Viral Structure and Function Flashcards
1
Q
Basic properties of viruses
A
- obligate intracellular bacteria
- not alive; do not undergo division
- virus replicates and reassembles w/in a host cell
2
Q
Viral strategies for survival
A
- 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
3
Q
Major classification systems of viruses
A
- classical system: viruses grouped according to shared physical properties
- baltimore system: based on the central dogma (based on how they produce mRNA)
4
Q
Criteria for classification via classical system
A
- nature of genetic material (DNA vs. RNA)
- symmetry fo the capsid (helical vs. icosahedral)
- naked vs. enveloped
- dimensions of the virion and capsid
5
Q
Methods for studying viruses (5)
A
- electron microscopy
- animal models
- sequence analysis
- cell culture
- serology
6
Q
Key principles of viral genomes (2)
A
- 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
7
Q
Classes of viral genome configuration (7)
A
- dsDNA
- gapped circular dsDNA
- ssDNA
- dsRNA
- ss(+)RNA
- ss(-)RNA
- ss(+)RNA w/DNA intermediate
8
Q
Functions of virion proteins (3)
A
- protect genome: recognize and package genome, assemble stable protein shell, interact w/ cell membrane if envelope formation needed
- deliver genome: bind receptors, uncoat genome, induce fustion w/host cell membrane, direct transport of genome to appropriate site
- mediate interactions w/host
9
Q
General characteristics and types of capsid proteins
A
- 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
10
Q
Helical capsid properties
A
- multiple identical subunits arranged using rotational symmetry
- irregularly shaped proteins arranged around a circumference of a circle to form a disk
11
Q
Icosahedral capsid properties
A
- hollow, quasi-spherical structure
- 20 traingular faces w/12 vertices
- faces w/2-,3-, and 5-fold symmetry
12
Q
Properties of enveloped viruses
A
- 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
13
Q
General stages of “one-step growth curve” experiment
A
- 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
14
Q
Processes taking place during latent period
A
- attachment of virus to cell: virus-attachment protein binds to receptor
- entry of virus into cell; uncoating of genome: energy-dependent, endocytosis, fusion (enveloped viruses)
- viral gene expression
- genome replication
- assembly of new viruses
- egress of new virus particles from cell
15
Q
DNA virus gene expression strategy
A
- must transcribe mRNA using (-) strand of the DNA genome
- uses host RNA pol II to fill gaps/replicate DNA and produce mRNA
