Viruses Overview
the bacteria (that bacteriophages) infect
are often more pathogenic to humans
Viruses have all the following except ________. A. definite shape B. metabolism C. genes D. the ability to infect host cells E. ultramicroscopic size
B. metabolism
Infectious protein particles are called _______. A. spikes B. prions C. satellite viruses D. viroids E. phages
B. prions
plaques
areas where virus infected cells have been destroyed show up as clear, well defined patches in the cell culture
A virus that undergoes lysogeny is a/an _________. A. T-even phage B. Animal virus C. Temperate phage D. Intemperate phage E. DNA virus
C. Temperate phage
Clear patches in cell cultures that indicate sites of virus infection are called ________. A. Viruses B. Colonies C. Plaques D. Pocks E. Prions F. Viroids
C. plaques
Chronic wasting disease is found in
Canada United States Norway Finland Sweden South Korea
Which of the following is incorrect about prophages? A. Present when the virus is in lysogeny B. Formed when viral DNA enters the bacterial chromosome C. Replicated with host DNA and passed on to progeny D. Cause lysis of host cells E. Occur when temperate phages enter host cells
D. Causes lysis of host cell
When phage nucleic acid is incorporated into the nucleic acid of its host cell and is replicated when the host DNA is replicated, this is considered part of which cycle? A. Lytic cycle B. Cell cycle C. Multiplication cycle D. Lysogenic cycle E. Virulence cycle
D. Lysogenic cycle
bacteriophages translates to
"bacteria eating"
Bovine Spongiform encephalopathy also known as
"mad cow" disease
classical CJD is not related to
"mad cow" disease
archaeal viruses are roughly divided into two categories
1. morphologically and genetically unique to archaea 2. clear structural and genetically homologs to bacteriophages and eukaryotic viruses
Giant viruses (2)
1. pandoravirus 2. mimivirus
examples of oncoviruses
1. papillomaviruses 2.herpesviruses 3. Hepatitis B viruses
three classical scenarios of origin for viruses
1. progressive hypothesis (escaped genes) 2. regressive hypothesis 3. virus first
what controls the number of viruses released by the infected cell
1. size of the virus 2. health of the host cell
____ to ____% of bacterial DNA contains
10-20% viral sequences
Bovine Spongiform Encephalopathy mortality rate
100%
what is Creutzfeldt Jakob Disease mortality rate
100%
poliovirus infected cells release
100,000 virions
experts estimate that _____ of cancers are caused by
13% of cancers are caused by viruses
human cell has around _______ genes
21,000 genes
poxvirus infected cells release
3000 to 4000 virions
how many genes in hepatitis B virus
4 genes
how many genes does Escherichia coli contain
4,000 genes
international committee on the taxonomy of viruses
8 orders and 38 families (another 84 families not yet assigned to any order)
How much of the human genome consists of viral sequences 0.8% 1% 5% 7% 8% 10% 15% 20%
8%
____% of the human genome consists of
8% sequences that come from viruses
how many genes in HIV human immunodeficiency virus
9 genes
Classical Creutzfeldt-Jacob disease is ________. A. caused by a chronic latent virus B. initiated by an oncogenic virus C. caused by a viroid D. a spongiform encephalopathy of humans E. also called "mad cow disease"
D. a spongiform encephalopathy of humans
Infectious naked strands of RNA that affect plants are called A. spikes B. prions C. satellite viruses D. viroids E. phages
D. viroids
what two people showed that a disease in tobacco was caused by a virus
Dimitri Ivanoski and Martinus Beijerinck
what do T Even Bacteriophages infect
Escherichia coli
Viroids size
about one-tenth the size of an average virus
inside of a host cell, viruses are
active
Viruses are better described as __ or ___ rather than _______ or ______
active or inactive rather than alive or dead
temperate phage undergoes
adsorption and penetration, but do not undergo replication or release immediately
Variant CJD has strong evidence that
agent responsible for VCJD in humans is responsible for BSE in cows
viruses infect
all types of cells, including bacteria, algae, fungi, protozoa, plants, and animals
Loeffler and Frosch discovered
an animal virus that causes foot and mouth disease in cattle
Chronic Wasting Disease is fetal to
animals and there are no treatments or vaccines
because viruses exhibit specific host specificity, some
animals can allow a virus to grow more readily than others
how could Bovine Spongiform Encephalopathy possibly originated
as a result of feeding cattle meat and bone meal that contained Bovine Spongiform Encephalopathy infected products from a spontaneously occurring cause of BSE or scrapie infected sheep products
oncogenic
cancer causing viruses
6. release
