Ch. 9 Flashcards
1
Q
Smallest s.s. DNA virus:
A
Circovirus 1.75 kilobase
2
Q
Largest d.s. DNA virus:
A
Megavirus 1.25 megabase pairs
3
Q
RNA viruses are typically ___ than DNA viruses.
A
Smaller
4
Q
Circovirus
A
Smallest s.s. DNA virus
1.75 kilobase
5
Q
Megavirus
A
Largest d.s. DNA virus
1.25 megabase pairs
6
Q
Viral genomes are either ___ or ___ genomes.
A
DNA or RNA
7
Q
Some viral genomes are circular, but most are ___.
A
Linear
8
Q
The Baltimore Scheme
A
Virus classification based on the relationship of the viral genome to its mRNA and recognizes seven classes of viruses
9
Q
What is the virus classification based on the relationship of the viral genome to its mRNA and recognizes seven classes of viruses?
A
The Baltimore scheme
10
Q
Single stranded genome can be either a ____ virus or ___ virus.
A
Positive-strand virus (plus-strand virus)
Negative-strand virus (minus-strand virus)
11
Q
Viral ___ is considered to be the plus strand.
A
mRNA
12
Q
Viral mRNA is considered to be the ___ strand.
A
Plus
13
Q
A phylogenetic tree has been constructed for ___ ___ ___ ___.
A
Nucleocytoplasmic large DNA viruses (NCLDV)
14
Q
Most viral genes from nature have unknown ___.
A
Function
15
Q
What bacteriophages contain single-stranded DNA genomes of the plus configuration?
A
Phi X174 and M13
16
Q
Phi X174 and M13
Transcription of the genome is proceeded by synthesis of a ..
A
Complementary strand of DNA
17
Q
Bacteriophage phi X174
A
- contains a circular single-stranded DNA genome inside an icosahedral virion
- very small genome with overlapping genes
- replication occurs via rolling circle replication
18
Q
How does replication occur in phi X174?
A
Rolling circle replication
19
Q
Bacteriophage M13
A
- model filamentous bacteriophage
- used as a cloning and DNA-sequencing vector in genetic engineering
- can be released without lysing host via a process called budding
- viral infection slows host growth
20
Q
___ is the model filamentous bacteriophage.
A
M13
21
Q
Bacteriophage ___ is used as a cloning and DNA-sequencing vector in genetic engineering.
A
M13
22
Q
Bacteriophage M13 can be released without lysing a host via a process called ___.
A
Budding
23
Q
Single-stranded DNA bacteriophages:
A
Phi X174 and M13
24
Q
Double-stranded DNA bacteriophages:
A
T7 and Mu
25
Bacteriophage T7
- infects E. coli
- virion has an icosahedral head and a very short tail
- genome always enters host cell in same orientation
- order of genes on the T7 chromosome influences regulation of virus replication
- DNA replication employs T7 DNA polymerase and involves terminal repeats and the formation of concatemers
26
Bacteriophage T7
Order of genes on the T7 chromosome influences regulation of ___ ___.
Virus replication
27
DNA replication employs T7 DNA polymerase and involves terminal repeats and the formation of ___.
Concatemers
28
Bacteriophage Mu
- "mutator" phage
- useful in bacterial genetics
- temperate phage
- replicates by transposition
- large virus with an icosahedral head, helical tail, and six tail fibers
- invertible G region of genome determines host range
- genome is integrated into the host
chromosome via a transposase
- in both lytic and lysogenic pathways, the genome is replicated as part of a large DNA molecule
- genome is packaged into the virion with short (5 bp) sequences of host DNA at either strand
29
"Mutator" phage
Induces mutations in host genome
30
Bacteriophage Mu replicates by ___.
Transposition
31
Bacteriophage Mu
Genome is integrated into the host chromosome via a ___.
Transposase
32
Bacteriophage Mu
Invertible G region of genome determines ___ ___.
Host range
33
Bacteriophage Mu
Lysogenic state requires sufficient amounts of a repressor protein to prevent transcription of ___ ___ ____.
Integrated Mu DNA
34
T4
Nucleic acid: dsDNA, linear
Structure: Icosahedral
Replication: concatemers; circular permutation; terminal repeats that are not identical
35
Lambda
Nucleic acid: dsDNA, linear
Structure: head & tail
Replication: rolling circle replication; temperate phage
36
Phi X174
Nucleic acid: ssDNA, circular
Structure: icosahedral
Replication: makes a replicative form; rolling circle replication
37
M13
Nucleic acid: ssDNA, circular
Structure: filamentous, helical
Replication: makes a replicative form; virions exit without lysis
38
T7
Nucleic acid: daDNA, linear
Structure: head & tail
Replication: concatemers, terminal repeats that are identical
39
Mu
Nucleic acid: dsDNA, linear
Structure: head & tail
Replication: temperate phage, transposase
40
Double-stranded DNA animal viruses that have unusual replication strategies:
Pox viruses
| Adenoviruses
41
Pox viruses - class I
- among the most complex and largest animal viruses known
- DNA replicates in the cytoplasm
- linear, double-stranded DNA virus
42
Pox viruses - class I
DNA replicates in the ___.
Cytoplasm
43
Adenoviruses - class I
- major group of icosahedral, linear, double-stranded DNA viruses
- cause mild respiratory infections in humans
- DNA replicates in the nucleus
44
Adenoviruses - class I
DNA replicates in the ___.
