Which of the following statements describes a generalist virus?
answer
It infects many kinds of cells in many different hosts.
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All of these are steps in the lytic cycle of a temperate bacteriophage. Which happens second?
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entry
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Which of the following is NOT represented in viral classification schemes?
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class
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Which of the following diseases is NOT caused by prions?
answer
Chagas' disease
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Lysozyme is important for which of the following stages of lytic replication in bacteriophage T4?
answer
entry and release
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Conventional genetic analyses of prions involving rRNA sequences are impossible because __________.
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they do not contain nucleic acids
Prions do not contain nucleic acids, so conventional genetic analyses involving molecules such as rRNA are not applicable.
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The envelope found in some virus particles differs from the cytoplasmic membrane of cells in that __________.
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it does not perform the physiological functions carried out by the cytoplasmic membrane
Because viruses are not cells, their envelopes do not carry out the physiological functions of a cytoplasmic membrane, such as endocytosis or active transport.
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Which of the following is an essential component of all viruses?
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capsid
All viruses have a capsid surrounding their nucleic acid.
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Lysogeny is associated with all of the following EXCEPT __________.
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animal viruses
Animal viruses do not undergo lysogeny.
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Put the following viral structures in order, from simplest to most complex:
answer
capsomere
capsid
nucleocapsid
virion
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Viruses can be grown in all of the following EXCEPT __________.
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sterile nutrient agar
Viruses cannot be grown in sterile nutrient agar or other microbiological media because viruses must have a host cell present to reproduce.
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You have isolated bacterium that contains a prophage. Which of the following is true concerning the prophage?
answer
The phage is in the lysogenic cycle.
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In a plaque assay, a microbiologist counts 20 plaques on a plate. How many plaque-forming units can be assumed to have been present in the original bacterium-virus mixture on the plate, if there was no dilution of the mixture prior to plating?
answer
20
question
Which of the following would be an appropriate mode of action for a new anticancer drug?
answer
inactivation of an oncogene
Either the activation of tumor repressor genes or the inactivation of oncogenes would be an appropriate mode of action for a new anticancer drug.
question
Which of the following types of enzymes is necessary for the replication of most double-stranded DNA (dsDNA) viruses?
answer
cellular DNA polymerase
Most dsDNA viruses do not require any kind of special enzyme for their replication because they are able to utilize the normal enzymes and processes of the host cell.
question
The infectious cycles of enveloped animal viruses and temperate bacteriophages are most similar because __________.
answer
the infected cell may live for a long time
Because enveloped viruses are shed slowly and persistently from the host cell by budding, the host cell may survive for a long time.
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Most viral genomes are much smaller than the genomes of the cells they infect. Which of the following CANNOT be inferred from this statement?
answer
Most viruses can infect only certain types of cells.
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Which of the following is NOT a way in which viruses differ from all other living things?
answer
They live inside host cells.
Other organisms, including some bacteria and protozoans, live inside the cells of their hosts.
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A phage T4 particle that has lost its tail fibers will have a replication cycle that is blocked at which of the following stages?
answer
attachment
A phage T4 particle with no tail fibers would be blocked at the attachment stage, the initial stage of its replication cycle.
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Both viruses and carcinogenic chemicals can cause tumors by __________.
answer
disruption of cell division
Viruses and carcinogenic chemicals both cause tumors by interfering with the normal cellular controls over division and growth.
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Contact between a phage and its bacterial host occurs by _____.
answer
a random collision
Phages are incapable of movement, and thus are completely reliant on randomly colliding with a bacterium before attachment.
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What portion of bacteriophage T4 enters E. coli?
answer
Only the T4 genome enters the bacterial cell.
The capsid remains on the surface of the cell, and the genome is the only portion to enter the cell.
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Once entry into the bacterial cell has been achieved, the next step in a lytic replication cycle is _____.
answer
synthesis
Once the phage has entered a cell, viral protein synthesis begins.
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During a lytic replication cycle, what action does a phage take to ensure that its host bacterium does NOT continue synthesizing cellular molecules?
answer
Phage enzymes degrade the bacterial DNA.
By degrading the host DNA, the phage ensures that only phage proteins are synthesized.
