Chapter 13 Flashcards
(185 cards)
1
Q
simply genetic information
A
viruses
2
Q
no metabolism, replication, motility
A
Inert particles
3
Q
Genome hijacks what
A
host cell’s replication machinery
4
Q
Viruses require what as hosts
A
live organisms
5
Q
infect prokaryotes
A
Bacteriophages (phages)
6
Q
are viruses small or big
A
small
7
Q
complete viral particle outside host
A
Virion
8
Q
Protein coat is
A
capsid
9
Q
Composed of identical
subunits called
A
capsomeres
10
Q
Capsid + nucleic acids: called
A
nucleocapsid
11
Q
have lipid bilayer envelope
A
Enveloped viruses
12
Q
between nucleocapsid and envelope
A
Matrix protein
13
Q
viruses lack envelope; more
resistant to disinfectants
A
Non-enveloped (=naked)
14
Q
either DNA or RNA, never both
A
Viral genome
15
Q
Viruses have protein components for attachment to
A
receptor sites on host cells
16
Q
Phages attach by
A
tail fibers
17
Q
Generally three different shapes Viruses
A
Icosahedral, helical, or complex
18
Q
appear spherical with EM
A
Icosahedral (20 flat triangles)
19
Q
appear cylindrical
A
Helical (helix arrangement)
20
Q
publishes classification of
viruses
A
International Committee on
Taxonomy of Viruses (ICTV)
21
Q
is analogous to domain
A
Realm
22
Q
Key characteristics include
A
genome structure (nucleic
acid and strandedness) and hosts infected
23
Q
Virus families end in suffix what
A
-viridae
24
Q
from corona,
meaning “crown”
A
Coronaviridae
25
Viruses commonly referred to only by
species name
26
Oral-fecal route
enteric viruses
27
Respiratory route
respiratory viruses
28
cause zoonoses (animal to human)
Zoonotic
29
are spread by arthropods;
often can infect widely different species
Arboviruses
30
Three general types of bacteriophages based on
relationship with host
* Lytic (virulent) phages
* Temperate phages
* Filamentous phages
31
General strategies for phage replication
* Productive infection
* Latent state
32
New viral particles are produced
Productive infection
33
Viral genome remains silent within cell, but is replicated along with host cell genome
Latent state
34
exit host
* Cell is lysed
Lytic or virulent phages
35
new particles
formed
Productive infection:
36
Five step process of Lytic Phage Infections
* Attachment
* Genome entry
* Synthesis
* Assembly
* Release
37
* Phage attaches to a bacterial receptors using its tail
* Receptors are molecules that typically perform other functions
* Cells that lack specific receptor are resistant to infection by
that phage
Attachment
38
* T4 lysozyme degrades cell wall
* Tail contracts, injects genome
through cell wall and membrane
* Capsid remains outside
Genome entry
38
translated within minutes; nuclease degrades host DNA
Early proteins
39
are structural proteins (capsid, tail); produced toward end of cycle
Late proteins
40
Some components spontaneously
assemble, others require protein
scaffolds
Assembly (maturation)
41
* Lysozymes produced late in infection; digests cell wall
* Cell lyses, releases phage
* Burst size of T4 is ~200
Release
42
Temperate Phage Infections
* Option of lytic infection or incorporation of DNA into host cell genome
* Resulting circular molecule either directs lytic infection or
integrates into E. coli chromosome
* Phage enzyme integrase inserts DNA at specific site
* A prophage can remain in latent state indefinitely
* The host protease destroys viral
repressor and allows the prophage to be excised and enter lytic cycle
* Called phage induction;
43
Infected cell is lysogen
Lysogenic infection
44
➢ Double-stranded DNA
phage that infects E.coli
➢ Linear chromosome
➢ Complementary single-
stranded overhangs at
ends, join inside host
Lambda (λ) phage
45
inserts DNA at specific site
Phage enzyme integrase
46
Integrated phage DNA
prophage
47
Most prophage genes are silent because a phage-encoded
repressor
48
A prophage can remain in latent state for how long
indefinitely
49
DNA excised from chromosome only about once per 10,000 divisions of lysogen
Lambda (λ) phage:
50
allows phage to escape damaged host
phage induction
51
Lysogeny consequences:
Lysogen immune to superinfection
Lysogenic conversion
52
infection by same phage
