microbio lecture 10 Flashcards
1
Q
viruses are genetic information (DNA or RNA) contained within
A
protective protein coat
2
Q
Inert particles
A
no metabolism, replication, motility
3
Q
genome hijacks
A
host cell’s replication machinery
4
Q
inert outside cells
A
inside, direct activities of cell
5
Q
viruses are
A
Infectious agents, not organisms
6
Q
viruses require
A
live organisms as hosts; cannot be grown in pure
culture
7
Q
viruses cannot be seen w/
A
light microscopy
8
Q
viruses classified generally based on
A
type of cell they infect: eukaryotic
or prokaryotic
9
Q
Viruses that infect bacteria are called
A
bacteriophages, or phages
10
Q
Phages easy to grow in the lab as a good model for how animal viruses
A
interact with their hosts
11
Q
phages are vehicle for
A
horizontal gene transfer
12
Q
phage ability to kill bacteria
is important
A
ecologically
and medically
13
Q
virion (viral particle) is
A
nucleic acid surrounded by a capsid
14
Q
capsid
A
protein coat
15
Q
capsid composed of simple identical subunits called
A
capsomeres
16
Q
Capsid plus nucleic acids called
A
nucleocapsid
17
Q
Nucleic acid is either ___,___
A
DNA or RNA
18
Q
nucleic acid may be
A
circular or linear, single- or double-stranded
19
Q
Enveloped viruses
A
surrounded by
lipid bilayer obtained from host cell
20
Q
enveloped virus have
A
Matrix protein between
nucleocapsid and envelope
21
Q
Non-enveloped (naked) viruses
A
are more resistant to disinfectants
22
Q
spikes
A
attach to receptor sites on host cells; phages attach by tail fibers
23
Q
three shapes of viral architecture
A
icosahedral, helical, complex
24
Q
icosahedral
A
20 flat triangles
25
helical
Capsomeres arranged in helix
26
complex
* Phage
* Icosahedral nucelocapsid (head) and helical protein (tail)
27
International Committee on Taxonomy of Viruses (ICTV) keeps
online database and publishes features, classification, nomenclature of viruses
28
2015 report
>6,000 viruses → 3,704 species → 609 genera
→ 27 subfamilies → 111 families →7 orders
29
Viruses: Key characteristics include
genome structure (nucleic acid and
strandedness) and hosts infected
30
in taxonomy, other characteristics like ___ are considered
for example, viral shape, disease
symptoms
31
DNA Viruses: Double Stranded DNA. Papillomaviridae
Non-enveloped, look at figure for shape, Human papillomaviruses (some types cause warts; others cause cancers)
32
DNA Viruses: Double Stranded DNA. Herpesviridae
Enveloped, look at figure for shape, Herpes zoster virus (chickenpox); herpes simplex viruses (cold sores, genital
herpes)
33
RNA Viruses: Doubled Stranded. Reoviridae
Non-enveloped, look at figure for shape, Human rotaviruses (diarrheal disease)
34
RNA Viruses: Single Stranded (plus strand). Picornaviridae
Non-enveloped, look at figure for shape, Polioviruses (poliomyelitis); rhinovirus
(colds); hepatitis A virus (hepatitis A)
35
RNA Viruses: Single Stranded (plus strand). Caliciviridae
Non-enveloped, look at figure for shape, Norovirus (gastroenteritis)
36
RNA Viruses: Single stranded (plus strand), Coronaviridae
Enveloped, look at figure for shape, Severe acute respiratory syndrome coronavirus (SARS), Middle East respiratory syndrome coronavirus (MERS)
37
RNA Viruses: Single stranded (minus strand), Rhabdaviridae
Enveloped, look at figure,
Enveloped Rhabdoviridae Rabies virus (rabies)
38
RNA Viruses: Single stranded (minus strand), Paramyxoviridae
Enveloped, look at figure, Mumps virus (mumps); measles virus (measles)
39
RNA Viruses: Single stranded (minus strand), Orthomyxoviridae
Enveloped, look at figure, Influenza virus (influenza)
40
Reverse transcribing viruses (retroviruses) - DNA, Hepadnoviridae
Enveloped, look at figure, Hepatitis B virus (hepatitis B)
41
Reverse transcribing viruses (retroviruses) - RNA, Retroviridae
Enveloped, look at figure, Human immunodeficiency virus (AIDS)
42
Virus families end in suffix
-viridae
43
Do names follow a consistent pattern?
