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Flashcards in Chapter 5 Deck (196)
1

Viruses are a unique group of biological entities known to infect ____ type of cell, including bacteria, algae, fungi, protozoa, plants, and ___.

every
animals

2

___ water can contain about 10 million viruses per milliliter. Human feces probably contain ____ times that many.

sea
100

3

A variegated tulip gets its beautiful colors from a ___ infection.

viral

4

The French scientist Louis Pasteur was on the right track when he postulated that rabies was caused by a living thing smaller than ____, and in 1884 he was able to develop the first ____ for rabies.

bacteria
vaccine

5

Pasteur also proposed the term ____ to denote this special group of infectious agents.

virus

6

L. "poison"

virus

7

The first substantial revelations about the unique characteristics of viruses occurred in the _____.

1890s

8

D. Ivanovski and M. Beijerinick showed that a disease in ____ was caused by a virus. (tobacco mosaic virus)

tobacco

9

Friedrich Loeffler and Paul Frosh discovered an animal virus that causes ______ in cattle.

foot-and-mouth disease

10

Early researchers found that when infectious fluids from _____ were passed through porcelain filters deigned to trap bacteria, the filtrate remained _____. This result proved that an infection could be caused by a cell-free fluid containing agents smaller than bacteria and thus introduced the concept of ____.

host organisms
infectious
filterable virus

11

Years of experimentation were required to show that viruses were ____ particles with a definite size, shape, and chemical composition.

noncellular

12

Using special techniques, ___ can be cultured in laboratories.

viruses

13

Thanks to new genomic techniques, including ______ and "next-generation" nucleic acid sequencing techniques, we are getting a much clearer picture of the number and variety of viruses on earth.

DNA arrays

14

The ____ structure and behavior of viruses have led to debates about their connection to the rest of the microbial world.

unusual

15

One viewpoint holds that since viruses are unable to multiply independently from the ___, they are not living things but should be called infectious molecules.

host cells

16

Another viewpoint proposes that even though viruses do not exhibit most of the life processes of cells, they can direct them and thus are certainly more than inert and ____ molecules.

lifeless

17

This debate has greater philosphical than practical importance when discussing disease because viruses are agents of disease and must be dealt with through control, therapy, and _____, whether we regard them as living or not.

prevention

18

In keeping with their special position in the biological spectrum, it is best to describe viruses as either active or ____.

inactive

19

Recent discoveries suggest that viruses have been vital in forming ____ and other life forms as they are today.

cells

20

Scientists believe that approximately ___% of the human genome consists of sequences that come from viruses that have incorporated their genetic material ___ into human DNA.

10%
permanently

21

Bacterial DNA also contains ___% to ___% viral sequences.

10% to 20%

22

Viruses are different from their host cells in size, _____, and physiology.

behavior

23

Viruses are a type of obligate intracellular parasites that cannot multiply unless they invade a ____ and instruct its genetic an metabolic machinery to make and release quantities of new viruses.

specific host cell

24

Viruses are obligate intracellular parasites of bacteria, protozoa, fungi, algae, ____, and animals.

plants

25

It is estimated that virus particles makes up ___times the amount of prokaryotes on Earth's surface.

ten

26

Viruses are ubiquitous in nature and have a ___ on development of biological life.

major impact

27

Viruses are ultramicroscopic in size ranging from ____ nm up to ___ nm (diameter)

20 nm to 450 nm

28

Viruses are not ___; structure is very compact and economical.

cells

29

Viruses do not independently fulfill the characteristics of ___.

life

30

The basic structure of viruses consist of a ______ or (_____) surrounding nucleic acid core.

protein shell or capsid

31

The nucleic acid in viruses can be either DNA or RNA, but not _____.

both

32

The nucleic acid in viruses can be either DNA or RNA that is ____ or ____.

single stranded or double stranded

33

Molecules on virus surface impart _____ for attachment to host cells.

high specificity

34

Viruses multiply by taking control of host cell's _____ and regulating the synthesis and assembly of new viruses.

genetic material

35

Viruses lack ____ for most metabolic processes.

enzymes

36

Viruses lack machinery for synthesizing ___.

proteins

37

For many years, the animal viruses were classified mainly on the basis of their hosts and the kind of diseases they ___.

caused

38

Newer systems for naming viruses also take into account the actual ____ of the virus particles themselves, with only partial emphasis on ____ and disease.

nature
host

39

The main criteria presently used to group viruses are _____, chemical composition, and similarities in genetic make up.

structure

40

In 2012, the International Committee on the Taxonomy of viruses issued a report on the classification of viruses. The committee listed ___ orders with ____ families and 143gfenera, plus another 71 families with 278 genera not yet assigned to any order.

