Chapter 13: Viruses, Viroids, and Prions
multinucleated cells and inclusion bodies are examples of ______ effects
cytopathic
benign
does not spread to nearby tissue
viral genomes can be
either single-stranded or double-stranded
animal viruses that do not have an envelope can only enter their host cell by ______
endocytosis
which type of viruses are released by budding?
enveloped viruses
true or false: all non-cellular infectious agents are viruses
false
true or false: lysogens are more susceptible to reinfection by the same type of phage
false
replication of double-stranded DNA viruses
follows the central dogma of molecular biology
______ transduction is the result of packaging errors during the assembly stage of phage replication
generalized
the molecule that viral spikes attach to on the host cell in order to gain entry are typically ______
glycoproteins
temperate phages are more likely to enter the lysogenic cycle when bacterial cells are ______
growing slowly
viruses that appear cylindrical are called ______
helical
in a(n) ______ assay, the clumping of red blood cells is used to determine viral titer
hemagglutination
(-) strand genome
is the complement to mRNA
why are bacteriophages easier to study than animal viruses?
it is easier to grow the bacteriophages host cells in the lab
in a quantal assay, LD^50 is the amount of pathogen that ______
kills half of a test population
which of the following infections are analogous to lysogenic infections by the bacteriophages in that they involve a viral genome that is silent in the host cell?
latent
which of the following describes a consequence of lysogeny that could result in human disease?
lysogenic conversion
in enveloped viruses, sandwiched between the nucleocapsid and the envelope is the ______
matrix protein
productive infection
new viral particles are produced
lysogens are protected against infection by the same phage because the phage-encoded repressor protein binds to the ______ on the incoming phage, preventing expression of the phage genes
operator
______ infections remain for years, or even the lifetime of the host, sometimes without any symptoms
persistent
after a virus enters a cell, the nucleic acid separates from the protein coat, a process called
uncoating
latent state
viral genome remains silent within the cell
which of the following are viral protein components that attach to specific receptors on host cells?
- tail fibers - spikes
the typical route of infection for mad cow disease is via ______
consumption of contaminated food
true or false: it is easier to cultivate animal viruses than bacteriophages
false
how does bacteriophage nucleic acid enter the host cell?
injection
lysogeny is best described as
integration of the viral genome into the host chromosome
the physical rupture of a cell is termed
lysis
some pathogenic bacteria produce toxins that are encoded on prophage DNA, and these are examples of ____ conversion
lysogenic
virus infections that result in the formation of new virus particles are described as
productive
a ______ is an animal virus genome residing silently in a host cell genome
provirus
methods for cultivating animal viruses include ______
- tissue culture - embryonated chicken eggs
this image shows the ______ stage of the M13 filamentous phage replication cycle
attachment
true or false: viroids contain a capsid but lack an envelope
false
true or false: viral particles can be shed from a host in feces, urine, genital secreations, blood, or mucus and saliva released from the respiratory tract during coughing or sneezing, allowing for transmission to a new host
true
true or false: viruses can contain either DNA or RNA, but not both
true
a abnormal growth of tissue resulting from a malfunction in the normally highly regulated process of cell growth is a ______
tumor
because of their ability to multiple indefinitely in vitro, established cells are made up of ______ cells
tumor
true or false: enveloped and non-enveloped viruses all mature in the cytoplasm of the host cell
false
true or false: there is no need to classify viruses because they are not living organisms
false
true or false: when a bacterial culture is infected with a temperate phage, all particles of the phage will lysogenize their host
false
______ phages cause productive infections that do not kill the host cell
filamentous
most animal DNA viruses replicate within the host cells ______
nucleus
the concentration of infectious phage particles in a sample is called the ______
titer
which of the following are sources of plant viruses?