enveloped viruses bud off of the membrane, carrying away an envelope with the spikes. this complete virus or virion is ready to infect another cell
Kuru
epidemic occurrence in the 1950-60s among the Fore people of New Guinea
estimated _____ virus particles on
estimated 10^31 virus particles on earth, which approximately 10 times the number of bacteria and archaea combined
regressive hypothesis
existing viruses may have evolved from more complex organisms that lost genetic information over time
Chronic Wasting disease does not appear to
naturally infect cattle or other domesticated animals
Bovine Spongiform encephalopathy is a
neurodegenerative disorder that rapidly progresses
Creutzfeldt-Jacob disease
neurodegenerative disorder that rapidly progresses
prions are _________ infectious agents
noncellular
budding of the enveloped viruses causes
them to be shed gradually without the sudden destruction of the cell
(lysogenic cycle) temperate phages: viral DNA enters an inactive prophase state, which is
then inserted into the bacterial chromosome and copied during the normal bacterial cell division
the structure of viruses only contains
those parts needed to invade and control a host cell
a virus can invade its host cell only
through making an exact fit with a specific host molecule
Synthesis: retroviruses
turn their RNA genome into DNA
viruses are (located)
ubiquitous in nature and have had major impact on development of biological life
viruses are ______________ in size, ranging from
ultramicroscopic in size, ranging from 20 nm up to 1000 nm in diameter
4. synthesis (replication and protein production)
under the control of viral genes, the cell synthesizes basic components of new viruses such as RNA molecule, capsomere, and spikes
archaeal viruses are
unique and not very understood
for many years, the cause of viral infections was
unknown
the length of the replication cycle
varies from 8 hours in polioviruses to 36 hours in herpesviruses
rabies infects
various cells of mammals
every bacterial species is parasitized by
various specific bacteriophages
General phases of the animal viral replication cycle EXCEPT: Adhesion Penetration Uncoating Synthesis Assembly Release
Adhesion (its adsorption)
provirus
viral DNA incorporated into the DNA of the host
Hepatitis D requires
viral particles from Hepatitis B to replicate
segmented RNA
individual genes exist on separate pieces of RNA (similar to human chromosomes)
prions are class of
infectious diseases called transmissible spongiform encephalopathies (TSEs)
This image shows what type of capsid -complex -naked -enveloped
naked
enveloped viruses can bud from
-cell membrane -nuclear envelope -endoplasmic reticulum
viruses lack
-enzymes for most metabolic processes -machinery for synthesizing proteins
Spikes can be found on ________ or ______ viruses
naked or enveloped viruses
filterable virus
-these early researchers found that when fluid from host organisms passed through porcelain filters designed to trap bacteria, the filtrate remained infectious -this proved that infection could be caused by fluid containing agents smaller than bacteria
Human prions diseases
1. Creutzfeldt-Jakob disease (CJD) 2. Variant Creutzfeldt Jakob Disease 3. Gerstmann Straussler scheinker syndrome 4. Fatal Familial Insomnia 5. Kuru
general phases of the animal viral replication cycle
1. absorption 2. penetration 3. uncoating 4. synthesis 5. assembly 6. release
events of lytic cycle of bacteriophages
1. adsorption 2. penetration 3. synthesis (duplication of phage components) 4. assembly of new virions 5. maturation 6. lyse of weakened cell
animal prion disease
1. bovine spongiform encephalopathy 2. chronic wasting disease 3. scrapie 4. transmissible mink encephalopathy 5. feline spongiform encephalopathy 6. exotic ungulate spongiform encephalopathy
virus structure contains
1. external coating (capsid) 2. core containing nucleic acid (DNA or RNA) 3. matrix proteins or enzymes (occasionally)
cell culture or tissue culture
1. grown in sterile chambers with special media that contain the nutrients for the cell to survive 2. cells for a monolayer or single confluent sheet of cells that supports viral multiplication 3. allows for the close inspection of culture for signs of infection
capsid (capsomere) two primary types
1. helical 2. icosahedral
the newer system of virus classification emphasize on (4 things)
1. host and diseases they cause 2. structure 3. chemical composition 4. similarities in genetic makeup
transformed cells
1. increased rate of growth 2. changes in their chromosome 3. changes in the cell's surface molecules 4. capacity to divide indefinitely
why are bird egg containing embryos used
1. intact self-supporting units 2. sterile environment 3. contain their own nourishment