7
23

41

Previous to 2000, there had been only a ____ recognized order of viruses.

single

42

As a group, viruses represent the ____ infectious agents (with some unusual exceptions to be discussed later).

smallest

43

Viruses are dwarfed by their host cells: More than ____ bacterial viruses could fit into an average bacterial cell, and more than ___ million pollio viruses could be accommodated by an average human cell.

2000
50 million

44

Animal viruses range in size from the small ____ (around 20 nm) to the newly discovered _______, that are about the same size as common bacterial cell (1 um).

parvoviruses
pandoviruses

45

Some cylindrical viruses are relatively long (800 nm or .8um in length) but so narrow in diameter that their ____ is still limited without the high magnification and resolution of an electron microscope.

visibility

46

Viral architecture is most readily observed through special ___ in combination with electron microscopy.

stains

47

Viruses bear no real resemblance to ___, and that they lack any of the protein-synthesizing machinery found in even the simplest cells.

cells

48

Viruses molecular structure is composed of regular, repeating subunits that give rise to their _____ appearance.

crystalline

49

The general plan of virus organization is the utmost in simplicity and ___.

compactness

50

Viruses contain only those parts needed to invade and control a host cell: an ____ coating and a ____ containing one or more nuclei acid strands of either DNA or RNA, and sometimes one or two _____.

external
core
enzymes

51

All viruses have a protein ____, or shell, that surrounds the nucleic acid in the central core.

capsid

52

Together the capsid and the nucleic acid are referred to as the _________.

nucleocapsid

53

Members of 13 of the 20 families of animal viruses possess an additional covering external to the capsid called an _____, which is usually a modified piece of the host's cell membrane.

envelope

54

Viruses that consist of only a nucleocapsid are cconsidered ______.

naked viruses

55

Both naked and enveloped viruses possess proteins on their outer surfaces that project from either the _________ or ________.

nucleocapsid or the envelope

56

_____ are molecules that allow viruses to dock with their host cells and project from the outer surface of either a nucleocapsid or the envelope.

spikes

57

The enveloped viruses differ from naked viruses in the way that they enter and leave a _____.

host cell

58

A fully formed virus that is able to establish an infection in a host cell is often called a ___.

virion

59

The simplest virus is a ____.

naked virus

60

An envelope usually has special ____ inserted into it.

receptor spikes

61

When a virus particle is magnified several hundred thousand times the capsid appears as the most ______ feature.

prominent geometric

62

In general, each capsid is constructed from identical subunits called _____ that are constructed from protein molecules.

capsomers

63

The _____ spontaneously self-assemble into the finished capsid.

capsomers

64

Depending on how the capsomers are shaped and arranged, this assembly results in two different types: ____ and icosahedral.

helical

65

The simpler ____ capsids have rod-shaped capsomers that bond together to form a series of hollow discs resembling a bracelet. During the formation of the _____, these discs link with other discs to form a continuous helix into which the nucleic acid strand is ____.

helical
nucleocapsid
coiled

66

The nucelocapsids of _____ viruses are very rigid and tightly wound into a cylinder shaped package. An example is the tobacco mosaic virus, which attacks tobacco leaves (right).

naked helical

67

______ nucleocapsids are more flexible and tend to be arranged as a looser helix within the envelope. This type of morphology is found in several _____ human viruses, including influenza, measles, and rabies.

Enveloped
enveloped

68

These capsids form an ______ a three dimensional, 20 sided figure with 12 evenly spaced corners. The arrangement of the capsomers vary from one virus to another. Some viruses construct the capsid from a single type of capsomer, while others contain several types of capsomers.

icosahedron

69

____ is an example of a nake icosahedral virus.

Adenovirus

70

Two very common viruses, hepatitis B virus and the herpes simplex virus both possess ______.

enveloped icosahedrons

71

____, found in the viruses that infect bacteria , may have multiples types of proteins and take shapes that are not symmetrical. They are never enveloped.

complex capsids

72

When _____ (mostly animal) are released from the host cell, they take with them a bit of its membrane system in the form of an envelope.

enveloped viruses.

73

With enveloped viruses, some viruses bud off the cell membrane; others leave via the ______ or the endoplasmic reticulum.

nuclear envelope

74

Whichever avenue of escape, the viral ____ differs significantly from the host's membranes.

envelope

75

In the envelope, some or all of the regular membrane proteins are replaced with special _____.

viral proteins

76

Some of the envelope proteins attach to the capsid of the virus, and glcoproteins remain ____ on the outside of the envelope.

exposed

77

These protruding molecules, called ___ when they are on enveloped viruses, are essential for the attachment of viruses to the next host cell.

spikes

78

Because the envelope is more ____ than a capsid, enveloped viruses are pleomorphic (of variable shape) and range from spherical to filamentous in shape.

supple

79

The sum total of the genetic information carried by an organism is called its _____.