no
44
some names indicate...
appearance (for example, Coronaviridae from
corona, meaning “crown”)
45
Others named for ____ ___ from which first isolated
geographic area (for
example, Bunyaviridae from Bunyamwera in Uganda, Africa)
46
Genus ends in
-virus (for example, Enterovirus)
47
Species name often name of ______
disease
For example, poliovirus causes poliomyelitis
* Viruses commonly referred to only by species name
48
Viruses often referred to
informally
49
Groups of unrelated viruses sharing....
routes of infection
50
Oral-fecal route:
enteric viruses
51
Respiratory route:
respiratory viruses
52
Zoonotic viruses cause
zoonoses (animal to human)
53
Arboviruses (from arthropod borne) are spread by
arthropods; often can infect widely different species
54
Arboviruses can cause diseases such as
yellow fever, dengue fever, West
Nile encephalitis, La Crosse encephalitis
55
Enteric: mechanism of transmission; common viruses transmitted
Fecal-oral route; Enteroviruses (polio), noroviruses, rotaviruses (diarrhea)
56
Respiratory: mechanism of transmission; common viruses transmitted
Respiratory or salivary route; Influenza, measles, rhinoviruses (colds)
57
Sexually transmitted: mechanism of transmission; common viruses transmitted
Sexual contact; Herpes simplex virus type 2 (genital herpes), HIV
58
Zoonotic: mechanism of transmission; common viruses transmitted
Vector (such as arthropods); West Nile encephalitis, Zika virus disease, dengue fever
59
Zoonotic: mechanism of transmission; common viruses transmitted
Animal to human directly; Rabies, cowpox
60
Three general types of bacteriophages based on
relationship with host
Lytic (virulent) phages
Temperate phages
Filamentous phages
61
General strategies of phage replication
Productive Infection; Latent State
62
Productive infection
New viral particles are produced
63
Latent state
Viral genome remains silent within cell, but is replicated along with host cell genome
64
Lytic or virulent phages exit host by
lysing the cell
65
T4 phage (dsDNA) is model, entire process takes
approximately 30 minutes
66
Infection cycle is five step process
* Attachment
* Genome entry
* Synthesis
* Assembly
* Release
67
Attachment
* Phage attaches to receptors
* Receptors are molecules that
typically perform other functions
* Cells that lack specific receptor
are resistant to infection by that
phage
68
Genome entry
* T4 lysozyme degrades cell wall
* Tail contracts, injects genome
through cell wall and membrane
* Capsid remains outside the cell
69
Synthesis of phage proteins and genome
* Early proteins translated within minutes; nuclease degrades host DNA
* Phage genome synthesized
* Late proteins are structural proteins
(capsid, tail); produced toward end of cycle
70
Assembly (maturation)
Some components assemble
spontaneously, others require
protein scaffolds
71
Release
* Lysozyme produced late in
infection; digests cell wall
* Cell lyses, releases phage
* Burst size of T4 is approximately
200
72
Temperate phages can direct a
lytic infection or incorporate their DNA into host cell genome
(lysogenic infection)
73
infected cell is
lysogen
74
integrated phage DNA is
prophage
75
When the cell divides, the prophage
is replicated
76
Prophage can begin process of
lytic infection
77
Metabolic state of host cell can influence
type of infection
78
Lambda phage is
model
79
Phage-encoded enzyme integrase inserts phage DNA at
specific site on host chromosome
80
Prophage replicates along with
host chromosome
81
Phage- encoded enzyme can be excised by phage
encoded enzyme, resulting
in
lytic infection
82
A phage encoded repressor prevents
excision, maintains lysogenic state
83
Lambda phage
DNA excised from chromosome only about
once per 10,000 divisions of lysogen
84
if DNA damaged (for example, UV light exposure), then..
