TEST BANK BROCK BIOLOGY OF MICROORGANISMS 13TH EDITION MADIGAN
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
Viral replication is
1)
_______
A)
independent of both the cell’s chromosomes and the cell itself (although the cell does provide a convenient matrix for replication).
B)
dependent on the cell’s chromosomes but independent of the cell itself.
C)
independent of the cell’s chromosomes but dependent on the cell itself.
D)
dependent on both the cell’s chromosomes and the cell itself.
2)
Viral replication occurs
2)
_______
A)
extracellularly.
B)
intracellularly.
C)
both intracellularly and extracellularly.
D)
either intracellularly or extracellularly, depending on the virus involved.
3)
Viral size is generally measured in
3)
_______
A)
centimeters.
B)
picometers.
C)
nanometers.
D)
micrometers.
4)
Enveloped viral membranes are generally ________ with associated virus-specific ________.
4)
_______
A)
lipid bilayers / glycoproteins
B)
lipid bilayers / phospholipids
C)
glycolipid bilayers / phospholipids
D)
protein bilayers / lipids
5)
Which statement is TRUE?
5)
_______
A)
Many viruses contain their own nucleic acid polymerases.
B)
All viruses contain their own nucleic acid polymerases.
C)
The origins of the nucleic acid polymerases used by viruses are eukaryotic.
D)
Viruses do not contain their own nucleic acid polymerases.
6)
Reverse transcriptase is a(n)
6)
_______
A)
DNA-dependent DNA polymerase.
B)
RNA-dependent RNA polymerase.
C)
DNA-dependent RNA polymerase.
D)
RNA-dependent DNA polymerase.
7)
Viruses infecting ________ are typically the easiest to grow in the laboratory.
7)
_______
A)
prokaryotes
B)
fungi
C)
animals
D)
plants
8)
All viral particles
8)
_______
A)
exhibit cell lysis under a particular condition.
B)
are metabolically inert.
C)
contain an envelope to prevent its degradation outside of a host.
D)
are smaller than bacterial cells.
9)
Cellular receptors may be composed of
9)
_______
A)
lipids.
B)
proteins.
C)
carbohydrates.
D)
combinations of any or all of the above.
10)
Restriction is
10)
______
A)
the viral process whereby a host’s DNA ceases normal functioning.
B)
the viral process whereby the virus prevents other viruses from entering the cell.
C)
a general host mechanism to prevent virus particles from further infective action.
D)
a general host mechanism to prevent the invasion of foreign nucleic acid.
11)
The Nobel Prize laureate David Baltimore is credited with the discovery of
11)
______
A)
retroviruses and reverse transcriptase.
B)
parvoviruses.
C)
T-series viruses (such as T2, T4, etc.).
D)
prions.
12)
The simplest form of viral reproduction in RNA viruses is that which occurs with the
12)
______
A)
negative-strand DNA viruses.
B)
positive-strand RNA viruses.
C)
negative-strand RNA viruses.
D)
positive-strand DNA viruses.
13)
Bacteriophages’ genomes are typically composed of
13)
______
A)
double-stranded RNA.
B)
single-stranded RNA.
C)
double-stranded DNA.
D)
single-stranded DNA.
14)
A virus that kills its host is said to be
14)
______
A)
virulent or lysogenic, but not temperate.
B)
lysogenic.
C)
temperate.
D)
lytic or virulent.
15)
Which T bacteriophage has been studied most extensively?
15)
______
A)
T7
B)
T2
C)
T4
D)
T6
16)
The packaging mechanism of T4 DNA involves cutting of DNA from
16)
______
A)
DNA concatemers.
B)
circular genetic elements.
C)
linear genetic elements.
D)
none of these; they are all transcribed directly from inserted viral DNA.
17)
A prophage replicates
17)
______
A)
along with its host while the lytic genes are expressed.
B)
independently of its host while the lytic genes are not expressed.
C)
along with its host while the lytic genes are not expressed.
D)
independently of its host while the lytic genes are expressed.
18)
The virus repressor protein
18)
______
A)
has different actions in different situations.
B)
does not control the prophage’s lytic genes but does control the incoming genomes of the same virus.
C)
controls both the lytic genes on the prophage and prevents an incoming virus of the same type.
D)
controls the prophage’s lytic genes but not the incoming genomes of the same virus.
19)
Lambda is
19)
______
A)
a temperate phage that infects Escherichia coli.
B)
replicated by the rolling circle mechanism.
C)
a linear double-stranded DNA phage.
D)
all of the above.
20)
Retroviruses
20)
______
A)
may cause cancer.
B)
transcribe DNA from RNA template.
C)
include the virus that causes AIDS.
