Chapter 6 Flashcards
1
Q
What is a noncellular particle that must infect a host cell, where it reproduces?
A
Virus
2
Q
What does a virion consist of?
A
- a single nucleid acid
- contained in a capsid
3
Q
Are viruses specific or general in what kind of host cell they can affect?
A
- Specific; the hosts are limited to a particular host range of closely related strains or species
4
Q
What is a virus that infects bacteria called?
A
- bacteriophage
5
Q
What is the measles virus?
A
- a human virus
6
Q
What is the TMV?
A
- tobacco mosaic virus
- plant virus
7
Q
What happens after a RNA virus infects the cell?
A
- Virions are assembled within “virus factories”, virus-induced cell compartments called a replication complex
- Complexes move around within the cell
8
Q
Do viruses only replicate in the host?
A
- No some integrate their genomes into that of the host
9
Q
What is a prophage?
A
- a virus the integrates its genome into the DNA of a bacterial genome
10
Q
What is a provirus?
A
- an integrated viral genome within a human cell
11
Q
What is an endogenous virus?
A
- a permanently integrated provirus transmitted via the germ line
12
Q
What are the three different forms a virus may interconvert to?
A
- Virion
- Intracellular replication complex
- Viral genome integrated within host DNA
13
Q
What is the Virion form?
A
- an inert particle that does not carry out any metabolism or energy conversion
14
Q
What is the Intracellular replication complex form?
A
- Within a host cell, the virla gene products direct the cell’s enzymes to asseble progeny virions at “virus factories” called replication complexes
15
Q
What is the Viral genome integrated within host DNA form?
A
- This may be a permanent condition
16
Q
What type of virus is related to the lysogenic cycle?
A
provirus
17
Q
Do viruses play a role in the ecosystem?
A
yes
18
Q
How do acute viruses affect the ecosystem?
A
- act as predators or parasites to limit host population density - recycle nutrients from their host bodies
19
Q
How does Virus-associated mortality affect the ecosystem?
A
- they may increase the
genetic diversity of
host species
20
Q
How do persistent viruses affect the ecosystem?
A
- they may evolve traits
that confer positive
benefits in a virus-host
mutualism
21
Q
What role do viruses play in marine ecosystems?
A
- significant role in the cycling of food molecules - also important in carbon balance
22
Q
What is a host range?
A
- a particular group of
host species that a
virus can infect
23
Q
Are chronic or acute virus disease more common?
A
Chronic
24
Q
What keeps the viral genome intact and enables infection of the appropriate host cell?
A
- the structure of the
virion
25
What delivers the viral genome to the host cell?
- the capsid
26
What are Icosahedral viruses?
```
- polyhedral with 20
identical triangular
faces
- have a structure that
exhibits rotational
symmetry
```
27
What encloses some icosahedral viruses?
envelope
28
What does this envelope contain?
```
- glycoprotein spikes
(encoded by the virus)
- Tegument proteins (in
between the
envelope and capsid)
```
29
What are Filamentous viruses?
```
- capsid consists of a
long tube of protein
with genome coiled
inside
- vary in length
depending on genome
size
- include bacteriophages
as well as animal
viruses
- show helical symmetry
```
30
What is an example of a tailed virus?
- T4 bacteriophages
- Has an icosahedral
"head" and helical
"neck"
31
What are RNA viruses that lack capsid symmetry?
- Influenza viruses
- RNA segments are
coated with
nucleocapsid proteins
32
What is special about Poxviruses?
```
- Their genome is
surrounded by several
layers.
- large number of
accessory proteins
```
33
What contains so many enzymes that they appear to have evolved from degenerate cells?
- Large asymmetrical
| viruses
34
What are RNA molecules that infect plants?
Viroids
35
What are some characteristics of viroids?
- no protein capsid
- replicated by host
RNA polymerase
- catalytic ability
36
What are proteins that infect animals?
- Prions
37
What are some characteristics of prions?
```
- no nucleic acid
component
- abnormal structure
that alters the
conformation of other
normal proteins
```
38
Viral genomes can be:
- DNA or RNA
- Single or double-
stranded
-Linear or circular
39
What has key consequences for the mode of infection, and for the course of a viral disease?
- the form of the
| genome
40
What is the criteria that viruses are classified by?
- Genome Composition
- Capsid Symmetry
- Envelope
- Size of the virion
- Host range
41
David Baltimore proposed that the main distinctions among classes of viruses be:
- genome composition
- the route used to
express messenger
RNA
42
Group I
Double-stranded DNA viruses
43
Group II
Single-stranded DNA viruses
44
Group III
Double-stranded RNA viruses
45
Group IV
(+) single stranded RNA viruses
46
Group V
(-) single stranded RNA Viruses
47
Group VI
RNA retroviruses
48
Group VII
DNA paraetroviruses
49
How can the relatedness of different herpes viruses that evolved from a common ancestor be measured?
- by comparing their
| genome sequences
50
What is this comparison based on?
- Orthologs
- Genes of common
ancestry in two
genomes that share
the same function
51
What is useful for viruses because of their small genomes encode few proteins?
