Virus structure and function Flashcards
Property of virus
submicroscopic, obligated intracellular parasite, uses host to replicate ans assemble progeny
Viral Classical system:
Nature of genetic material (DNA/RNA)
Symmetry of capsid
Naked/enveloped
Dimensions of virion/capsid
Baltimore system viral calssificaiton based on:
Central dogma (DNA, RNA, Proteins)
Baltimore first principle
Small finite number of nucleic acid copying strategies
Baltimore second principle
Viral genome in cell makes mRNA (viral genome must provide mechanisms for syn of mRNA)
7 classes of viral genome configuration
dsDNA gapped circular dsDNA ssDNA dsRNA ss+ RNA ss- RNA ss+ RNA with DNA intermediate
3 main function of virion proteins
protection of genome
Delivery of genome
Mediate interaction with host
Two hypes of capsids
helical and icosahdral
Helical capsids arranged by:
identical subunits - rotational symmetry/irregularly shaped protein –> disk
Icosahedral capsids are:
form hollow quasi-spherical structure with genome inside.
Envelopes - define and source
lipid bilayers during assembly/budding - with viral glycoproteins embedded
plasma membrane, ER, golgi
Envelope functions
entry and host range determination
Assembly/egress
Evasion from immune sys
Describe growth curve of virus life cycle
One step
Eclipse phase
Latent period
plaque forming units shoots up after latent period
Eclipse period:
particles broken down, release genome
No PFU - Not infectious
Latent period
Time from initiation of infection to release infectious virus particle from cell
5 main things happen during latent period:
attachment of virus to cell
Entry of virus into cell/uncoating of viral genome
Viral gene expression
viral genome replication
assembly of new virus/egress to new particles
Carbohydrate receptor tend to be _____ ______ than protein receptor (and why)
less specific
Same config of carb side chain on many diff glycosylated membrane bound molecules
Entry is an energy ______ process
dependent (cell must be metabolically active)
2 ways for virus to enter cell
endocytosis -> nedosomes -> escape
Enveloped -> fusion with cell membrane
Uncoating (define)
viral particle enter cell, capsid removed, genome exposed
Gene expression for DNA virus
ds, gapped, ss = transcribe mRNA using (-) strand as template
Uses: Host RNA pol II (nucleus)
mRNA capped/poly adenylated
Poxviruses are unqiue in their gene expression - why?
replicate in cytoplasm - encodes own RNA polymerase
All RNA viruses make an viral enzyme called ____________?
RNA-dependent RNA polymerase (RdRp)
RdRp function
production of mRNA and replication of RNA genomes
+ vs - strand RNA virus gene expression
+ = translated directly by cellular ribosomes. Amp of mRNA copy number/subgenomic mRNA by RdRp
- = transcribe + mRNA
package RdRp in virus particle
Retroviruses uses what enzyme?
reverse transcriptase - RNA to DNA - integrate into host - transcribed with host cell encoded RNA pol II
dsDNA viral replicate (location and methods)
- nuclear - cellular factor, viral pol, accessory factors
Cytoplasm - largely independent of cell machinery
ssDNA virus replicate (location)
nucleus
forms ds intermedate - template for syn ssDNA
Gapped circular ds DNA replicate
Virally encoded reverse trasncriptase - mRNA to DNA viral genome
Gaps must be filled in before transcribed
Icosahedral capsids packaging of genome by (1) or (2)
(1) capside assembles around genome
(2) genome fed into preformed capsids
Egress by naked capsids viruses typically ______
cell lysis
Egress by enveloped typically
budding
From plasma membrane - extracellular environment directly
From ER/Golgi - secreted from infected cell
Primary initial routes of virus infection:
respiratory, alimentary, genitourinary
Also: mucous membrane, skin abrasion, parentally
Successful initial infection requires?
Sufficient virus, host susceptible, host permissive, low host defense
Sufficient virus
free virus particle must sruvive environmental exposure/abundant enough in concentration
Tropism defined as:
infect certain tissues and not other - tissue specificity
site of initial replication (local/systemic)
Epithelium both
Secondary replication sites (local/system)
none
lymphoid organs, lungs, skin
Incubation and immunity (local vs systemic)
1-3 days vs 10-21 days
Short vs lifelong
Antibody to resist acute local/systemic?
Local: IgA
Systemic: IgG and IgA
Chronic viral infection described as
ongoing infection/replication with mild/inapparent disease
Persistent vs latent
continue to produce new virus vs No infection detected but can reactivate/recrudescence
Slow chronic infection
no symptoms initially, long incubation, may induce immune response. Eventually deterioration/death
Example of acute local, systemic, chronic, latent, slow
cold/diarrhea Smallpox/measles Rubella VZV AIds, cancer
Transforming viral infection: define
integrate to host -> activate/supress oncogene/TSG
Tumorigenesis