Nucleus
45
Replication requires protein primers and avoids synthesis of a ___ ___.
Lagging strand
46
Some DNA animal viruses can induce cancer:
Polyomavirus SV40
| Herpesviruses
47
Polyomavirus SV40 - class I
- induces tumors in animals
- noneveloped virion with an icosahedral head
- no enzymes in the virion; replicates in the host nucleus
- DNA is circular
- small genome, has overlapping genes
48
Polyomavirus SV40 - class I
Replicates in host ___.
Nucleus
49
In permissive host cells,...
Virus infection results in the formation of new virions and the lysis of the host cell
50
In nonpermissive host cells,...
The virus DNA becomes integrated into host DNA, genetically altering cells in the process
51
Herpesvirus - class I
- large group of viruses that cause diseases in humans and animals
- able to remain latent for extended periods of time
- an important group causes clinical forms of cancer
- infection follows attachment of virions to specific cell receptors
- three classes of mRNA are produced
52
Herpesvirus
Three classes of mRNA are produced:
Immediate early
Delayed early
Late
53
Immediate early
Encodes five regulatory proteins
54
Delayed early
Encodes DNA replication proteins
55
Late
Encodes structural proteins of the virus particle
56
Herpesvirus
An important group causes clinical forms of cancer:
- Epstein-Barr virus (mononucleosis)
| - Burkitt's lymphoma (cancer of the lymphatic system)
57
Poliovirus - class IV
- small virus
- host RNA and protein synthesis are inhibited when poliovirus replication begins
- paralytic vs. nonparalytic polio
58
In ___ viral RNA is translated directly, producing a single long, giant protein that undergoes self-cleavage to generate about 20 smaller proteins necessary for nucleic acid replication and virus assembly.
Poliovirus
59
Polyprotein
A single long, giant protein
60
___ polio can affect the spinal cord, the brain stem, or both.
Paralytic
61
FDR was paralyzed from the waist down due to what virus?
Poliovirus
62
Coronavirus - class IV
- larger virus
| - cause respiratory infections, including SARS, in humans and animals
63
SARS
Severe acute respiratory syndrome
64
Coronavirus virions
- are enveloped
| - contain club-shaped glycoprotein spikes on their surfaces
65
Negative-strand RNAs are complementary to the ___.
mRNA
66
Negative-strand RNA viruses
Only those that infect ___ are known.
Eukarya
67
Rhabdovirus - class V
Include viruses that cause:
- rabies in animals and humans
| - vesicular stomatitis in cattle, pigs, and horses
68
Rhabdovirus - class V
- enveloped viruses
| - virion is bullet-shaped
69
RNA of rhabdoviruses is transcribed in the host cytoplasm into two distinct classes:
1. Series of mRNAs encoding the structural genes of the virus
2. Positive-strand RNA that is a copy of the complete viral genome
70
Influenza - class V
- enveloped, pleomorphic virus
- segmented genome
- surface proteins interact with host cell surface
71
___ causes clumping of red blood cells.
Hemagglutinin
72
___ breaks down sialic acid component of host cytoplasmic membrane.
Neuraminidase
73
Processes that help influenza elude the host immune system:
- antigenic shift
| - antigenic drift
74
Antigenic shift
- portions of the RNA genome from two genetically distinct strains of virus infecting the same cell are reassorted
- generates virions that express a unique set of surface proteins
75
Antigenic drift
Structure of neuraminidase and hemagglutinin proteins are subtly altered
76
Reoviruses - class III
- nonenveloped nucleocapsid with a double shell of icosahedral symmetry
- virions contain virus-encoded enzymes necessary to synthesize mRNA and the new RNA genomes
- genome segmented into 10-12 molecules of linear double-stranded RNA
- replication occurs exclusively in host cytoplasm within the nucleocapsid
77
___ (RNA viruses) and ___ (DNA viruses) use reverse transcriptase for replication.
Retroviruses; hepadnaviruses
78
Retroviruses - class VI
- enveloped virions that contain two copies of the RNA genome
- virion contains several enzymes
- gene expression and protein processing are complex
79
Retroviruses
Virion contains several enzymes
Includes ___ ___ used to make DNA copy of genome.
Reverse transcriptase
80
All retroviruses have the three genes:
gag
pol
env
81
___ encodes several small viral structural proteins.
gag
82
___ is translated into a large polyprotein.
pol
83
The ___ product is processed into two distinct envelope proteins.
env
84
Hepadnaviruses - class VII
- virions small, irregular-shapes particles
- include hepatitis B
- viral replication occurs through an RNA intermediate
- unusual genomes (tiny)
85
Viroids -
Infectious RNA molecules that lack a protein coat
86
What are infectious RNA molecules that lack a protein coat?
Viroids
87
Viroids:
- smallest known pathogens
- cause a number of important plant diseases
- small, circular, ssRNA molecules
- do not encode proteins; completely dependent on host-encodes enzymes
88
What are the smallest known pathogens?
Viroids
89
Prions -
Infectious proteins whose extracellular form contains no nucleic acid
90
What are infectious proteins whose extracellular form contains no nucleic acid?
Prions
91
Prions:
- known to cause disease in animals
- host cell contains gene (PrnP) that encodes native form of prion protein that is found in healthy animals
- prion misfolding results in neurological symptoms of disease
92
Gene that encodes native form of prion protein that is found in healthy animals
PrnP