genome

80

Viruses, although neither alive nor cells, carry genetic information by ____.

nucleic acids

81

Unlike cells, which contain both DNA and RNA, viruses contain ____ DNA or RNA _____.

either
bot not both

82

Because viruses pack into a tiny space all of the genes necessary to instruct the host cell to make _____, the number of viral genes is quite small compared with that of a cell.

new viruses

83

Viruses posses only the genes needed to ____ host cells and redirect their activity.

invade

84

Bacteria and human cells have a much larger amount of genes which allow cells to carry out the complex _____ necessary for independent life.

metabolic activity

85

Antibiotics ____ work on viruses because antibiotics cannot alter functions or processes that do not exist in viruses. (no cytoplasmic membranes to attack or no protein synthesis)

do not

86

DNA viruses can have single stranded (ss) or double stranded (ds) DNA; the dsDNA can be arranged linerly or in ______.

ds circles

87

RNA viruses can be double stranded but are more often ____.

single-stranded

88

Single stranded RNA genomes that are ready for immediate translation into proteins are called _____.

positive sense RNA

89

Other RNA genomes have to be converted into the proper form to be made into proteins, and these are called _____.

negative sense RNA

90

RNA genomes may also be ____ meaning that the individual genes exist on separate pieces of RNA.

segmented

91

A special type of RNA virus is called a ____, these viruses are distinguished by the fact that they carry their own enzymes to create _____ out of their RNA.

retrovirus

92

Variola virus causes _____ and is a double stranded DNA virus.

smallpox

93

Herpes simplex II causes _____ and is a double stranded DNA virus.

genital herpes

94

Parvovirus causes ____ (skin condition) and is single stranded DNA.

erythema infection

95

Influenza virus causes ____ and is a single stranded (-) viruses.

influenza

96

Poliovirus causes ____ and is a single stranded (+) RNA virus.

poliomyelitis

97

Rotavirus causes _____ and is a double stranded RNA.

gastroenteritis

98

HIV causes ___ and is a single stranded RNA reverse transcriptase.

AIDS

99

In all cases, these tiny strands of genetic material carry the blueprint for viral _____ and ______.

structure and functions

100

Basically, viruses are genetic parasites because they cannot multiply until their nucleic acid has reached the ____ of the host cell. At the minimum they must carry genes for synthesizing the ___ and genetic material, for regulating the actions of the host and the packaging of the mature virus.

internal habitat
viral capsid

101

In addition to the protein of capsid, the proteins and lipids of the envelopes, and the nucleic acid of the core, viruses can contain _______ for specific operations within their host cells.

enzymes

102

Viruses may come with preformed enzymes that are required for _____.

viral replication

103

Examples of preformed enzymes include _____ that synthesize DNA and RNA, and the replicases that copy RNA.

polymerases

104

The AIDS virus comes equipped with _____ for snythesizing DNA from RNA.

reverse transcriptase

105

Viruses completely lack the genes for synthesis of _____ enzymes. This deficiency has little consequence, because viruses have adapted to completely take over their hosts' ____ resources.

metabolic
metabolic

106

Some viruses can actually carry away ___ from their host cell. Like arenaviruses that pack along host ribosomes, and retroviruses that ____ the host's tRNA molecules.

substances
borrow

107

The process of viral _______ is an extraordinary biological phenomenon. The nature of this cycle dictates the way the virus is _____ and what it does to its host, the responses of the immune defenses, and human measures to control viral infections

multiplication
transmitted

108

Viruses are minute ____ that seize control of the synthetic and genetic machinery of cells.

parasites

109

The phases of the life cycle of animal viruses are

adsorption
penetration and uncoating
synthesis
assembly
release from the host cell

110

The length of the entire multiplication cycle varies from 8 hours in polioviruses to ___ hours in some herpesviruses.

36 hours

111

Because a virus can invade its host cell only through making an exact fit with a specific host molecule, the range of hosts it can infect is _____. This is known as the ____.

limited
host range

112

The host range, may be highly restricted as in the case of ____, which infects only liver cells of humans; moderately restrictive like the poliovirus, which infects intestinal and ___ cells of primates (humans, apes, monkeys); or broad like the rabies virus, which can infect various cells of all mammals.

hepatitis B
nerve

113

Cells that lack compatible virus ____ are resistant to absorption and invasion by that virus.

receptors

114

This ____ explains why human liver cells are not infected by the canine hepatitis virus and dog liver cells cannot hos the human hepatitis A virus.

host range

115

The host range also explains why viruses usually have ___ specificities called tropisms for certain cells in the body. The hepatitis B virus targets the liver, and the mumps virus targets the salivary glands.

tissue

116

The configuration of the spike s on viruses have a complementary fit for ____. This process in which the virus lands on the cell and plugs into receptors is termed ____.