primary purpose of viral cultivation
1. isolate and identify viruses in clinical specimens 2. prepare viruses for vaccines 3. do detailed research on viral structure, multiplication cycles, genetics, and effects on host cell
inherited forms of CJD include
Gerstmann Straussler Scheinker Syndrome Fatal Familial Insomnia
example of satellite viruses
Hepatitis D (delta virus)
Which is NOT a potential origin method of viruses Progressive Hypothesis Reductive Evolution Regressive Hypothesis Pre-life Hypothesis Virus First Escaped Gene Hypothesis All of these are correct
Pre-life hypothesis
early earth only contained
RNA
nucleic acid can be either
RNA or DNA, but not both
Which of the following is FALSE about viruses -They contain either RNA or DNA -They cannot infect algae -An example of a giant virus is mimivirus -Virus is latin for poison -Early researchers utilized a filtration experiment in which the filtered fluid remained infectious
They cannot infect algae
enveloped viruses take
a bit of cell membrane when they are released from the host cell
Dimitri Ivanoski and Martinus Beijerinck showed that
a disease in tobacco (plant virus) was caused by a virus
a carrier relationship between the cell and virus can last
a few weeks to the remainder of the host's life
regressive hypothesis: viruses adopted
a parasitic approach to replication
viroids are composed of
naked strands of RNA, lacking a capsid or any other coating
Viruses with a complex capsid infect what type of organism
bacteria
obligate intracellular parasites are found in
bacteria, protozoa, fungi, algae, plants, and animals
viruses that can infect bacteria are called
bacteriophages
examples of archaeal viruses
bottle shaped viruses spindle shaped viruses two tailed viruses whose tails "grow" once they are released from the infected cell
Clostridum botulinum acquire
botulinum toxin
satellite nucleic acid
cannot encode their own capsid protein
obligate intracellular parasites
cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses
what is the most prominent feature of viruses
capsid
what is always found in viruses
capsid and core nucleic acid
some cells maintain a __________ relationship, which means
carrier relationship, means the cell harbors the virus and is not immediately lysed
retroviruses
carry their own enzymes to convert RNA to DNA
what organism does Bovine Spongiform Encephalopathy affect
cattle
viruses bear no resembles to
cell and lack any of the protein synthesizing machinery found in cells
in vitro
cell or tissue culture methods
viruses infect
cells and influence their genetic material
having a larger genome allows
cells to carry out complex metabolic activity necessary for independent life
most common bird embryos used are
chicken duck turkey eggs
Vibrio cholera acquire
cholera toxin
vCJD has different
clinical and pathological characteristics from classic CJD
cell culture/ tissue culture: allows for the
close inspection of culture for signs of infection
3. uncoating
conditions within the endosome cause fusion of the vesicle membrane with the viral envelope, followed by release of the viral capsid and RNA into the cytoplasm
naked viruses
contain no outer layer just the capsid and nucleic acid core
direct fusion of the viral envelope with the host cell membrane
envelope merges directly with the cell membrane, liberating the nucleocapsid into the cell's interior
chronic wasting disease affects
deer, elk, reindeer, sika deer, and moose
Corynebacterium diphtheriae acquire
diphtheria toxin
spikes allow viruses to
dock (attach) with host cells
most bacteriophages contain
double stranded DNA, but some RNA types exist as well
RNA viruses can be
double stranded, but more often single stranded
nucleic acid can be __________ or ___________ stranded
double to single stranded
minority of patients develop CJD
due to inherited mutations in the prion protein gene
complex capsid are never
enveloped
virus is a genetic element that contains
either DNA or RNA surrounded by a protein capsid and that replicate only inside the cell
satellite viruses
encode their own capsid proteins
penetration by
endocytosis happens when an entire virus is engulfed by a cell and enclosed by a vesicle or vacuole
Synthesis: DNA viruses
enter the host cell's nucleus and are replicated and assembled there
Hepatitis D has the highest
fatality rate among all the hepatitis infections, at 20%
outside of the host, viruses lack most
features of life making them inactive or inert
enveloped viruses are more
flexible than capsid, which means they are more pleomorphic
old system for classification of viruses
for many years, animal viruses were classified on the basis of their host and the diseases they caused
spikes are projected
from the nucleocapsid or the envelope