D)
do all of the above.
21)
The primer for retrovirus reverse transcription is a specific
21)
______
A)
nuclear tDNA.
B)
nuclear tRNA.
C)
tRNA encoded by the cell.
D)
tRNA encoded by the virus.
22)
An integrated stable genetic element in a eukaryotic cell
22)
______
A)
is analogous to the integration of phage DNA into a bacterial genome.
B)
can occur anywhere in the cellular DNA.
C)
is called a provirus.
D)
is all of the above.
23)
A viroid
23)
______
A)
lacks a capsid.
B)
lacks protein-encoding genes.
C)
is a small, circular ssRNA molecule.
D)
is characterized by all of the above.
24)
When packaged in the virion, the complete complex of nucleic acid and protein is known as the virus
24)
______
A)
concatemer.
B)
envelope.
C)
nucleocapsid.
D)
capsid.
25)
Which of the following are the hosts for most enveloped viruses?
25)
______
A)
fungi
B)
Archaea
C)
animals
D)
Bacteria
26)
Plant viruses can be difficult to work with because
26)
______
A)
their study sometimes requires the use of the whole plant.
B)
plant viruses often require a break in the plant cell wall to initiate infection.
C)
plants typically grow much slower than bacteria.
D)
All of the above are factors.
27)
What genome composition makes viruses most susceptible to destruction by prokaryotic restriction endonucleases?
27)
______
A)
ssRNA
B)
dsDNA
C)
ssDNA
D)
dsRNA
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
28)
Viruses can confer additional properties on their host cells, which can in turn be inherited.
28)
______
29)
Viruses have both an intracellular and an extracellular form.
29)
______
30)
Viruses can redirect host metabolic functions.
30)
______
31)
Currently there is no formal system of viral taxonomy, although several systems are presently being developed.
31)
______
32)
There is at least one known virus whose genome is actually larger than a cellular genome.
32)
______
33)
Some viruses possess icosahedral heads and helical tails.
33)
______
34)
In the first few minutes after host cell infection, the virus undergoes an eclipse.
34)
______
35)
Penetration requires that the entire virus is inserted within the host.
35)
______
36)
RNA viruses encode host restriction systems designed to destroy host DNA.
36)
______
37)
Tailed bacterial viruses can be used as genetic engineering tools.
37)
______
38)
Although T4 encodes over 250 proteins, it does not encode its own RNA polymerase.
38)
______
39)
Temperate viruses can enter into either a lytic or lysogenic cycle.
39)
______
40)
Lysogeny is unique to bacteriophages; similar relationships have not been found among the animal viruses.
40)
______
41)
A temperate virus does not exist as a virus particle inside the host cell.
41)
______
42)
The virus repressor protein provides immunity to infection by the same type of virus.
42)
______
43)
A lytic infection results in death of the host cell.
43)
______
44)
An RNA genome itself serves as mRNA in negative-stranded RNA viruses.
44)
______
45)
Patrick Forterre’s hypothesis states that an RNA virus infected a cell to form the last universal common ancestor (LUCA).
45)
______
46)
DNA viruses, along with cells in Archaea, Bacteria, and Eukarya, all follow the central dogma of molecular biology.
46)
______
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
47)
When a virus enters a host cell in which it can replicate, the process is called a(n) ________.
47)
_____________
48)
The term “phage” is generally reserved for the viruses that infect ________.
48)
_____________
49)
Rod-shaped viruses have ________ symmetry, and spherical viruses have ________ symmetry.
49)
_____________
50)
The Baltimore Classification System groups seven viral classes according to ________ and ________.
50)
_____________
51)
Regarding the viral membrane in an enveloped virus, the lipids are derived from the ________, and the proteins are encoded by ________.
51)
_____________
52)
Virions infecting some bacteria possess the enzyme ________ that makes a small hole in the bacterial cell wall, allowing the viral nucleic acid to enter.
52)
_____________
53)
The use of ________ has greatly enhanced research on most animal and many plant viruses.
53)
_____________
54)
The smallest unit that causes a detectable effect when added to a susceptible host is known as a(n) ________.
54)
_____________
55)
A clearing of no host cells among a lawn of growing host cells is known as a(n) ________, which in principle represents ________.
55)
_____________
56)
Two chemical modifications of viral DNA that work to avoid host restriction mechanisms are ________ and ________.
56)
_____________
57)
The process of copying information found in RNA into DNA is called ________.
57)
_____________
58)
Bacteriophage Lambda integrates into an E. coli genome by the action of ________.
58)
_____________
59)
Viral proteins are categorized as early and late. Early proteins are ________, while late proteins include ________.
