1 - Intro to Virology Flashcards
Viruses are obligate intracellular parasites, what does this mean?
They rely on host metabolic machinery and protein biosynthetic machinery.
“autonomy” from host cell enzymes varies widely among viruses.
Describe the virion size, structure, and genome?
Diameter from ~300 nm to ~20 nm and are filtrable agents best viewed by electron microscopy.
Can be enveloped with membrane or naked.
Genome can be DNA or RNA.
Describe the intracellular and extracellular phase that a virus goes through?
Intra: transcription, replication, synthesis of new proteins, assembly of virions within infected cell.
Extra: particles must pass from cell to cell or throughout body, between individuals, or between individuals and insect vectors.
What is the size of a virus compared to a cell?
100 to 1000x smaller than a cell.
The taxonomic method used in virology is ______? What does this mean?
Polythetic:
- any virus is described using a collection of individual properties
- members always have several but not all properties in common
What is the polythetic taxonomic method important for?
Diagnosis Identification of new viruses Clarification of life cycle Drug use and design Vaccine development
What are the five properties used for classification?
- Particle type: icosahedral, filamentous, irregular proteins capsid. Membrane enveloped or naked.
- Genome type:
~RNA: + sense (mRNA), - sense ds, segmented.
~DNA: ss, ds, linear, circular - Tissue tropism
- Disease etiology
- Serology
Describe the different particle types that viruses may have? What function does this serve?
Capsids from one or more proteins w/ repeating protein-protein contacts.
Capsids can form naked viruses or be surrounded by a membrane for enveloped viruses (matrix protein lies under envelope)
Capsid/envelope are the delivery vehicle during transmission.
What are two examples of viruses that are icosahedral and non-enveloped?
Adenovirus and papillomavirus (dsDNA)
What are examples of an icosahedral enveloped viruses and a helical enveloped virus?
Icosahedral/enveloped: Herpes simplex virus
Helical/enveloped: paramyxovirus
What is the major difference between having a naked and enveloped virus?
Exposed proteins on the capsid and membrane are targets of neutralizing antibodies.
Naked are more stable and can last longer on surfaces than enveloped viruses can because lipid envelopes break down.
Antibodies against viral antigens are used in serology assays for diagnosis.
For viral genome typing, what is the Baltimore classification? Describe types I-IV
Classification provides initial understanding of how a given virus will replicate
I: dsDNA II: ssDNA III:dsRNA IV and V: ssRNA - IV is positive sense - V is negative sense
Icosahedral RNA viruses can be ____ or _____, while helical RNA viruses are all ______.
Icosahedral can be naked or enveloped.
Helical are all enveloped.
For DNA viruses, describe the structure of icosahedral, helical, and complex viruses?
Icosahedral can be naked, enveloped, or naked/enveloped (cytoplasmic)
Helical are all enveloped.
Complex are all enveloped (cytoplasmic).
What is a virion? What is a virus? What is viremia? How are viruses visualized?
Virion: a viral particle
Virus: an infectious particle
Viremia: spread of virus throughout the body via the bloodstream
Seen via electron microscopy.
What is MOI? What is CPE? What is infectivity?
MOI: multiplicity of infection (virus/cell)
CPE: cytopathic effect, structural changes in host cell caused by viral invasion
Infectivity: infectious particles / non-infectious particles
How are viral infections quantified?
Plaque assay: titration of # of infectious progeny per volume (plaque forming units)
Focus forming assay: for viruses promoting cell proliferation rather than death
Single-step growth curve: provides quantitation of ‘burst size” (put one particle in and determine how much virus is coming out of that system).
What are tissue culture models of infection?
Cytopathic effect Cytolytic effect Transforming (oncogenic effect) Induction/production/release of diagnostic enzymes Expression of diagnostic antigens
What do naked capsid viruses contain? What do enveloped viruses contain?
Naked capsid: DNA or RNA + structural proteins +_ enzymes and nucleic acid binding proteins = nucleocapsid
Enveloped: Everything listed above + glycoproteins and membrane
What are components of a virion particle? What is the dilemma they’re faced with?
- Genome
- Enzymes (none or many)
- Auxillary proteins for assembly, blocking immune response, and disassembly
- Structural proteins
- Attachment proteins
- Fusion proteins
- membrane
Need a particle that’s stable enough to survive outside the host, but that can be effectively disassembled during the next round of infection.
What does a sucessful virus need to be able to do?
- Initiate infection
- Replication/macromolecular synthesis
- Virus assembly and egress (release from cells)
- Hold host at bay long enough to undergo replication
What are the basic steps in a viral life cycle?
- Recognition
- Attachment
- Penetration
- Uncoating
- Transcription
- Synthesis of components
- Genome replication
- Assembly of viral components
- Exit/maturation
What is involved in virion attachment?
- Viral surface proteins
- Both naked and enveloped viruses
- Recognizes a cell receptor on the target cell - Cell surface receptors
- Protein or carbohydrate
- Can determine species, tissue and/or cell tropism
What are the components of virion entry?
- Naked virus: enter cell via endocytosis, and are surrounded by an endosomal membrane.
- Enveloped virus: fusion or virus and cell membranes releases capsid into the cytoplasm. Acidification of compartment results in membrane fusion and capsid release.
