Viruses and Prions Flashcards
viruses are
submicroscopic infectious particles
virus characteristics
acellular (no cells)
obligate intracellular pathogens
DNA or RNA
infect all known life
no metabolism
when were viruses discovered
1898
virus size
20 - 1000 nm long
virion
single infectious virus particle
virion parts
exterior protective protein capsid
genetic material
capsid
protein shell
bulk of a vision
capsomere subunits
animal viruses can be
helical
icosahedral
complex
bacteriophage
complex capsids
attach to cell surface to inject genetic material
envelope
lipid-based
arises from budding off host cell
animal viruses may be enveloped
bacteriophages are not enveloped
naked (nonenveloped)
viruses that lack an envelope
cell lysis (bursting)
spikes
peplomers
protrusions from capside or envelope
glycoproteins
aid in attachment and entry to host cell
glycoprotein
proteins with sugars
stages of animal virus replication
- attachment
- penetration
- uncoating
- replication
- assembly
- release
attachment
naked viruses attach to host cells using capsid proteins
other viruses use spike proteins
host range
collection of species a virus can infect
tropism
range of tissues or cells a virus can infect inside a given host
specificity - “lock and key”
penetration
enveloped - endocytosis or fusion
naked - endocytosis
uncoating
capsid is digested by enzymes
replication needs to do 2 things
- replicate nucelic acid
- produce new structural proteins
DNA virus replication
replicates DNA and makes RNA
RNA produces viral proteins
proteins and new DNA make virions
RNA virus replication
RNA makes new proteins
RNA-dependent RNA polymerase produced more RNA molecules
these work together to build new virion
retrovirus (RNA)
reverse transcriptase to produce DNA
then follows DNA replication process
assembly
formation of new virions
packaging of genome
release
enveloped - budding
naked - lysis of host cell
viral infection types
acute
chronic
latent
systemic
acute infection
continuous viral replication
chronic infection
slow release of viral particles
may or may not kill host cell
latent infection
acute, but virus enters quiescent period (dormant)
no new viral progeny produced
reactivation
systemic infection
in plants
the plant rarely recovers
oncogenic viruses
causes ~ 10 - 15% of cancers
stimulate uncontrolled host cell division
decreases host cell responsiveness to death signals
ex. HPV
what do bacteriophages infect
bacteria
bacteriophage replication
lytic or lysogenic
lytic replication pathway
- adsorption
- penetration
- replication
- assembly
- maturation
- release
temperate phages
can be lytic or lysogenic (both are possible)
lysogenic replication pathway
- adsorption
- penetration
- integration (cell division or lytic cycle entry)
- replication
- assembly
- maturation
- release
integration
prophage - viral genes in host chromosomes
prophage conversion
confer new pathogenicity factors to bacteria
prions
infectious, misfolded proteins
prion characteristics
no genetic material
do not replicate in classical sense
made from proteins most abundant in brain
what do prions cause
transmissible spongiform encephalopathies
prions in sheep cause
scrapie
prions in cows cause
bovine spongiform encephalopathy (BSE)
“Mad Cow Disease”
prions in humans cause
kuru (from cannabalism)
Creuzfeldt-Jakob disease (CJD)
prions come from
PrPC (made by all mammals)
prions form
amyloids - abormal aggregates
infectious form on PrPC
PrPSc
prion transmission
acquired - direct exposure
genetic - familial
sporadic - unknown (85% of cases)