* Repressor maintaining integrated prophage also binds to operator on incoming phage DNA
superinfection
53
Change in phenotype of lysogen due to prophage carried
Lysogenic conversion
54
* Single-stranded DNA phages
* Look like long fibers
* Cause productive infections
Filamentous Phages
55
Double-stranded DNA is called th
replicative form (RF)
56
how Filamentous Phages work
Host DNA polymerase synthesizes complementary strand
* One strand is used to make mRNA and copies of the phage
single-stranded genome
* M13 phage capsomeres are inserted into host’s cytoplasmic membrane
* Other phage proteins form pores in cell envelope
* As phage DNA is extruded
through pores, capsomere coat
DNA, to form a nucleocapsid
57
One strand is used to what
make mRNA and copies of the phage single-stranded genome
58
M13 phage capsomeres are inserted into
host’s cytoplasmic membrane
59
Other phage proteins form pores in
cell envelope
60
As phage DNA is extruded
through pores, capsomere coat
DNA, to form a
nucleocapsid
61
transfer of DNA from one bacteria to another by a virus
Generalized Transduction
62
Results from packaging error during phage assembly
Generalized Transduction
63
Some phages degrade what
host chromosome;
host fragments packaged by mistake
64
can Generalized Transduction phages direct phage replication cycle
no
65
DNA may integrate via
homologous recombination,
replacing host DNA
66
can any gene be transfer in Generalized Transduction
yes
67
Specialized Transduction
* Excision mistake during
transition from lysogenic to
lytic cycle of temperate phage
* Short piece of flanking
bacterial DNA removed; piece
of phage DNA remains in host
chromosome
* Excised DNA incorporated
into phage heads; defective
particles released
* Can bind to new host,
inject DNA
* Bacterial genes may
integrate via homologous
recombination
* Only bacterial genes
adjacent to integrated
phage DNA transferred
68
Excision mistake during
transition from lysogenic to
lytic cycle of temperate phage
Specialized Transduction
69
what is removed from Specialized Transduction
Short piece of flanking
bacterial DNA
70
what remains in host chromosome
piece
of phage DNA
71
incorporated
into phage heads
Excised DNA
72
what is released
defective
particles
73
Bacterial genes may
integrate via what in Specialized Transduction
homologous
recombination
74
what genes can be transferred in Specialized Transduction
Only bacterial genes
adjacent to integrated
phage DNA transferred
75
Viruses multiply only inside
living cells
76
used to quantitate phage particles in samples:
sewage, seawater, soil
plaque assays
77
Zones of clearing from
bacterial lysis are
plaques
78
Counting plaque forming
units (PFU) yields
titer
79
80
can slow the progression of a viral infection
antiviral medications
81
what are the steps of Five-step infection cycle
Attachment, genome entry, synthesis,
assembly and release
82
bind to receptors on host
cell surface
Virus attachment proteins
83
separation from protein coat
Entry and uncoating
84
how do virus enter the cell
fusion with the host membrane
85
can Non-enveloped viruses fuse with the host membrane
no
86
what do Non-enveloped viruses do instead to enter cell
endocytosis
"Entire virion taken into the cell"
87
Expression of viral genes to produce viral structural and catalytic genes
Synthesis
88
Most DNA viruses multiply in
nucleus
89
Three general replication strategies depending on type of
genome of virus
– DNA viruses
– RNA viruses
– Reverse transcribing viruses
90
Process of replication for DNA viruses
* in nucleus
* Use host cell machinery
* DNA viruses encode their own DNA polymerase so they can
replicate even if the host is not
91
what do DNA viruses encode so that they can replicate even if the host is not
DNA poly
92
they can replicate even if the host is not
viral genome
93
(−) strand transcribed to produce
mRNA
94
(−) strand translated to make
viral proteins
95
Complement to DNA synthesized first; then acts as template
to produce more copies of viral genome
ss DNA viruses
96
Replication of RNA viruses
* Replication in the cytoplasm
* Require virally-encoded RNA-dependent RNA polymerase: replicase
✓ Synthesizes RNA from RNA template
