Chapter 13. Viruses, Viroids, and Prions
Match each gene type with the correct description
Proto-oncogene - stimulates cell growth Tumor suppressor gene - inhibits cell growth
Replicases are _____ polymerases
RNA-dependent RNA
HIV is described as a _____ because it uses reverse transcriptase to make a DNA copy from its RNA genome
Retrovirus
In ____ transduction, only bacterial genes adjacent to the prophase can be transferred; whereas in _______ transduction, any bacterial gene can be transferred
Specialized; generalized
In single strand (+) RNA viruses ______
The viral genome functions as mRNA and is translated
True or False: Normal prion proteins can have the same amino acid sequence as the abnormal form of the protein
True
True or false: Replication of a single stranded (-) RNA virus requires synthesis of a (+) RNA before new viral particles can be produced.
True
True or false: Tumor tissue can serve as a cell line for viral culture
True
True or false: Viruses can contain either DNA or RNA, but not both
True
This image shows the ____ stage of the lytic cycle of the T4 phage
assembly
This image shows the _____ stage of the M13 filamentous phage replication cycle
attachment
Identify all the methods by which an enveloped virus can gain entry into animal cells
b. fusion of the viral envelope and the cell membrane c. endocytosis of the virus by the host cell
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
Tumors are abnormal growths that result from a malfunction in the regulation of ______
cell growth
Multinucleated cells and inclusion bodies are examples of _____ effects
cytopathic
Which types of viruses are released by budding?
enveloped viruses
M13 particles are assembled during a process called ______, which the virus uses to exit the cell
extrusion
_______ phages cause productive infections that do not kill the host cell
filamentous
Replication of double-stranded DNA viruses _____
follows the central dogma of molecular biology
The molecules that viral spikes attach to on the host cell in order to gain entry are typically ______
glycoproteins
The _____ assay involves serially diluting viral samples, mixing each dilution with red blood cells, and determining the highest dilution that shows maximum clumping of the red blood cells
hemagglutination
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 host chromosome by _____ recombination
homologous
Following generalized transduction, DNA from the donor cell may be integrated into the recipient cell chromosome by ______ recombination
homologous
Protection of lysogens from infection by the same phage is called _____
immunity to superinfection
Through the process of phage ______, a prophage is excised and enters the lytic cycle
induction
The parameters illustrated in this figure best describe a(n) _____ infection
latent
_____ is a change in the phenotype of a lysogen as consequence of the specific prophage it carries
lysogenic conversion
Most animal DNA viruses replicate within the host cell's
nucleus
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
_____ assays are routinely used to quantify phage particles in environmental samples such as sewage
plaque
To maintain the lysogenic state, a _______ protein prevents expression of the gene required for excision
repressor
A virus acquired by inhalation would be called a(n)
respiratory virus
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
_____ phages have the option of entering the prophage state, while _____ phages always burst the host cell shortly after infection.
- Temperate - lytic
Which of the following processes are required for production of virus particles in a host cell?
- translation of viral genes - replication of viral genome - transcription of viral genes
Which of the following occur during the synthesis stage of the T4 lytic cycle?
-synthesis of phage proteins -Degradation of bacterial DNA -Synthesis of phage DNA
Which suffix represents a viral genus?
-virus
The replication strategies of animal viruses can be divided into three general categories: those used by _____ viruses, ______ viruses, and reverse transcribing viruses
DNA RNA
True or false: All virus infections can be clearly categorized as either acute or persistent
False
True or false: Most bacteria engulf bacteriophages as part of the phage replication strategy
False
Why are bacteriophages easier to study than animal viruses?
It is easier to grow the bacteriophage host cells in the lab
Rank the following by size, from smallest to largest, starting with the smallest at the top
1. Viruses 2. Bacteria 3. Human cells
The typical symptoms of cold sores can be caused by _______
- an initial infection with HSV-1 - latent HSV-1 that has reactivated
List the steps of an animal virus infection cycle in the correct order:
- attachment - penetration and uncoating - synthesis of viral proteins and replication of the genome - assembly - release
Enveloped viruses can derive their envelopes from ______
- certain host organelles - the host cytoplasmic membrane
The two categories or persistent infections are _____ and ______
- chronic - latent
Which of the following methods can be used to quantify animal viruses?
- quantal assay - plaque assay - hemagglutination - direct count
Regarding animal viruses, which of the following statements are true?
- some viruses require more than one host receptor for attachment - 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
In the case of retroviruses, reverse transcriptase use 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
In a(n) _____ viral titer can be determined by counting clear zones in a monolayer of cells
plaque assay
The phospholipid bilayer found surrounding the capsid of some viruses is the _____.
envelope
Some pathogenic bacteria produce toxins that are encoded on prophage DNA, and these are examples of ______ conversion
lysogenic
Which of the following are the three general shapes of most viruses?