some viruses carry
genes that directly cause cancer
virus
genetic element that can multiple only in a living (host) cell
escaped cell steps (progressive hypothesis)
genetic fragments escaped from cell developed protective coating reentered the cell to hijack machinery to reproduce
mobile genetic element
genetic material capable to moving within a genome
vCJD and CJD have unique
genetic profile of the prion protein gene
Hepatitis D is found
globally, but predominantly in Africa, Middle East, and Southern Italy
cases of Bovine Spongiform Encephalopathy in the UK
have dropped sharply (less than 14,000 in 1995 and 2 in 2015)
`viruses do show some traits of life, such as
hereditary, development, and evolution, but do not show these characteristics independent of their living host
examples of chronic latent state
herpes simplex (cold sores and genital herpes) and herpes zoster virus) and herpes zoster viruses (chicken pox and shingles)
molecules (spikes) on virus surfaces give them
high specificity for attachment to host cells
high specificity
highly specific for what the virus can infect
viruses need
host cells for energy, metabolic intermediates, and protein synthesis
there are no reported ______cases of chronic wasting disease
human, but it may pose a risk to nonhuman primates
how many genes in herpesvirus
hundreds of genes
viruses are constructed from
identical protein subunits called capsomere
capsomere
identical protein subunits that make up the capsid
Variant Creutzfeldt Jakob Disease first described
in 1996 in the United Kingdom
viroids are a significant pathogen
in economically important plants, such as tomatoes, potatoes, cucumbers, citrus trees
complex capsid only found
in viruses that infect bacteria
isolated animal cells are grown
in vitro in cell or tissue culture rather than in an animal or egg
lysogeny a condition
in which host chromosome carries bacteriophage DNA
outside of a host cell, viruses are
inactive
poliovirus infects
intestinal and nerve cells of primates
ocassional laboratory animals include
invertebrates (insects) and nonhuman primates
one of the main reasons viruses are generally considered nonliving
is that they are not cellular
until the discovery of prions
it was considered impossible that an agent lacking genetic material could be infectious and transmissible
spikes act like _____ and allow for ______
keys and allow for specificity
in vivo
laboratory bred animals and embryonic bird tissue
carrier relationships can remain
latent in the cytoplasm
Bovine Spongiform Encephalopathy has led to
laws in developing countries to ban the use of rendered ruminants proteins in ruminants feed as a precaution against the spread of prion infections in cattle and other ruminants
DNA viruses that are double stranded can be
linear or circular
Hepatitis B virus infects
liver cells of humans
viruses require
living cells as their medium
the silent virus infection
lysogeny
plaques manifest as
macroscopic, round, clear spaces that corresponds to areas of dead cells
oncoviruses
mammalian viruses capable of initiating tumors
what is occasionally found in the structure of virus
matrix proteins and enzymes
examples of provirus
measles and HIV
prions are
misfolded proteins, which transmit their misfolded shape onto variants of the same proteins
progressive hypothesis
mobile genetic elements (genetic material capable of moving within a genome) gain ability to exit one cell and enter another cell
cell culture/ tissue culture: cells form a
monolayer or single confluent sheet of cells that supports viral multiplication
T Even Bacteriophages
most widely studied phages mainly because they infect Escherichia Coli
complex capsid have
multiple types of proteins and take shapes that are not symmetrical
negative sense RNA
must be converted before translation can occur
nucleocapsid
nucleic acid + protein in enveloped viruses
viruses have their own
nucleic acid genome
detection of viral growth in culture
observation of degeneration and lysis of infected cells
when was the first infection of Bovine Spongiform Encephalopathy
occurred in the 1970s and was identified in 1986
satellites are grouped
on common characteristics
satellites depend
on other viruses for replication
cancer causing viruses
oncogenic
what is the smallest virus
parvoviruses which is 20 nm in diameter
the flexible cell membrane of the host is
penetrated by the whole virus or nucleic acid
chronic latent state
periodically becomes activated under the influence of various stimuli
some animal viruses enter their host cell and
permanently alter its genetic material and many times can cause cancer
satellites have no common
phylogeny and are grouped on common characteristics
virus is latin for
poison
Kuru: government discouraged the
