Chapter 8 Flashcards
archaea viruses
- great diversity
- major role in oceanic microbiomes
how do archaea viruses differ from eukaryotic and bacterial viruses
in genome, morphology, architecture, and protein encoding
virus
genetic element that cannot replicate independently of a living host
virology
study of viruses
virus particle/virion
- extracellular form of a virus
- exists outside the host and facilitates transmission from host to another
virion make up
nucleic acid genome surrounded by protein coat and, in some cases, other layers of material (phospholipid membrane with viral glycoproteins)
characteristics of viruses
- infectious, acellular, pathogens
- obligate intracellular parasites with host and cell-type specificity
- DNA or RNA genome; never both
- lack genes for reproduction requiring exploitation of host-cell genomes to reproduce
viral genomes are sometimes circular, but most….
linear
RNA viruses that contain ___ can be directly read by ribosomes to synthesize viral proteins
+ssRNA
viruses containing ____ must use the _____ template for the synthesis of _____ before viral proteins can be made
-ssRNA, -ssRNA , +ssRNA
+ssRNA
positive single stranded RNA
-ssRNA
negative single strand RNA
viruses can be classified on the basis of…
the host they infect
new classification schemes call for classification of viruses base on…
nucleic acid similarities
viruses size
usually smaller than prokaryotic cells at 0.02 - 0.3 um
-most viral genomes smaller than those cells
caspid
the protein shell that surrounds the genome of a virus particle
caspid composition
of protein molecules arranged in precise and highly repetitive pattern around the nucleic acid
capsomere
subunit of capsid
-smallest morphological unit visible with an electron microscope
nucleocapsid
complete complex of nucleic acid and protein packaged in virion
enveloped virus
virus that contains additional layers around the nucleocapsid (lipid bilayer with embedded proteins)
-envelop makes initial contact with host
arrangement of nucleic acid and protein coat in a simple virus
RNA assumes a helical configuration surrounded by the protein capsid
-centre is hollow
in ro-shaped viruses, length is determined by ___ and width is determined by ___
length: length of nucleic acid
width: size and packaging of protein subunits
icosahedral symmetry
spherical viruses
-most efficient arrangement of subunits in a closed shell
influenza virus envelop
contains spikes of hemagglutinin and neuraminidase forming a halo of predictions around negatively stained virus particles
ebola virion composition
- helical
- spikes of envelop
- lipid envelope
- membrane associated proteins
- nucleocapsid proteins
if a virion has a _____, they might infect humans
lipid envelope
complex viruses composition
several parts, each with separate shapes and symmetries
-icosahedral head and helical tail
most phages contain ____ genome
dsDNA (double stranded)
enzymes in virions critical to infection
- lysozyme-like
- nucleic acid polymerase
- neuraminidases
lysozyme- like enzymes
- make hole in cell wall
- lysis bacterial cell in later stages of infection to release new virions
nucleic acid polymerase
RNA virus-RNA dependent RNA polymerase, also called RNA replicase
-reverse transcriptase (retroviruses)
neuraminidases
(influenza virus)
- enzymes that cleave glycosidic bonds
- allows liberation of viruses from cell
viruses replicate only in…
certain types oc cells or in whole organisms
what kind of viruses are the easiest to grow?
bacterial viruses
titer
number of infectious units per volume fluid
plaque assay
analogous to the bacterial colony; one way to measure virus infectivity
plaques
clear zones that develop on lawns of host cells
- lawns = bacterial or tissue cultures
- each plague results from infection by a single virus particle
efficiency of plating
used in qualitative virology
number of plaque-forming units is almost always lower than direct counts due to…
- inactive virions
2. conditions not appropriate of infectivity
phases of viral replication
- attachment (adsorption)
- entry (penetration)
- synthesis
- assembly
- release
latent period
eclipse + maturation
-early enzyme, nucleic acid, protein coats
burst size
number of virions released
lambda bacteriophages of e.coli
- head & tail
- dsDNA
- circular
MS2 bacteriophages of e.coli
- icosahedral
- ssRNA
- linear
T7 and T3 bacteriophages of e.coli
- head &tail
- dsDNA
- linear
attachment of virion to host cell is…
highly specific
permissive cells
host cell that allows the complete replication of cycle of a virus
T4 attached to cells via…
tail fibres that interact with polysaccharides on the E.coli cell envelop
attachment of virus to its host cell results in…
changes on both virus and cell surface that facilitate penetration
mechanisms to diminish viral infections in eukaryotes and prokaryotes…
- immune defence mechanisms, RNA interference
- restriction modification systems
- viruses can evade bacterial restriction systems
restriction modification systems
- only effective against dsDNA viruses
- mod. of host’s own DNA at RE recognition sites prevents cleavage of its DNA
mechanisms to diminish viral infections in bacteria
chemical modification of viral DNA (lycosylation or methylation)
-production of proteins that inhibit host cell RE system
T4 genome can be divided into what 3 parts?
early, middle and late genes
early and middle proteins
enzymes needed for DNA replication and transcription
late proteins
head and tail proteins and enzymes required to liberate mature phage particles
packaging of T4 genome
- procurer of bacteriophage head is assembled
- packaging motor is assembled
- dsDNA is pumped into head under pressure using ATP
- after head is filled with DNA, T4 tail, tail fibres, and other components are added
virulent mode
burst size is 100 virions
temperate mode
can undergo a stable genetic relationship within the host
- can also kill through lytic cycle
lysogeny
state where most virus genes are not expressed and virus genome (prophage) is replicated in synchrony with host chromosomes
prophage
virus genome
lysogen
a bacterium containing a prophage
animal virus infection stages
- entire virion enters cell
- eukaryotic cells contain a nucleus which is the site of replication for most animal viruses
- animal viruses contain all know moded of viral replication
- many more kinds of enveloped animal viruses than bacterial viruses
influenza
ssRNA -
acquired immunodeficiency syndrome (AIDs)
ssRNA/dsDNA (retrivirus +)
ebola hemorrhagic fever
ssRNA -
sever acute respiratory syndrome (SARS)
ssRNA +
persistent infections
slow release of virus without causing cell death
latent infections
virus present but not replicating
transformation
tumour cell division
cell fusion
to host cell surface
replication of retrovirus
- entry/un-coating retrovirus
- reverse transcriptase activity
- viral DNA enter nucleus and integrated into the host genome
- transcription by host RNA poly. forms viral mRNA and genome copies
- translation of mRNA for viral proteins