- contaminated seeds - soil - insects - contaminated pollen
M13 particles are assembled during a process called ______, which the virus uses to exit the cell
extrusion
true or false: normal prion proteins can have the same amino acid sequence as the abnormal form of the protein
true
true or false: double-stranded RNA viruses carry their own replicase because the host cell cannot translate double-stranded RNA
true
true or false: replication of a single stranded (-) RNA virus requires synthesis of a (+) RNA before new viral particles can be produced
true
before enveloped viruses bud from a host cell, specific viral proteins insert into the host membrane. these proteins become ______
viral spikes
signs of viral infection in plants include ______
- yellowing of leaves - stunted growth - presence of tumors
the replication strategy of viruses can be divided into three general categories: those used by ______
- DNA viruses - RNA viruses - reverse transcribing
which of the following statements about viruses are true?
- viruses contain RNA or DNA but not both - the viral capsid is composed of protein
the major categories of animal viral infections are ______ infections, characterized by the sudden onset of symptoms of a relatively short duration, and ______ infections that can continue with or without symptoms for years
- acute - persistent
viruses that infect bacteria are called ______
- bacteriophages - phages
which of the following are non-cellular infectious agents?
- viroids - viruses - prions
which facts best support the position that viruses are not living organisms?
- viruses cannot reproduce on their own - viruses are inert outside of a host
late proteins of the T4 lytic cycle include
-T4 capsomere components -T4 tail fibers
which suffix represents a viral genus?
-virus
list the steps of an animal virus infection cycle in the correct order
1. attachment 2. penetration and uncoating 3. synthesis of viral proteins and replication of the genome 4. assembly 5. release
rank the following by size, from smallest to largest, starting with the smallest at the top
1. viruses 2. bacteria 3. human cells
infections that have a sudden onset of symptoms of relatively short duration are described as ______ infections
acute
the accumulation of mutations in genes that encode viral surface proteins recognized by the immune system results in a type of antigenic variation called ______
antigenic drift
animal viruses ______
can only be frown in animal cells
viroids____
cause serious plant disease
although live animals and fertilized chicken eggs have been used to cultivate animal viruses in the past, these have now been largely replaced by ______ culture
cell
which type of viral infection is characterized by the continuous, low-level production of new virus particles by animal host cells?
chronic
double-stranded genome
consist of both a (+) and (-) strand
during specialized transduction, DNA from another bacterial cell may be integrated into the recipient cell chromosome by ______ recombination
homologous
following generalized transduction, DNA from the donor cell may be integrated into the recipient cell chromosome by ______ recombination
homologous
at least 15 ______ are associated with the development of cancers. A vaccine that protects against the stereotypes most highly associated with cervical cancers and some other cancers is available
human papillomaviruses
some viruses cause an infected cell to form a distinct region called an ______ body, which is the site of viral replication
inclusion
through the process of phage ______, a prophage is excised and enters the lytic cycle
induction
in quantal assays, the ID^50 is the amount of pathogen that ______
infects half of the test population
unlike animal viruses that attach to specific receptors in order to gain entry into the cell, ______ viruses can gain entry into a cell through damage in the cell wall
plant
the circular clearings in this image of a bacterial lawn are called ______
plaques
______ are the causative agents of transmissible spongiform encephalopathies
prions
(+) strand genome
serves as mRNA
reassortment of gene segments that encode viral surface proteins that are recognized by the immune system can result in a loss of the immune system's ability to recognize and respond to the virus. This phenomenon is called antigenic ______
shift
______ transduction is the result of excision errors made as a temperate phages transition from a lysogenic to a lytic cycle
specialized
malignant
spreads to nearby tissue
Proto-oncogene
stimulates cell growth
the enteric viruses are a group of taxonomically unrelated viruses that are grouped together for which of the following reasons?
they are transmitted by the fecal-oral route
a single virus particle is referred to as a ______
virion
a ______ is an infectious agent that lacks a capsid and consist only of RNA
viroid
a ______ is an infectious agent that lacks a capsid and consists of only RNA
viroid
which of the following are non-cellular infectious agents composed of only a single-stranded RNA molecule?
viroids
which of the following statements about prion replication is true?