practice of cannibalism, which led to a continuing decline in the disease, which has now mostly disappeared
prions are composed
primarily of proteins and contain no nucleic acid
induction
prophage in a lysogenic cell becomes activated and progresses directly into viral replication and the lytic cycle
virus basic structure consists of
protein shell (capsid) surrounding the nucleic acid core
capsid
protein shell that surround the genome of virus
prions stand for
proteinaceous infectious particles
other viruses produce______ that induce
proteins that induce a loss of growth regulation, leading to cancer
Louis Pasteur hypothesized that
rabies was caused by a "living thing" smaller than bacteria
viruses have immense potential for
rapid viral proliferation
positive sense RNA
ready for immediate translation
regressive hypothesis also known as
reduction evolution
Synthesis: RNA viruses
replicated and assembled in the cytoplasm
What component are viruses missing -DNA -Double-stranded DNA -RNA -Ribosomes
ribosomes
viruses do not contain
ribosomes
Kuru was a result of
ritualistic cannibalism
capsomere spontaneously
self-assemble into the finished capsid
DNA viruses can be
single stranded (ss) double stranded (linear or circular)
virus architecture is best observed with
special stains and electron microscopy
In most patients (85%) of CJD occur
sporadically
cell culture/ tissue culture: grown in
sterile chambers with special media that contains nutrients for the cell to survive
prions exact mode of infection is
still being investigated
satellites are
subviral particles
During which phase of the animal viral replication cycle do we see nucleic acid replication and protein production Adsorption Penetration Uncoating Synthesis Assembly Release
synthesis
viruses multiply by
taking control of the host cell's genetic material and regulating synthesis and assembly of new viruses
lysogeny contains the
temperate phage
occasionally, phage genes in
the bacterial chromosome can cause the production of toxins or enzymes that the bacterium would not otherwise have
transformation
the effect of oncogenic viruses on the cell
most biologist now agree that
the first replicating molecules consisted of RNA, and not DNA
In 1884, Louis Pasteur developed
the first vaccine for rabies
viruses posses only
the genes needed to invade host cells and redirect their activity
virion
the infectious virus particle; the viral genome surrounded by a protein and sometimes a outer layer
Host range
the limited range of cells that a virus can infect
the number of viral genes in a virus is_________ ________ compared
the number of viral genes in virus is quite small compared to that of a cell
release
the number of viruses released by infected cells is variable, controlled by the size of the virus and health of host cell
Hepatitis D worsens
the severity of liver damage
lysogeny
the silent virus infection
genome
the sum total of genetic material carried by an organism
1. absorption
the virus attaches to its host cell by specific binding of its spikes to cell receptors
2. penetration
the virus is engulfed by the cell membrane into a vesicle or endosome and transported internally
virus have shaped
the way cells, tissues, bacteria, plants, and animals have evolved
5. assembly
viral spike proteins are inserted into the cell membrane for the viral envelope; nucleocapsid is formed from RNA and capsomeres
infectious virus particle
virion
assembly
virus is put together using parts manufactured during the synthesis process
Viroids
virus like agent that parasitizes plants
prions are not
viruses
what is the most abundant entity on earth
viruses
how are bird embryos used in virus testing
viruses are injected through the eggshell by drilling a small hole or making a small window
viruses are _____ _____ that seize control
viruses are minute parasites that seize control of synthetic and genetic machinery of cells
viruses are ____ cells and their structure
viruses are not cells and their structure is very compact and economical
viruses do not _______________ fulfill the
viruses do not independently fulfill the characteristics of life
enveloped viruses
viruses have an outer layer consisting of phospholipid bilayer (from host cell membrane) and viral proteins
virus first
viruses may have existed in a precellular world as self-replicating units, those units then became more organized and more complex
plaques develop when
viruses released by an infected host cell radiates out into adjacent host cells and new cells become infected, die and release more viruses
bacteriophages
viruses that can infect bacteria
lysogenic conversion
when a bacterium acquires a new trait from its temperate phage
usual choices for laboratory animals
white mice rats hamsters guinea pigs rabbits