SOS repair
system turns on, activates a protease
85
Protease destroys repressor, allows
prophage to be
excised, enter lytic cycle
86
phage induction
allows phage escape
damaged host
87
Lysogen is immune to
superinfection (infection by same
phage)
88
Repressor maintaining integrated prophage also binds to
operator on incoming phage DNA, prevents gene expression
89
Lysogen may show change in phenotype due _______ called lysogenic conversion
to prophage DNA
90
Toxins encoded by phage genes; only strains carrying ________ produce the toxins
prophage
91
Corynebacterium: Medical importance, Property encoded by phage
Causes diphtheria; Diptheria toxin
92
Escherichia coli O157:H7: Medical importance, Property encoded by phage
Causes hemolytic uremic syndrome; Shiga toxin
93
Streptococcus pyogenes: Medical importance, Property encoded by phage
Causes scarlet fever; Streptococcal pyrogenic exotoxins(SPEs)
94
Vibrio cholerae: Medical importance, Property encoded by phage
Causes cholera; Cholera toxin
95
Filamentous Phages
Single-stranded DNA phages
* Look like long fibers
* Cause productive infections
* Host cells not killed, but grow
more slowly
96
Filamentous Phages continued
* M13 phage is model
* Attaches to protein on F pilus
of E. coli
* Single-stranded DNA
genome enters cytoplasm
97
In filamentous phages, DNA polymerase of host cells synthesizes complementary strand ->
Called replicative form (RF); one
strand used as template for synthesis
of mRNA, copies of genome
98
in filamentous phages, M13 particles assembled
in process of extrusion
* M13 phage coat protein molecules
inserted into cytoplasmic membrane
* Other proteins form pores
* As phage DNA secreted through
pores, coat proteins coat the DNA,
form nucleocapsids
99
Generalized Transduction
* Results from packaging error during phage assembly
* Some phages degrade host chromosome; fragments can
be mistakenly packaged into phage head
100
These phages cannot direct phage replication cycle
Called transducing particles
101
Following release, transducing particles can bind to
new host, inject DNA
102
DNA may integrate via homologous recombination, replacing
host DNA
103
Any gene from donor cell can be
transferred
104
Specialized Transduction
Excision mistake during transition from
lysogenic to lytic cycle of temperate
phage
* Short piece of bacterial DNA removed
105
In Specialized transduction, Excised DNA incorporated into
phage heads; defective particles released
106
Specialized transudction: bacterial genes may integrate via
homologous recombination
107
Specialized transduction: only bacterial genes adjacent to _____ ____ DNA transferred
integrated phage
108
Viruses multiply only inside _______
living cells
109
must cultivate suitable ____ ____ to grow viruses
host cells
110
Plaque assays
used to count phage particles in samples:
sewage, seawater, soil
111
Plaque assays: Soft agar inoculated with
bacterial host and phage-containing specimen
112
Plaque assays-> after inoculation,
Bacterial lawn forms
113
plaques
Zones of clearing from bacterial lysis
114
Plaque forming unit (PFU) represents
single phage
115
counting plaques yield the titer, which is
concentration of
phage in the original sample
116
Animal Virus Replication: Attachment
* Viruses bind to receptors on host cell surface, usually
glycoproteins on cytoplasmic membrane
* Often more than one receptor attachment is required (for
example, HIV binds to two)
* Normal function of receptor molecule unrelated to viral infection
117
During attachment of animal virus replication, particular viruses must attach to
specific receptor; limits cell types and tissues a virus can infect
118
In attachment of animal virus replication, Most viruses infect a
single species (dogs do not contract
measles from humans), but that is not always true (rabies
virus infects dogs and humans)
119
Animal Virus replication: Penetration and uncoating
* Enveloped viruses enter by fusion or endocytosis
* Non-enveloped viruses cannot fuse
* Entire virion enters cell; nucleic acid separates from protein coat in process of uncoating
120
Animal Virus Replication: Synthesis
* Expression of viral genes to produce viral structural and
catalytic genes (for example, capsid proteins, enzymes
required for replication)
* Often synthesized as polyprotein that is cleaved by viral
proteases (a target site of antiviral medications)
121
Synthesis of multiple copies of genome
* Three general replication strategies depending on type of genome of virus
122
Three strategies depending on type of genome of virus
* DNA viruses
* RNA viruses
* Reverse transcribing viruses
123
Replication of dsDNA viruses
* dsDNA (+/ −) is replicated to form viral genome
* (−) strand transcribed to produce mRNA; translated to make viral
proteins
124
Replication of ssDNA viruses
* Complement to ssDNA synthesized first; then acts as template to
