Ch. 8 Flashcards
1
Q
Virus-
A
Genetic element that cannot replicate independently of a living (host) cell
2
Q
Virology-
A
The study of viruses
3
Q
Virus particle (virion)-
A
Extracellular form of a virus
- exists outside host and facilitates transmission from one host cell to another
- contains nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material
4
Q
Viral genomes-
A
- either DNA or DNA genomes
- some are circular, but most are linear
- only one type of genomic nucleic acid is found in the virion
5
Q
Viruses can be classified on the basis of what?
A
The hosts they infect
6
Q
Viral hosts and taxonomy:
A
- bacterial viruses (bacteriophages)
- archaeal viruses
- animal viruses
- plant viruses
- other viruses
7
Q
Smallpox virus
A
One of the larger viruses (about 200nm in diameter)
The size of the smallest known bacterial cell
8
Q
Poliovirus
A
One of the smallest viruses (28nm in diameter)
About the size of a ribosome
9
Q
Most viruses are ___ than prokaryotic cells.
A
Smaller
10
Q
Capsid-
A
The protein shell that surrounds the genome of a virus particle
11
Q
The capsid is composed of..
A
A number of protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid
12
Q
Capsomere-
A
Subunit of the capsid (individual protein molecules)
13
Q
What is the smallest morphological unit visible with an electron microscope?
A
Capsomere
14
Q
___ is a single-stranded RNA virus.
A
TMV
15
Q
TMV causes disease in ..
A
Tobacco, tomato, and related plants
16
Q
Nucleocapsid-
A
Complete complex of nucleic acid and protein packaged in the virion
17
Q
Enveloped virus-
A
Virus that contains additional layers around the nucleocapsid
18
Q
___ are constructed in highly symmetric ways.
A
Nucleocapsids
19
Q
Helical symmetry-
A
Rod-shaped viruses
20
Q
Length of virus is determined by..
A
Length of nucleic acid
21
Q
Width of virus determined by..
A
Size and packaging of protein subunits
22
Q
Icosahedral symmetry-
A
Spherical viruses
23
Q
Example of a virus with icosahedral symmetry
A
Human papilloma virus
24
Q
Human papilloma virus
A
Genital warts and cervical cancer
25
What is the most efficient arrangement of subunits in a closed shell?
Icosahedral symmetry
26
Enveloped virus-
Have membrane surrounding nucleocapsid
| - lipid bilayer with embedded proteins
27
___ makes initial contact with host cell.
Envelope
28
Envelope originates from host __ __.
Cytoplasmic membrane
29
Some virions contain enzymes critical to ___.
Infection
30
Lysozyme-
- makes hole in cell wall
- lyses bacterial cell
- bacteriophages
31
Neuraminidases-
- enzymes that cleave glycosidic bonds
- destroys animal cell connective tissue
- allows liberation of viruses from cell
32
Phases of viral replication:
- attachment (absorption)
- entry (penetration)
- synthesis
- assembly
- release
33
Phases of viral replication
Attachment (absorption) of..
The virus to a susceptible host cell
34
Phases of viral replication
Entry (penetration) of..
The virion or its nucleic acid
35
Phases of viral replication
Synthesis of..
Virus nucleic acid and protein by cell metabolism as redirected by virus
36
Phases of viral replication
Assembly of..
Capsids and packaging of viral genomes into new virions (maturation)
37
Phases of viral replication
Release of..
Mature virions from host cell
38
Virus replication is typically characterized by a ___ ___ ___.
One-step growth curve
39
Latent period-
Eclipse + maturation
40
Burst size
Number of virions released
41
How long do bacterial viruses take to replicate?
20-60 mins
42
How long do animal viruses take to replicate?
8-40 hours
43
___ replicate only in certain types of cells or in whole organisms.
Viruses
44
___ viruses are easiest to grow.
Bacterial
Model system
45
___ viruses can be cultivated in tissue or cell cultures.
Animal
46
___ viruses are typically most difficult because study often requires growth of the whole plant.
Plant viruses
47
Titer-
Number of infectious units per volume of fluid
48
Plaque assay-
Analogous to the bacterial colony; one way to measure virus infectivity
49
Plaques-
Clear zones that develop on lawns of host cells
50
___ ___ is used in quantitative virology.
Plating efficiency
51
Permissive cell-
Host cell that allows the complete replication cycle of a virus to occur
52
Bacteriophage T4
- virus of E. coli
| - one of the most complex penetration mechanisms
53
Restriction modification systems-
DNA destruction system
Effective only against double-stranded DNA viruses
54
Restriction enzymes-
Cleve DNA at specific sequences
55
Glycosylation-
Glucose attached to a hydroxyl
56
Methylation-
Addition of a methyl group
57
T4 genome can be divided into three parts:
Early proteins
Middle protein
Late proteins
58
Early and middle proteins:
Enzymes needed for DNA replication and transcription
59
Late proteins-
Head and tail proteins and enzymes required to liberate mature phase particles
60
Production of early proteins
- enzyme for the synthesis and glucosylation of the T4 base hydroxymethylcytosine
- enzymes that function in T4 replisome
- proteins that modify host rna polymerse
61
Production of middle proteins
Additional proteins that modify host rna polymerase
62
Production of late proteins
- synthesized later
- include proteins of virus coat
- typically structural components
- synthesized in larger amounts
63
Virulent mode-
Viruses lyse host cells after infection
64
Temperate mode-
Viruses replicate their genomes in tandem with host genome without killing the host
65
Temperate viruses-
Can undergo a stable genetic relationship within the host
66
Lysogeny-
State where most virus genes are not expressed and virus genome is replicated in synchrony with host chromosomes
67
Lysogen-
A bacterium containing a prophage
68
Packaging the T4 genome
- precursor of bacteriophage head is assembled
- packaging motor is assembled
- double-stranded DNA is pumped into head under pressure using ATP
- after head is filled with DNA, T4 tail, tail fibers, and other components are added
69
Bacteriophage lambda
- linear, dsDNA genome
| - complementary, single-stranded regions 12 nucleotides long at the 5' terminus of each strand
70
When it enters lytic pathway, lambda synthesizes long, linear concatemers of DNA by ___ ___ ___.
Rolling circle replication
71
Regulation of lytic vs lysogenic events in lambda is controlled by a complex ___ ____.
Genetic switch
72
cl protein (the lambda repressor)-
Causes repression of lambda lytic events
73
Cro repressor-
Controls activations of lytic events
74
Most phases contain ___ genomes.
dsDNA
75
Persistent infections-
Release of virions from host cell does not result in cell lysis
76
Latent infections-
Delay between infection by the virus and lytic events
77
Transformation-
Conversion of normal cell into tumor cell
78
Cell fusion-
Two or more cells become one cell with many nuclei
79
Retroviruses -
RNA viruses that replicate through a DNA intermediate
80
Gag-
Encode structural proteins
81
Pol-
Encode reverse transcriptase and integrase
82
Env-
Encode envelope proteins
83
Process of replication of a retrovirus:
- entrance into the cell
- removal of virion envelope at the membrane
- reverse transcription of one of the two RNA genomes
- integration of retroviral DNA info host genome
- transcription of retroviral DNA
- assembly and packaging of genomic RNA
- budding of enveloped virions; release from cell
84
About how many prokaryotes per ml of seawater?
10^6
85
About how many viruses per ml of seawater?
10^7
86
___ thought to have a major impact on evolution of bacteria.
Bacteriophages
87
Most of earths genetic diversity resides in ___.
Viruses
88
Most viruses are believed to be ___.
Bacteriophages
