Chapter 6 - The Search for the Elusive Virus Flashcards
1
Q
Who postulated that rabies was caused by a virus (1884)
A
Louis Pasteur
2
Q
Who showed a disease in tobacco was caused by a virus (1890s)
A
Ivanovski and Beijerinck
3
Q
1950s ________ was a multifaceted discipline
A
Virology
4
Q
Noncellular particles with a definite size, shape, and chemical composition
A
Viruses
5
Q
There is no universal agreement on how and when _______ originated
A
Viruses
6
Q
Viruses are considered the ____ ________ microbes on earth
A
Most abundant
7
Q
Viruses played a role in _________of Bacteria, Archaea, and Eukarya
A
Evolution
8
Q
Viruses are ________ ____________ parasites
A
Obligate intracellular
9
Q
Most viruses are less than _____
A
0.2 μm
10
Q
Viruses require an ________ __________ to see
A
Electron microscope
11
Q
Viruses bear no resemblance to _____
A
Cells
12
Q
Viruses lack _______ ____________ machinery
A
Protein-synthesizing
13
Q
Viruses contain only the parts needed to ______ and _______ a host cell
A
Invade and control
14
Q
All viruses have _______
A
Capsids
15
Q
Protein coats that enclose and protect their nucleic acid
A
Capsids
16
Q
The capsid together with the nucleic acid is the:
A
Nucleocapsid
17
Q
Some viruses have an external covering called the:
A
Envelope
18
Q
Those lacking an envelope are
A
Naked
19
Q
Each capsid is constructed from identical subunits called:
A
Capsomers
20
Q
What are capsomers made of?
A
Protein
21
Q
What are the two structural types of viruses?
A
- Helical
2. Icosahedral
22
Q
Continuous helix of capsomers forming a cylindrical nucleocapsid
A
Helical
23
Q
- 20-sided with 12 corners
- Vary in the number of capsomers
- Each capsomer may be made of 1 or several proteins
- Some are enveloped
A
Icosahedral
24
Q
- Mostly animal viruses
- Acquired when the virus leaves the host cell
- Exposed proteins on the outside of the envelope, called spikes, essential for attachment of the virus to the host cell
A
Viral envelope
25
- Protects the nucleic acid when the virus is outside the host cell
- Helps the virus to bind to a cell surface and assists the penetration of the viral DNA or RNA into a suitable host cell
Capsid/Envelope
26
Complex viruses
Atypical viruses
27
- Poxviruses lack a typical capsid and are covered by a dense layer of lipoproteins
- Some bacteriophages have a polyhedral nucleocapsid along with a helical tail and attachment fibers
Complex viruses: atypical viruses
28
Either DNA or RNA but never both
Viral genome
29
Carries genes necessary to invade host cell and redirect cell’s activity to make new viruses
Nucleic Acids
30
Number of genes varies for each type of virus - ___ to ________
Few to hundreds
31
__________ enzymes may be present
Pre-formed
32
DNA or RNA
Polymerases
33
Copy RNA
Replicases
34
Synthesis of DNA from RNA (AIDS virus)
Reverse transcriptase
35
Main criteria presently used for viruses are _________, ________ ___________, and _______ ______
Structure, chemical composition, and genetic makeup
36
How many orders are there of viruses?
3
37
How many families are there of viruses?
63
38
How many genera are there of viruses?
263
39
Family name of viruses ends in:
viridae
| - ex: Herpesviridae
40
Genus name of viruses ends in:
virus
| - ex: Simplexvirus
41
General phases in animal virus multiplication cycle
1. Adsorption
2. Penetration
3. Uncoating
4. Synthesis
5. Assembly
6. Release
42
What is host range?
Spectrum of cells a virus can infect
43
Flexible cell membrane is penetrated by the whole virus or its nucleic acid by:
- Endocytosis
| - Fusion
44
Entire virus is engulfed and enclosed in a vacuole or vesicle
Endocytosis
45
Envelope merges directly with membrane resulting in nucleocapsid’s entry into cytoplasm
Fusion
46
DNA viruses generally are replicated and assembled in the _______
Neculeus
47
RNA viruses are generally replicated and assembled in the _________
Cytoplasm
48
Positive-sense RNA contain the message for ___________
Translation
49
Negative-sense RNA must be converted into ________ _____ _______
Positive-sense message
50
Assembled viruses leave host cell in one of two ways:
Budding or lysis
51
Exocytosis; nucleocapsid binds to membrane which pinches off and sheds the viruses gradually; cell is not immediately destroyed
Budding
52
Nonenveloped and complex viruses released when cell dies and ruptures
Lysis
53
Number of viruses released is variable
3,000-4,000 released by _______
>100,000 released by __________
- Poxvirus
| - Poilovirus
54
Virus-induced damage to cells
Cytopathic effects
55
What are cytopathic effects?
1. Changes in size and shape
2. Inclusion bodies
3. Cells fuse to form multinucleated cells
4. Cell lysis
5. Alter DNA
6. Transform cells into cancerous cells
56
Cell harbors the virus and is not immediately lysed
Persistent infections
57
Can last weeks or host’s lifetime; several can become reactivated periodically
Chronic latent state
58
Some animal viruses enter host cell and permanently alter its genetic material resulting in cancer. What is this called?
Transformation of the cell
59
Transformed cells have increased rate of growth, alterations in chromosomes, and capacity to divide for indefinite time periods resulting in ______
Tumors
60
Mammalian viruses capable of initiating tumors are called ___________
Oncoviruses
61
Papillomavirus
Cervical cancer
62
Epstein-Barr virus
Burkitt’s lymphoma
63
Bacterial viruses (phages)
Bacteriophages
64
Most widely studied are those that infect ___________ ____ - complex structure, DNA
Escherichia coli
65
Multiplication goes through similar stages as animal viruses but _________ of nucleic acid upon entry into the host is not necessary
Uncoating
66
Release is a result of cell lysis induced by viral enzymes and accumulation of viruses
Lytic cycle
67
What are the 6 steps in phage replication?
1. Adsorption
2. Penetration
3. Replication
4. Assembly
5. Maturation
6. Release
68
Results in the spread of the virus without killing the host cell
Lysogeny
69
Phage genes in the bacterial chromosome can cause the production of toxins or enzymes that cause pathology
Lysogenic conversion
70
What are temperate phages?
- Prophage
- Lysogeny
- Induction
71
Obligate intracellular parasites that require appropriate cells to replicate
Animal viruses
72
What are the methods used to identify animal viruses?
- Cell (tissue) cultures
- Bird embryos
- Live animal inoculation
73
Viruses are the most common cause of _____ __________
Acute infections
74
There are several _______ viral infections per year
Billion
75
Some viruses have high _________ rates
Mortality
76
There are possible connections of viruses to _______ ____________ of unknown cause
Chronic afflictions
77
Viruses are major participants in the earth’s _________
Ecosystem
78
Misfolded proteins, contain no nucleic acid
Prions
79
Extremely resistant to usual sterilization techniques
Prions
80
- Cause transmissible spongiform encephalopathies – fatal neurodegenerative diseases
- Common in animals
Prions
81
Dependent on other viruses for replication
Satellite viruses
82
Replicates only in cells infected with adenovirus
Adeno-associated virus
83
Naked strand of RNA expressed only in the presence of hepatitis B virus
Delta agent
84
Short pieces of RNA, no protein coat; only been identified in plants
Viroids
