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