PrP^SC interacts with PrP^C, converting it to PrP^SC
reverse transcriptase is a(n) ______ polymerase
RNA- dependent DNA
replicates are ______ polymerases
RNA-dependent RNA
replication of single-stranded DNA viruses is quite similar to that of double stranded DNA viruses, except that ______
a component to the single-stranded DNA molecule must be synthesized
the ______ or maturation stage of the T4 phage lytic cycle is marked by the formation of new phage particles inside of the host cell
assembly
this image shows the ___ stage of the lytic cycle of the T4 phage
assembly
which of the following describes the various parts coming together to produce virions?
assembly
the binding of a bacteriophage surface protein to a host cell receptor is called
attachment
viral infections in plants can cause diseases ______
that are economically devastating
the number of phage particles released from a host cell is called the _____ size
burst
which of the follwing statements about virus nucleic acid is true?
viruses contain with DNA or RNA
if viruses are present in high enough concentrations in a sample, they can be quantified directly using a(n) ______ microscope
electron
true or false: all virus infections can be clearly categorized as either acute or persistent
false
HIV infection ______
has features of both acute and persistent infections
the most important transmitters of plant viruses are probably ______
insects
a viral infection in which the viral genome is integrated into an animal host cell chromosome, yet can reactivate to cause a productive infection, is categorized as a(n) ______ infection
latent
because they are dependent on host cells, viruses are classified as ______
obligate intracellular parasites
to maintain the lysogenic state, a ____ protein prevents expression of the gene required for excision
repressor
DNA viruses often encode their own ______ for DNA synthesis and gene expression, which allows them to replicate even if the host cell is not actively duplicating its own chromosome
DNA polymerase
a problem encountered in primary cultures derived from normal tissue cells is that cells will ______
only divide a limited number of times
viruses that have an RNA genome and use reverse transcriptase to synthesize a DNA copy of that genome are called ______
retroviruses
an enzyme that uses an RNA molecule as a template to make a complementary copy of DNA is called ______
reverse transcriptase
the study of viruses is important because ______
- bacteriophages play a significant ecological role in reducing bacterial populations of nature - viruses can be a vehicle for horizontal gene transfer in bacteria - there are many medically important viruses that cause disease
regarding animal viruses, which of the following statements are true?
- blocking a host receptor with a drug would prevent a virus from infecting that cell - viruses use their spikes to attach to host cell receptors - some viruses require more than one host receptor for attachment
which of the following are diseases caused by prions?
- bovine spongiform encephalopathy - creutzfeldt-jakob disease - scrapie
what mechanisms do newly assembled viruses use to leave their host cell?
- budding - triggering apoptosis
in RNA viruses that have a single strand (+) RNA genome, the viral genome ______
- can be translated to make proteins - is used as a template to make complementary (-) RNA strands that act as templates to produce more (+) RNA strands
enveloped viruses can derive their envelopes from ______
- certain host organelles - the host cytoplasmic membrane
identify all the methods by which enveloped virus can gain entry into animal cells
- fusion of the viral envelope and the cell membrane - endocytosis of the virus by the host cell
what are the two types of transduction?
- generalized - specialized
replication of temperate phages and lytic phages have which steps in common?
- genome entry - biosynthesis of viral components - release - assembly - attachment
which are the two main criteria used in classifying viruses?
- genome structure - host range
which of the following methods can be used to quantify animal viruses?
- hemagglutination - plaque assay - quantal assay - direct count
the typical symptoms of cold sores can be caused by ______
- latent HSV-1 that has reactivated - an initial infection with HSV-1
in double-stranded RNA viruses, the viral replicase uses the ______ strand of RNA to make ______ strands of RNA that can then be translated
- negative - positive
which of the following processes are required for the production of virus particles in a host cell?
- replication of viral genome - transcription of viral genes - translation of viral genes
in ______ transduction, only bacterial genes adjacent to the prophage can be transferred; whereas in ______ transduction, any bacterial gene can be transferred
- specialized - generalized
in the case of retroviruses, reverse transcriptase uses a viral RNA template to synthesize DNA, which can then be ______
- transcribed and translated to form new virions - integrated into a host cell chromosome where it remains latent
