icosahedral Capsids
Both kinds can be surrounded by a lipid envelope
Virion
Infectious virus particle
virally encoded glycoproteins (spikes) function in
- entry and host range determinants
- assembly and egress
- evasion from the vertebrate immune system
During the eclipse to latent period there is a lot going on inside of the cell (5)
Entry
Viral gene expression
Translation of viral proteins
Virus genome replication
Assembly of new viruses and release of virus from the cell
A______ cell has a functional receptor for a given virus–the cell may or may not be able to complete the replication cycle
susceptible
A _______cell has no receptor–it may or may not be competent otherwise to replicate the virus.
resistant
A_______ cell has the capacity to replicate virus–it may or may not be susceptible
permissive
A _________ cell is the only cell that can take up virus and replicate it
susceptible AND permissive
Virus attachment to the cell surface
At least two steps are involved:
- Non-specific, electrostatic binding places viruses in close proximity to cell surface.
- Proteins on the virus particle must interact with proteins on the cell membrane to initiate the entry process.
gain access into different tissue types
entry of virus into a single cell: co-receptors.
combination of carbohydrate and protein receptor molecules
these are examples of:
viruses use more than one receptor
