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Disease & Defense - Unit 3 > Viral Structure and Function > Flashcards

Flashcards in Viral Structure and Function Deck (22):

Basic properties of viruses

-obligate intracellular bacteria
-not alive; do not undergo division
-virus replicates and reassembles w/in a host cell


Viral strategies for survival

-house DNA or RNA genomes in small proteinaceous particles (capsids)
-genome contains info to carry out infectious cycle
-establish relationships w/population of hosts from benign to lethal


Major classification systems of viruses

-classical system: viruses grouped according to shared physical properties
-baltimore system: based on the central dogma (based on how they produce mRNA)


Criteria for classification via classical system

1. nature of genetic material (DNA vs. RNA)
2. symmetry fo the capsid (helical vs. icosahedral)
3. naked vs. enveloped
4. dimensions of the virion and capsid


Methods for studying viruses (5)

-electron microscopy
-animal models
-sequence analysis
-cell culture


Key principles of viral genomes (2)

-genomes are templates for synthesis of progeny genomes; thus there is finite number of nucleic acid copying strategies
-viral genome goal inside host is to make mRNA (that will be translated by host protein synthesis machinery); genomes must provide mechanisms for synthesis of mRNA


Classes of viral genome configuration (7)

-gapped circular dsDNA
-ss(+)RNA w/DNA intermediate


Functions of virion proteins (3)

1. protect genome: recognize and package genome, assemble stable protein shell, interact w/ cell membrane if envelope formation needed
2. deliver genome: bind receptors, uncoat genome, induce fustion w/host cell membrane, direct transport of genome to appropriate site
3. mediate interactions w/host


General characteristics and types of capsid proteins

-symmetrical arrangement of identical/highly similar proteins
-NON-COVALENT bonds (allows for stable assembly and ready reversal during genome delivery)
-sub-units are self-assembled by engaging in "identical" bonding contacts w/neighbors
-helical capsids
-icosahedral capsides


Helical capsid properties

-multiple identical subunits arranged using rotational symmetry
-irregularly shaped proteins arranged around a circumference of a circle to form a disk


Icosahedral capsid properties

-hollow, quasi-spherical structure
-20 traingular faces w/12 vertices
-faces w/2-,3-, and 5-fold symmetry


Properties of enveloped viruses

-envelope=lipid bilayers acquired during assembly of viral particles; usually have viral glycoproteins w/in membrane
-usually acquired through budding through a membrane of host
-don't necessarily kill host cells in the course of replication


General stages of "one-step growth curve" experiment

-every cultured cell is infected w/virus
-eclipse period (~0-12hrs): virus particles have broken down after penetrating cells; no detectable virus
-latent period: time between infection and release of new infections virus particles from the cell


Processes taking place during latent period

1. attachment of virus to cell: virus-attachment protein binds to receptor
2. entry of virus into cell; uncoating of genome: energy-dependent, endocytosis, fusion (enveloped viruses)
3. viral gene expression
4. genome replication
5. assembly of new viruses
6. egress of new virus particles from cell


DNA virus gene expression strategy

-must transcribe mRNA using (-) strand of the DNA genome
-uses host RNA pol II to fill gaps/replicate DNA and produce mRNA


RNA virus gene expression strategies

-use viral enzyme RNA-dependent RNA pol (RdRp) for production of mRNA and replication of RNA genomes


(+)RNA viruses gene expression strategy

genome may be directly translated by host ribosomes; RdRp is coded by and then replicates genome


(-) RNA viruses gene expression strategy

-must transcribe (+)sense mRNA to express genes
-package RdRp w/in virus particle


Retrovirus ((+)RNA w/DNA intermediate) gene expression strategy

-copy ssRNA into dsDNA via virus particle reverse transcriptase
-dsDNA incorporated into host genome
-host RNA pol II transcribes host genome into mRNA


Viral genome replication strategies

-dsDNA: nuclear or cytoplasm
-ssDNA: nucleus. ds intermediate=template for ssDNA synthesis
-gapped circular dsDNA=viral reverse transcriptase to take viral mRNAs --> DNA
-RNA: RdRp. genome replicated using antigenome as a template


Viral assembly strategies

a. capsid assemble around genome
b. genome fed into preformed capsids
-helical: genome coated w/capsid protein during synthesis


Viral egress strategies

-naked: lysis
-enveloped: budding through a. cytoplasm --> extracellular environment or b. cytoplasm --> golgi/ER --> secreted from cell