* Replication strategy varies with viral genome
97
where do RNA viruses replicate
cytoplasm
98
virally-encoded RNA-dependent RNA polymerase
replicase
99
(+) single stranded RNA genome also serves as
mRNA
100
(−) single stranded RNA genome is complement to
mRNA
101
(+/ −) double stranded RNA genome contains
mRNA and complement
102
Replication of ss (+) RNA viruses
* Viral RNA binds to host ribosomes; produces viral replicase
* Viral replicase makes multiple copies of complementary (-)
RNA strands
➢ They act as a template to produce (+) RNA strands (i.e. new
virions formed)
➢ Or are translated to produce viral proteins
103
binds to host ribosomes
Viral RNA
104
Viral RNA prodeces what
viral replicase
105
makes multiple copies of complementary (-)
RNA strands
viral replicase
106
viral replicase makes multiple copies of what
complementary (-) RNA strands
107
they act as a template to produce (+) RNA strands
Viral replicase
108
s (+) RNA viruses are tranlated to make
viral proteins
109
Replicase is used to synthesize
(+) strand RNA
110
(+) RNA strand can serve as mRNA to make
viral protein
111
(+) RNA strand used to make
(-) RNA strands to
serve as new viral genomes
112
A molecule of replicase is packaged with the
(-) strand
113
Replication of ds RNA viruses
* Carry their own replicase because host cannot
translate double-stranded RNA
– Replicase use (-) RNA strand as template to make
(+) RNA strand
– (+) RNA strand can serve as mRNA to be translated
into viral proteins and more replicase is made
114
why do ds RNA viruses carry their own replicase
because host cannot
translate double-stranded RNA
115
Replicase use (-) RNA strand as template to make
Replicase use (-) RNA strand as template to make
(+) RNA strand
116
can serve as mRNA to be translated
into viral proteins and more replicase is made
(+) RNA strand
117
lack proofreading and make more mistake than DNA
polymerase
replicases
118
These mutations in surface proteins may not be recognized by
immune system
119
mutations affecting surface proteins recognized by
host immune system.
antigenic drift
120
the nucleic acid is present as segments
genomes
121
If two strains of a virus infect the same cell, new viral particles can have a combination of RNA segments from
either parent stains (=
reassortment
122
Replication of reverse-transcribing viruses
* Encode reverse transcriptase: an RNA-dependent DNA
polymerase that makes DNA from RNA
* Retroviruses have ss (+) RNA genome (ex: HIV)
* Reverse transcriptase is carried within the virion and
synthesizes single DNA strand from the RNA template
(after entering the cell)
* Complementary DNA strand is synthesized
* dsDNA integrated into host cell chromosome
* Can be transcribed to produce new viral genome, mRNA
* Viral DNA can direct productive infection or remain latent
* Once the DNA copy is made, it cannot be eliminated from
the cell!
123
an RNA-dependent DNA
polymerase that makes DNA from RNA
reverse transcriptase:
124
Retroviruses have what genome
ss (+) RNA genome
125
is carried within the virion and
synthesizes single DNA strand from the RNA template
Reverse transcriptase
126
Complementary DNA strand is
synthesized
127
integrated into host cell chromosome
dsDNA
128
Viral DNA can of reverse-transcribing viruses can do two things
direct productive infection or remain latent
129
once the copy of the cell is made can it be eliminated
no
130
Assembly (maturation)
* Protein capsid forms; genome & enzymes packaged
* Site of assembly varies with virus type:
➢ Non-enveloped virus: mature fully in the cytoplasm
➢ Enveloped virus: maturation occurs as it leaves host cell
* Very similar process for most viruses
* Spontaneo
131
Non-enveloped virus: mature fully in the
cytoplasm
132
Enveloped virus: maturation occurs
as it leaves host cell
133
Release
* Enveloped viruses are released via budding
➢ Viral protein spikes insert into host cell membrane
➢ Matrix proteins accumulate on the inside surface
➢ Nucleocapsid extruded; covered with matrix protein and lipid
envelope
➢ Some obtain envelope from organelles
* Non-enveloped viruses released when host cell dies, often
by apoptosis initiated by virus or host.