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In a lytic cycle of replication, release of phages involves _____.
answer
the bacterial cell bursting open
The bacterial cell undergoes lysis, meaning that it is destroyed. Phages are then released.
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A major difference between the lytic and lysogenic cycles of phage replication is that during the lysogenic phase _____.
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the phage genome inserts itself into the host genome
The phage DNA is integrated into the host DNA without destroying the cell.
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What factor may induce a prophage to enter the lytic cycle?
answer
UV light
Ultraviolet radiation is known to cause the induction of prophage into the lytic cycle.
question
During the lysogenic cycle, it is possible for integrated phage genes to change the characteristics of the host cell. This is known as _____.
answer
lysogenic conversion
Lysogenic conversion involves phenotypic changes to the bacterium due to new genes from the integration of the phage genome.
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How are viruses different from cells?
answer
They require a host in order to reproduce.
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What is the function of the structural elements of a virus?
answer
To package and protect the viral genome
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Lysogenic viral DNA integrating into the host genome is referred to as
answer
a prophage.
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Which of the following events might trigger induction of a temperate bacteriophage?
answer
Exposure to UV light
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How is the lytic cycle different from the lysogenic cycle with respect to the infected host cell?
answer
The host cell dies during the lytic stage.
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What is the fate of the prophage during the lysogenic stage?
answer
It is copied every time the host DNA replicates.
question
We sometimes are able to generate antibodies (immune system proteins) that bind to and cover up some of the proteins on the outermost portion of a virus while it is in the bloodstream. This renders the virus unable to reproduce. Which step of viral replication are antibodies directly preventing?
answer
attachment
question
Enveloped viruses have a layer of lipids surrounding their capsid. This envelope is made mostly of host cell membrane. In which step does the virus acquire this envelope?
answer
release
During budding release, the virus "steals" some of the host membrane to use for itself.
question
What occurs during viral uncoating?
answer
The capsid breaks apart, releasing the viral genome.
question
The normal function of the PrP protein in mammals is believed to be:
answer
assisting in normal synaptic development and function.
question
How do normal prion proteins (PrP) differ from the infectious prion proteins?
answer
Normal PrP have alpha-helices; infectious PrP have beta-pleated sheets.
question
How does the number of infectious prions increase?
answer
Prions transform normal proteins into the misfolded beta-pleated sheet configuration; therefore, prions multiply by conversion.
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Why are the beta-pleated multimers of PrP potentially pathogenic?
answer
The multimers are more stable and resistant to protease.
question
From which phrase is the term "prions" derived?
answer
Proteinaceous infectious particles
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In what year did Stanley Prusiner discover prions?
answer
1982
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Which disease did Stanley Prusiner first identify as being caused by prions?
answer
Scrapie
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How are prions different from other infectious agents?
answer
They lack nucleic acid.
question
In the cell, mRNA is produced during the process of __________ and utilized during the process of __________.
answer
transcription; translation
question
Viruses lack a
answer
cytoplasmic membrane
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A clear zone of phage infection in a bacterial lawn is __________.
answer
a plaque
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Which of the following viruses can be latent?
answer
HIV, chicken pox, herpes viruses
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A naked virus __________.
answer
has no membraneous envelope
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The enzyme reverse transcriptase functions by making a(n) __________ copy of a(n) __________ molecule.
answer
DNA; RNA
question
Another name for a complete virus is __________.
answer
virion
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Lysozyme, an enzyme used by some viruses to attack the peptidoglycan in a bacterial cell, affects which of the following structures?
answer
Cell wall
question
Which of the following scientists was the first to demonstrate that viruses are acellular?
answer
Ivanowski
question
A virus that is specific for a bacterial host is called a __________.
answer
phage
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Which of the following is not an acellular agent?
answer
Rickettsia
question
DNA polymerase is necessary for which of the following processes?
answer
DNA replication
question
Ribosomes are responsible for the production of which of the following molecules?
answer
Polypeptides
question
Viruses, viroids, and prions are
answer
acellular disease-causing agents that clack cell structure and cannot metabolize, grown, self-reproduce, or respond to their environment
question
A virus is a tiny
answer
infectious agent with nucleic acid surrounded by proteinaceous capsomeres that form a coat called capsid.
question
A virus exists in an
answer
extracellular state and an intracellular state.
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