produce more copies of viral genome
* (−) strand transcribed to produce mRNA
125
Replication of RNA viruses
* Majority are single-stranded; replicate in cytoplasm
* Require virally encoded RNA-dependent RNA polymerase
(replicase)
126
Replicase allows use of
RNA template to make new strand of RNA
127
Replication strategy varies with viral genome
for +, -, or +/-
128
(+) ssRNA genome also serves as
mRNA
129
(−)ssRNA genome is complement to
mRNA
130
(+/ −) dsRNA genome contains
both
131
Replication of (+) ssRNA viruses
* Viral RNA binds to ribosome; produces viral replicase
* Viral replicase produces multiple copies of complementary (−)
* RNA strand
132
(+) ssRNA viruses replicated act as
templates to produce more (+) strands: Can serve as viral genome or be translated to produce viral proteins
133
Replication of (−) ssRNA viruses
Viral RNA and replicase both enter host cell to make complementary (+) RNA strand (REPLICASE MUST ACCOMPANY VIRUS SINCE FIRST STEP IS TO
MAKE (+) STRAND)
134
In (-)ssRNA replication, (+) RNA strand can serve as
mRNA to make viral proteins
135
Multiple copies of complementary (−) RNA strand produced to serve as
viral genome
136
Replication of dsRNA viruses
* Replicase enters host cell with dsRNA because host cell cannot translate
dsRNA
* Replicase uses (−) RNA strand to produce (+) RNA strand
* (+) RNA strand can serve as mRNA to make viral proteins
137
Replication of RNA viruses
Replicase lacks proofreading ability
138
Poor proofreading ability in RNA viruses
* Generates mutations during replication
* Mutations in surface proteins may not be recognized by immune
system
139
Antigenic drift
antigenic variation because of replicase poor proofreading
140
Some RNA viruses have segmented genomes. When two different viruses or strains infect a host....
new viral particles may contain segments from each virus
141
antigenic shift
New subtype results from this reassortment of RNA viruses segmented genomes
142
Replication of reverse-transcribing viruses
* Encode reverse transcriptase: makes DNA from RNA
* Retroviruses have (+) ssRNA genome (such as HIV)
143
Reverse transcriptase enters the
cell and synthesizes a single DNA
strand from RNA template
144
As the Complementary DNA strand synthesized,
dsDNA integrated into
host cell chromosome
145
Can be transcribed to produce .....
new viral genome, mRNA
146
Animal Virus Replication: Assembly and maturation
* Spontaneous self-assembly when viral nucleic acid and capsid proteins accumulate in host cell
* Site of assembly varies with virus type and affects release
147
Animal Virus Replication: Release
* Most enveloped viruses leave via budding
* Non-enveloped viruses released when host cell dies, often by apoptosis initiated by virus or host
148
Budding
* Viral protein spikes insert into host cell membrane; matrix
proteins accumulate; nucleocapsids extruded
* Covered with matrix protein and lipid envelope
* Some obtain envelope from organelles
149
The World Health Organization (WHO) named the novel
coronavirus that causes the disease COVID-19....
“severe acute respiratory syndrome coronavirus 2” (SARS-CoV-2) in January 2020.
150
The disease is named from a contraction of the term
coronavirus disease 2019.
151
This disease was first observed in humans in
Wuhan, China in December 2019.
152
The WHO declared COVID-19 a Public Health Emergency of International Concern (PHEIC) on
January 30th, 2020
153
Three β-coronaviruses have crossed the species barrier since 2000
SARS-CoV
MERS-COV
SARS-CoV-2
1. SARS-CoV emerged in the Guangdong province of China in 2002 ultimately infecting
8,098 people and causing 774 deaths across 5 continents
2. Middle-East respiratory syndrome coronavirus (MERS-CoV) emerged in the Arabian
peninsula in 2012 and remains a public health concern
3. SARS-CoV-2 was identified in December 2019
154
Both SARS-CoV and SARS-CoV-2 likely originated from
bats as the reservoir,
with small mammals as intermediate hosts between bat and human
155
MERS-CoV originated from
a camel reservoir with direct transfer to humans.
156
In addition, four low-pathogenicity coronaviruses are
endemic in humans.
157
SARS-CoV-2 characteristics: The S proteins
protrude from the viral surface resembling a
crown, or corona
158
SARS-CoV-2 belongs to the genus
β-coronavirus, family Coronaviridae
159
SARS-CoV-2 is a _____, with a length of ______
enveloped virus with an unsegmented single-stranded positive-sense RNA genome; 30 kb
160
SARS-CoV-2 main structural proteins
* spike (S) glycoproteins
* envelope (E) glycoproteins
* membrane (M) glycoproteins
* nucleocapsid (N) proteins
161
The genome also codes for
16 nonstructural proteins that are involved in
viral replication, maturation, and release.
162
Scientists published the genome sequence by
January 10, 2020, just one
month after it was first reported; it took over a year to sequence the SARS-
CoV in 2003.