59)
_____________
60)
A cell that allows the complete replication cycle of a virus to take place is said to be a(n) ________.
60)
_____________
61)
A cell infected with T4 phage undergoes cell lysis because the virus codes for ________, which acts by ________.
61)
_____________
62)
Lambda and other temperate viruses have an exceedingly complex genetic switch that ________.
62)
_____________
63)
The two events necessary to establish lysogeny for lambda phage are ________ and ________.
63)
_____________
64)
Whether lambda phage undergoes the lytic or lysogenic cycle is dependent on the presence or absence of ________.
64)
_____________
65)
T4 bacteriophage contains 5-hydroxymethylcytosine that replaces ________ and is a protectant against ________.
65)
_____________
66)
Present in both animals and plants, ________ are incomplete and therefore require the presence of other active helper viruses.
66)
_____________
67)
Animal viruses are more easily lysed compared to prokaryotic cells, because animal host cells ________.
67)
_____________
68)
In viruses, genetic information flows from ________ to ________.
68)
_____________
69)
The number of infectious plaque forming units (pfu) per volume of fluid is known as the ________.
69)
_____________
70)
Transmissible spongiform encephalopathies (TSEs) are caused by ________.
70)
_____________
71)
Avirulent prions consist largely of ________, whereas pathogenic prions have more ________ regions.
71)
_____________
ESSAY. Write your answer in the space provided or on a separate sheet of paper.
72)
Explain the relationship between the terms virus particle, virion, and virus genome.
73)
Explain the difference between an enveloped virus and a naked virus.
74)
Why might a virus undergo lysogeny rather than the lytic cycle?
75)
How does efficiency of plating affect plaque-forming units?
76)
Explain viral replication in terms of an eclipse period, maturation, latent period, release, lysis, and burst size.
77)
Describe the structure of the T4 virus, and explain this virus’s attachment and penetration processes in terms of this structure.
78)
Describe the process whereby dsDNA viruses are replicated.
79)
Using T4 virions as a model, explain the concept of circular permutation.
80)
Describe the establishment and maintenance of the lysogenic state in the lambda phage.
81)
Explain the concept of a persistent infection in terms of a virus-infected cell.
82)
Describe the seven steps of retroviral replication.
83)
Because a prion is composed entirely of protein, explain how the prion replicates.
84)
Explain why some viruses contain enzymes within the virion and others do not.
85)
Explain how to determine the number of plaque-forming units in a virus sample.
86)
Why is uncoating a step in the replication cycle of some animal viruses?
87)
What do viroids lack that viruses have, and how does this influence their ability to infect a host cell?
88)
In the context of biogeochemical cycling, explain the role of bacteriophages and their impact on carbon cycling in the oceans.
1)
C
2)
B
3)
C
4)
A
5)
A
6)
D
7)
A
8)
B
9)
D
10)
D
11)
A
12)
B
13)
C
14)
D
15)
C
16)
A
17)
C
18)
C
19)
D
20)
D
21)
C
22)
D
23)
D
24)
C
25)
C
26)
D
27)
B
28)
TRUE
29)
TRUE
30)
TRUE
31)
FALSE
32)
TRUE
33)
TRUE
34)
TRUE
35)
FALSE
36)
FALSE
37)
TRUE
38)
TRUE
39)
TRUE
40)
FALSE
41)
TRUE
42)
TRUE
43)
TRUE
44)
FALSE
45)
FALSE
46)
TRUE
47)
infection
48)
bacteria
49)
helical / icosahedral
50)
their genome composition / mRNA transcript synthesis method (either order)
51)
host’s cell membrane / viral genes
52)
lysozyme
53)
tissue or cell cultures
54)
virus infectious unit
55)
plaque / one initial virion
56)
glucosylation / methylation (either order)
57)
reverse transcription
58)
lambda integrase
59)
necessary for replication of viral nucleic acid / those found in the protein coat
60)
permissive host
61)
T4 lysozyme / degrading the host’s peptidoglycan layer
62)
controls whether the lytic or the lysogenic pathway is followed during infection
63)
production of all late proteins must be prevented / a copy of the lambda virus genome must be integrated into the host chromosome (either order)
64)
lambda repressor (cI protein)
65)
cytosine in its genome / host defenses
66)
defective, or satellite, viruses
67)
lack a cell wall
68)
nucleic acid / protein
69)
titer
70)
prions
71)
α-helices / β-sheet
72)
A virus particle is a broad term used to describe a virus at any stage of infection, whereas a virion is one single virus particle that is at an infectious state. They are metabolically inert in both cases and minimally contain a DNA- or RNA-based genome and a protein capsid layer. A viral genome is packaged within both a virus particle and a virion, containing a single or double stranded nucleotide sequence that serves as a template to produce viral transcripts and ultimately their proteins.