- helical - complex - icosahedral
Which of the following about classifying viruses is FALSE?
It is not as important as classifying organisms since they are not living entities
True or false: Viral particles can be shed from a host in feces, urine, genital secretions, blood, or mucus and saliva released from the respiratory tract during coughing or sneezing, allowing for transmission to a new host.
True
What are the two types of transduction?
generalized and specialized
______ transduction is the result of excision errors made as temperate phages transition from a lysogenic to a lytic cycle
specialized
After a virus enters a cell, the nucleic acid separates from the protein coat, a process called ____
uncoating
Which of the following cycles ends with the death (lysis) of the bacterial host cell?
Lytic
Infections that have a sudden onset of symptoms of relatively short duration are described as _____ infections
acute
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 persistant
Enveloped viruses exit host cells by _____; non-enveloped viruses are released upon ____ of the host cell
budding, apoptosis
The number of phage particles released from a host cell is called the _____ size
burst
Animal viruses ________
can only be grown in animal cells
The concentration of infectious phage particles in a sample is called the ________
titer
Phage heads that contain only bacterial DNA are called generalized _____ particles
transducing
Match the genome of each type of RNA virus with its description of function
(+) strand genome - serves as mRNA (-) strand genome - Is the complement to mRNA double-stranded genome - Consists of both a(+) and (-) strand
In double-stranded RNA viruses, the viral replicase uses the ___ strand of RNA to make ___ strands of RNA that can then be translated
(-) then (+)
Which of the following are diseases caused by prions?
- Creutzfeldt-Jakob disease - Bovine spongiform encephalopathy - Scrapie
Which of the following statements about prions are true?
- Infectious prion proteins are insoluble and aggregate in brain tissue - Infectious prion proteins can convert normal prion proteins into an abnormal form - Infectious prion proteins have a different shape from normal prion proteins
Match each tumor type to the correct statement
- Malignant - spreads to nearby tissue - Benign - does no spread to nearby tissue (fatty tissue)
True or False: Lysogen are more susceptible to reinfection by the same type of phage
False
True or false: Viroids contain a capsid but lack an envelope
False
True or false: When a bacterial culture is infected with a temperate phage, all particles of the phage will lysogenize their host
False
During the ______ or maturation step in viral multiplication, capsids and genetic material are packaged into virions.
assembly
This image shows the _____ stage of the T4 phage lytic cycle
attachment - where the little bodies are crawling on the cell
A viral capsid is made up of subunits called _______
capsomeres
Tumors are abnormal growths that result from a malfunction in the regulation of _____________.
cell growth
The hepatitis B virus sometimes causes an infection that results in a continuous and low-level production of virus particles. This type of infection pattern is specifically described as a(n) _____ viral infection
chronic
If viruses are present in high enough concentrations in a sample, they can be quantified directly using a(n) ______ microscope
electron
RNA viruses have a higher mutation rate than DNA viruses because replicase lacks ______ ability
proofreading
A _____ is an animal virus genome residing silently in a host cell genome
provirus
An enzyme that uses an RNA molecule as a template to make a complementary copy of DNA is called _______
reverse transcriptase
Which are the two major categories of viral infections?
- Persistent - Acute
The physical rupture of a cell is termed
- lysis
Replication of temperate phages and lytic phages have which steps in common?
-Assembly -Attachment -Release -Biosynthesis of viral components -Genome entry
Circular clearings in a bacterial lawn, caused by phage-induced lysis, are called ________
plaques
In this image of a lawn of bacteria infected by a phage, the small, circular clearings are called _____
plaques
Match each possible outcome of phage replication with the correct definition?
- Productive infection - New viral particles are produced - 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?
- Spikes - Tail fibers
Which of the following are cytopathic effects of viruses?
- Synctia - Inclusion bodies
When cultivated in flasks, human cells from solid tissues _______
- adhere to the bottom of the surface - grow as a monolayer
Methods for cultivating animal viruses include _____
- embryonated chicken eggs - tissue culture
A non-enveloped virus can gain entry into animal cells via _____
- endocytosis of the virus by the host cell
Animal viruses can be studied by infecting _____
- fertilized chicken eggs - cell or tissue culture - live animals
Which are the two main criteria used in classifying viruses?
- genome structure - host range
In RNA viruses that have a single strand (+) RNA genome, the viral genome _____.
- is used as a template to make complementary (-) RNA strands that act as templates to produce more (+) RNA strands - can be translated to make proteins
At a minimum, all viruses are composed of ______.
- nucleic acids - proteins
Which of the following are non-cellular infectious agents?
- prions - viroids - viruses
Some viruses cause an infected cell to form a distinct region called an ______ body, which is the site of viral replication
inclusion
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 ploymerase