134
Enveloped viruses are released via
budding
135
insert into host cell membrane
Viral protein spikes
136
Non-enveloped viruses released when host cell dies, often
by
apoptosis
137
* Rapid onset; Short duration
* Burst if virion released from infected host cells
* Immune system gradually eliminates virus
Acute Infections
138
* Continue for years or lifetime
* May or may not have symptoms
Persistent Infections
139
types of Persistent Infections
chronic or latent
140
Continuous production of low levels of virus particles
Chronic infections
141
what is known about Chronic infection's carriers
- Carrier my lack symptoms
- Carrier may still transmit virus
142
- Viral genome remains silent in host cell
- Cannot be eliminated from the body; Can reactivate to cause
productive infection
Latent infections
143
Viral genome may be integrated into the host chromosome as
provirus
144
what disease do you get Only if previously had chickenpox, varicella zoster virus (VSV)
Shingles
145
is abnormal growth
tumor
146
can cancerous (malignant) tumors metastasize
yes
147
can benign tumors metastasize
no
148
Control of cell growth and division requires coordination of 2 sets of
genes
Proto-oncogenes
Tumor suppressor
149
stimulate cell growth
Proto-oncogenes
150
genes inhibit growth
Tumor suppressor
151
Mutations in these genes cause abnormal and/or uncontrolled growth
Tumor
152
is proto-oncogenes that has been changed to promote uncontrolled growth
Oncogenes
153
Numerous events, including spontaneous and induced mutations, can lead to conversion into an
Oncogenes
154
viruses that can cause cancer in
humans
Oncoviruses (oncogenic)
155
things to note about
Oncoviruses (oncogenic)
* May arise directly from viral infection
* Most virus-induced tumors associated with DNA viruses
* Most virus-induced tumors associated with DNA viruses
156
Most virus-induced tumors associated with DNA viruses
Oncoviruses
157
Cancers caused by the viruses do not develop immediately when do they present
Present 15 to 40 years after infection
158
Oncolytic viruses specifically target and kill
cancer cells
159
Oncolytic viruses destroy cancer how?
* Destroy the cancer cells directly by multiplying within them and
causing lysis
* Others
160
In 2015, the Food and Drug Administration (FDA) approved a
genetically engineered herpes simplex virus type 1 to treat
advanced inoperable melanoma
161
viruses must be grown where
in appropriate host
162
Many viruses cause distinct morphological alterations called
cytopathic effect
163
Cells may change shape, detach from surface, lyse, fuse into giant
multinuclear cell (syncytium), or form
inclusion body
164
site of viral replication
inclusion body
165
dilutions of virus given to hosts
Quantal assay
166
some viruses cause red blood cells to
agglutinate (clump)
Hemagglutination
167
Highest dilution with maximum agglutination is
titer of the virus
168
Economically important, particularly when they affect crops
Plant Viruses
169
signs of Plant Viruses
* Yellowing of foliage, irregular lines on leaves and fruit
* Individual cells or organs may die
* Tumors may appear
* Stunted growth
* But growth may be stimulated leading to deformed structures
170
do plants recover from viral infections
no
171
may accumulate in enormous numbers
Virions
172
Difficult to eliminate from contaminated area
Virions
173
do plant viruses attach to cell receptors
no
174
how are plant viruses transmitted
soil; humans; insects; contaminated seeds, tubers, pollen; grafting
175
are small single-stranded RNA molecules that form a closed ring
Viroids
176
what do Viroids enter through
through wound sites
177
are proteinaceous infectious agents
prions
178
Human diseases caused by prions
Creutzfeldt-Jakob disease, fatal familial insomnia, and kuru
179
Animal diseases caused by prions
scrapie (sheep and goats), mad cow disease or bovine spongiform encephalopathy (cattle), and chronic wasting disease (deer and elk)
180
accumulate in neural tissue
Prion proteins
181
what happens Prion proteins accumulate in neural tissue
* Neurons die (unknown reason)
* Brain function deteriorates
* Tissues develop holes
182
Characteristic appearance gives rise to general term for all prion diseases
transmissible spongiform
encephalopathies
183
Can be easily destroyed by host proteases
PrPC (prion protein, cellular)
184
* Resistant to proteases; become insoluble, aggregate
* Unusually resistant to heat, chemical treatments
- PrPSC (prion protein, scrapie)