73)
A naked virus lacks an envelope and is called a nucleocapsid, because it contains only a nucleotide-based genome and capsid proteins. A virus containing a nucleocapsid enveloped within an additional lipid layer is called an enveloped virus.
74)
Answers will vary, but one idea discussed might be that lysogeny allows the virus to increase in numbers within a host. After cell lysis, expelled viruses then must attach to a new host to proliferate, and if the viral host is in low numbers, the rate of proliferation would likely be low relative to a lysogenic virus.
75)
The issue of plating efficiency is that not every virus will be active at lysing the host in the medium. Consequently, the number of plaques observed is expected to be less than the actual number of viral particles in the plating. The plating efficiency therefore is required when counting plaque-forming units per volume plated to calculate the viral concentration (or titer).
76)
Figure 9.8 illustrates all five steps in the viral replication cycle. The first step involves the virus adsorbing to the host cell such that it becomes undetectable in the medium, termed an eclipse period. Once the genome has been injected into the host, maturation occurs of newly synthesized viral genomes as well as capsids. The time where replicated viruses remain in the host is called the latent period, which ends once the viruses are released. The host cell lyses, and the replicated viruses are released. If 18 viruses are released per host cell, then the burst size is 18.
77)
The T4 phage has a very complex structure, containing a head, collar, tail, tail pins, an endplate, and tail fibers. The tail fibers bind to polysaccharides within a Gram negative cell envelope for attachment. When the tail fibers retract, the tail pins bind to the host so that the tail itself interacts with the cell wall. A viral enzyme then forms a small pore within the host, and once the tail’s covering is contracted the viral dsDNA genome is inserted into the host’s cytoplasm. This infection mechanism is illustrated in Figure 9.10 in the textbook.
78)
The asymmetric processing of dsDNA amplification via rolling circle is highlighted in Figure 9.19 in the textbook. The two major steps involved are nicking of the dsDNA. The non-nicked strand uses a primer and polymerase to amplify the complementary strand as a concatemer.
79)
A linear concatemer is first formed after recombination of several copies of the genome. An endonuclease then cuts out particular regions of the concatemer to form individual linear replicated genomes. Although the genomes will all contain the same genes, this circular permutation process generates the genes in a different sequence order.
80)
Lambda phage, once circularized by matching its cohesive ends, integrates into an E. coli host genome by targeting the attλ gene in the host genome. The att gene in lambda’s genome then base pairs with the complementary sequences found in the attλ gene, and the lambda genome is inserted in the presence of an integrase catalyst. After the lambda genome is established in the host’s genome, it is maintained along with the E. coli genome through replication.
81)
Persistent viral infections occur when the host cell remains alive and continually produces more viruses. These conditions are especially common in animal cells when a persistent virus is coated with an envelope.
82)
Each of the seven steps is outlined in Figure 9.24 in the textbook. Once the retrovirus fuses to its host, the viral envelope is uncoated so that ssRNA is exposed. Reverse transcription then occurs to generate dsDNA that becomes integrated into the host’s genome. The host’s genome is transcribed into ssRNA along with the viral insert, and the viral mRNAs transcribed are encapsidated again to form more retroviruses. Progeny virions are released through a budding process within the host’s cell membrane.
83)
The sheer presence of a pathogenic prion induces the refolding of avirulent prions into proteins that are infectious.
84)
In the example of retroviruses, the reverse transcriptase enzyme, which is critical for its replication is found within the virion itself. However, many other viruses do not carry enzymes simply because they use the host’s cellular machinery to translate enzymes that they require.
85)
First, several plates containing the host are grown as a lawn on a suitable medium. Then different dilutions, often samples from a 10-fold serial dilution, are poured over the host cells. After incubation the number of plaques are counted, and the number of plaque forming units (pfu) per volume can then be calculated. Previously determined plating efficiency and the dilution factors must both be considered when calculating pfu per volume.
86)
The genome is freely available for replication only once a virion is uncoated and its contents are exposed.
87)
A viroids does not have a protein capsid covering and protecting its genome. This also means that viroids cannot actively infect a healthy host cell due to a lack of attaching structures. Viroids can, however, infect wounded cells. A viroid infection, for example, could occur after a plant cell wall has already been disrupted from an insect.
88)
Viruses that infect bacteria and lyse them are an integral part to cycling carbon in a system such as an ocean, where bacteria are abundant. This cell lysis frees up carbon stored in the cells as well as their cellular debris, which both provide a system with usable carbon substrates for others to use and proliferate.
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