- Proteomic
| classification
52
What are gut bacteriophages called?
- Coliphages
- modulates human
digestion, the
immune system, and
mental health
53
What is mediated by cell-surface receptors?
- Contract and
| attachment
54
What are cell-surface receptors?
```
- Proteins that are
specific to the host
species and which
bind to a specific viral
component
- normally used for
important functions for
the host cell
```
55
True or False. Most bacteriophages inject only their genome into a cell through the cell envelope.
True
56
What are the two different life cycles that bacteriophages can undergo?
```
- Lytic Cycle: Virulent
Phage( kills host) ex)
T4
- Lysogenic cycle:
Temperate Phage
(forms prophage)
```
57
Steps of the Lytic replication cycle:
```
1. host recognition and
attachment
2. Genome Entry
3. Assembly of phages
4. Exit and transmission
```
58
What is a temperate phage?
```
- can infect and lyse
cells like a virulent
phage, but it also has
an alternative
pathway: to integrate
its genome as a
prophage
```
59
What is the state called lysogeny?
- Bacteriophage is
quiescent
- Can reactivate to
become lytic
60
How does a slow-release replication cycle differ from lysis and lysogeny?
- phage particles reproduce without destroying the host cell.
61
What extrudes individual progeny through the cell envelope?
- Filamentous phages
62
What are three types of defense mechanisms that bacteria have?
- genetic resistance
- restriction endonucleases
- CRISPR
63
What is genetic resistance?
- altered receptor proteins
64
What is restriction endonucleases?
- Cleave viral DNA lacking methylation
65
What is CRISPR?
- Clustered regularly interspaced short palindromic repeats
| - A bacterial immune system of sorts
66
What is the best understood phage community?
Gut Virome
67
Phage effects that are positive:
1. Phages may limit the bacterial numbers to levels that the human immune system can tolerate.
2. Phage particles may modulate immune system activity by suppressing T-cell activation and tumor formation.
3. Phages may attack biofilms
68
What determines Tropism?
- the receptors of the cell`
69
How do most animal viruses enter the host as?
- Mostly as virions
| - Internalized virions undergo uncoating, where genome is released from its capsid.
70
What is the primary factor determining the life cycle of an animal virus?
- the form of its genome
71
Replication Cycle: DNA Viruses
- can utilize the host replication machinery
72
Replication Cycle: RNA Viruses
- Use an RNA-dependent RNA-polymerase to transcribe their mRNA
73
Replication Cycle: Retroviruses
- Use a reverse transcriptase to copy their genomic sequence into DNA for insertion in the host chromosome
74
True or False. All animal viruses make proteins with host ribosomes.
True
| -Translation occurs in the cytoplasm
75
Assembly of new virions
- Capsid and genome
- May occur in the cytoplasm or nucleus
- Envelope proteins are inserted into a membrane
76
What happens when the release of progeny viruses from host cell happens?
- Lysis of cell
| - Budding
77
What happens during Budding?
- Virus passes through membrane
- Membrane lipids surround capsid to form envelope
- All enveloped viruses bud from a membrane
(plasma or organelle membrane)
78
What virus causes many human cancers?
- Oncogenic Viruses
79
What does an Oncogenic Virus do to the host cell?
- it transforms it to become cancerous
80
What are the mechanisms of oncogenesis?
- Insertion of an oncogene into the host genome
- Integration of the entire viral genome
- Expression of viral proteins that interfere with host cell cycle regulation
81
Entry of plant viruses into host cells usually requires.....
- mechanical transmission
82
What are the three routes that plant viruses enter?
- Contact with damaged tissues
- Transmission by an animal vector
- Transmission through seed
83
What prevents a lytic burst or budding out of virions in a plant?
- thick cell walls
84
Instead of this plant viruses are transmitted to uninfected cells by...
-plasmodesmata
85
What is plasmodesmata?
- Membrane channels that connect adjacent plant cells
| - Inner channel connects the ER
86
Since viruses are ubiquitous what are three defense mechanisms that animal and plants have?
- Genetic Resistance
- Immune System
- RNA interference (RNAi)
87
What is genetic resistance?
- Host continually experiences mutations
88
What is the immune system?
- "inactive immunity": interferons
| - "Adaptive immunity": antibodies
89
What is the RNA interference?
- Widespread among eukaryotes and archaea
90
What is the RNA interference?
- Widespread among eukaryotes and archaea
91
How does a "new" virus emerge to sicken humans?
1. As a result of human consumption of wildlife
| 2. As variants of endemic milder pathogens
92
What requires growth in host cells?
- Culturing Viruses
93
Bacteriophages may be cultured in....
- batch culture(in liquid)
| - isolated plaques on a bacterial lawn (on a plate)
94
What generates a step curve?
-Batch culture of viruses
95
What can be cultured within the whole organism by serial inoculation?
- Animal Viruses
96
What does serial inoculation ensure?
- that the virus strain maintains its original virulence, but the process is expensive and laborious
97
What is the alternative way to grown animal viruses?
- In human cell tissue culture
