Ch 13 Viruses Part 2 Flashcards
how do animal phages differ from bacteriophages
the mechanisms of entering the host cell are different as well as the synthesis and assembly of new viral components
what are the five stages of multiplication of animal viruses
1)attachment 2)entry 3)uncoating 4)biosynthesis 5)maturation/release
describe attachment in animal viruses
receptor sites are proteins and glycoproteins
receptor sites are inherited characteristics of the host
varies from person to person (susceptibility)
describe entry in animal viruses
receptor mediated endocytosis
fusion
this is how viruses enter eukaryotic cells
molecules bound to proteins on the plasma membrane are take in by infolding of the membrane
receptor mediated endocytosis
viral envelope fuses with the plasma membrane and releases the capsid into the cell’s cytoplasm
this is how enveloped viruses enter
fusion
describe uncoating in animal viruses
separation of the viral nucleic acid from its protein coat once the virion is enclosed within the vesicle
capsid is digested when the cell attempts to digest the vesicle’s contents
describe biosynthesis of DNA viruses
DNA containing viruses replicated DNA in nucleus of host by viral enzymes and synthesize capsid into cytoplasm with host enzymes
proteins then join with newly synthesized DNA to form virions (transported to ER)
what are the four steps of biosynthesis of DNA viruses
1) transcription then translation
2) synthesis of capsid proteins
3) maturation occurs in nucleus
4) complete virions are released
DNA virus
causes acute respiratory disease (common cold)
adenoviridae
DNA virus
skin leisons (pus filled)
small pox/cow pox
poxviridae
DNA virus
appearance of cold sores
HHV-1
herpeseviridae
DNA virus
warts, tumors, cytoplasmic vacuoles
capable of transforming cells/causing cancer
papovaviridae
DNA virus
cause hepatitis
hepadinaviridae
describe biosynthesis of RNA viruses
several different mechanisms of mRNA formation occur
RNA viruses multiply in the host cell’s cytoplasm
major difference lies in how much mRNA and viral RNA are produced
(once RNA is synthesized maturation is similar)
this is RNA within a virion that can act as mRNA
translated into two proteins which inhibit host synthesis of RNA (catalyze other strands of RNA)
sense strand or positive strand
template to produce additional positive strands
antisense strand or negative strand
single strand of RNA
contain RNA dependent RNA polymerase that uses negative strand as a template to produce positive strand
rhabdoviridae
respiratory and digestive systems of humans
viral mRNA is produced in the cytoplasm
reoviridae
enveloped viruses
single positive strand of RNA
two types of mRNA are transcribed from the negative strand
togaviridae
carry reverse transcriptase
provirus
retroviridae
uses viral RNA as a template to produce complementary double stranded DNA
reverse transcriptase
never comes out of the chromosome
viral DNA that is integrated into the host cell’s DNA
provirus
describe maturation and release in animal virus
assembly of protein capsid
most capsids of animal proteins are enclosed by envelope
budding
what is the envelope protein encoded by
viral genes which are incorporated into the plasma membrane of the host
process whereby the envelope develops around the capsid
budding
what are the two methods of release
1) assembled capsid pushes through membrane
2) nonenveloped viruses are released through ruptures in host plasma membrane
viruses can alter properties via what
mutation and genetic reassortment
virus may become more viralent
virus may become easily transmitted
mutation
occurs in segmented viruses
these have genomes divided into different segments (code for different info)
two viruses infecting the same cell
responsible for antigenic shift and antigentic drift
genetic reassortment
what can plant viruses be recognized by
pigment loss, marks on fruit/leaves, tumors, and stunted growth
do plants generally recover from viral infections
no
are all infections bad
no
what type of viruses are most plant viruses
RNA
what does plant virus transmission require
mechanical damage to plant
- viruses DO NOT attach to specific cell receptors
- viruses infect plants through wound in plant cell wall
what are virions transferred by
wind, animals, seeds, tubers, soil and pollen
what are the most important agents of transmission
insects that feed on plants (act as vectors)
their feeding by passes cell wall protection and leaves wound that viruses can infect through
what are many plant viruses resistant to
inactivation
what does infection spread from cell to cell through
plasmodesmata
describe replication in plant viruses
similar to animal viruses capsid remains outside the cell filamentous, RNA virus RNA replication and polymerase new virions assemble spontaneously
group of pathogens much smaller and distinctly different from viruses
virions
what do viroids consist of
small, circular, single stranded RNA molecule
NO protein coat (resistant to proteases)
is a single viroid capable of infecting a cell
yes
what is circular and resistant to nuclease digestion
viroid RNA
do viroids act as mRNA molecules
no
how do viroids replicate
autonomously in susceptible cells
RNA is replicated by rolling circle method using host RNA polymerase
all identified viroids do what
infect plants: mechanism unknown, some latent diseases/infections
these are proteinaceous infectious agents
prions
these are linked to a number of fatal human diseases
prions
what type of disease do prions cause
brain degeneration, brain tissue develops sponge-like holes
symptoms may bot appear for years after infection
what is currently thought about prion proteins(PrP)
they are present in normal form in host animals and exposure to altered PrP causes diseases
how did prions arise
following mutation to gene encoding normal PrP
what did the mutation of PrP cause
protein to have different folding properties
the mutated protein is resistant to proteases
resists UV light and nucleases due to lack of nucleic acid
what are prions inactivated by
chemicals that denature proteins