cell receptors
docking

117

Animal viruses exhibit some impressive mechanisms for entering a host cell. The flexible cell membrane of the host is penetrated by the ___ or its ____.

whole virus
nucleic acids

118

In penetration by _____, the entire virus is engulfed by the cell and enclosed in a vacuole or vesicle. When enzymes in the vacuole dissolve the envelope and capsid, the virus is said to be ____.

endocytosis
uncoated

119

___ is a process that releases the viral nucleic acid.

uncoating

120

The exact manner of uncoating varies, but in most cases, the virus fuses with the wall of the ____. Another means of entry involves direct fusion of the ____ with the host membrane (in influenza and mumps).

vesicles
viral envelope

121

When the viral envelope is fused directly during uncoating, the envelope merges directly with the cell membrane, thereby liberating the ______ into the cell's interior.

nucleocapsid

122

In general, the DNA viruses (except poxviruses) enter the host cell's ____. and are replicated and assembled there. With few exceptions (such as retroviruses), RNA viruses are replicated and assembled in the ____.

nucleus
cytoplasm

123

The synthesis of new genomes and mRNAs for translation differ among the various types of RNA and ____.

DNA viruses

124

The retroviruses turn their RNA genomes into ____. This step is accomplished by a viral enzyme called _____ and has important implications in infections with these viruses, one of which is HIV.

DNA
reverse transcriptase

125

In the life cycle of dsDNA viruses, the synthesis phase is divided into two parts. During the early phase, viral DNA enters the ___, where several genes are transcribed into a messenger RNA. The newly synthesized RNA transcript then moves into the cytoplasm to be translated into ____ (enzymes) needed to replicate the viral DNA; this replication occurs in the nucleus. The host's own DNA polymerase is often involved, though some viruses (herpes) have their own. During the late phase, other parts of the viral genome are transcribed and translated into proteins required to form the capsid and ___. The new viral genomes and capsids are assembled, and the mature viruses are released by budding or cell deginteration. In some viruses, the viral DNA becomes silently integrated into the host's genome by ___ at a particular site on the host genome. This integration may later lead to the transformation of the host cell into a cancer cell and the production of a tumor.

nucleus
viral proteins
other structures
integration

126

____, this step actually puts together the new viruses using the "parts" manufactured in the synthesis process: new capsid and new nucleic acids.

assembly

127

___ is the viral release from the host cells.

release

128

The number of viruses released by infected cells is ____, controlled b factors such as size of the virus and health of the host cell.

variable

129

About 3,000 to 4,000 virions are released from a single cell infected with poxviruses, whereas a poliovirus-infected cell can release over ____ virions.

100,000

130

If even a small number of these virions happen to meet another susceptible cell and infect it, the potential for rapid viral proliferation is ____.

immense.

131

____ effects are defined as virus-induced damage to the cell that alters its microscopic appearance.

cytopathic effects

132

Individual cells can undergo gross changes in shape or size, or develop ____ changes due to viruses.

intracellular

133

It is common to find _____, or compacted masses of viruses or damaged cell organelles, in the nucleus and cytoplasm.

inclusion bodies

134

Examination of cells and tissues for cytopathic effects is an important part of the ____ of viral infections.

diagnosis

135

One very common CPE (cytopathic effect) is the fusion of multiple ___ into single large cells containing multiple nuclei. These ____ are a result of some viruses ability to fuse membranes. The respiratory virus, syncytial virus is even named for this effect.

host cells
syncytia

136

Accumulated damage from a virus infection kills most host cells, some cells maintain a carrier relationship, in which the cell harbors the virus and is not immediately lysed. These so called _____ infections can last from a few weeks to teh remainder of teh host's life.

persistent infections

137

Viruses can remain latent in the cytoplasm of a host cell, or can incorporate into the ___ of a host.

DNA

138

When viral DNA is incorporated into the DNA of teh host, it is called a ____.

provirus

139

One provirus, the measles virus, can remain hidden in brain cells for many years, causing progressive damage and ____.

loss of function

140

Several types of viruses remain in a _______ state, periodically becoming reactivated. Examples include herpes simplex virus (cold sores and genital herpes) and herpes zoster virus (chickenpox and shingles). Both viruses can go into latency in ____ cells and later emerge under the influence of various stimuli to cause recurrent symptoms.

chronic latent
nerve

141

Some animal viruses enter a host cell and permanently alter it genetic material, leading to ____.

cancer.

142

Experts estimate that up to ___% of human cancers are caused by viruses. These viruses are termed oncogenic, and tehir effect on the cell is called ____.

20%
tranformation

143

In microbial genetics, the transfer of genetic material contained in "naked" DNA fragments from a donor cell to a competent recipient cell.

transformation

144

Viruses that cause cancer in animals can act in several different ways. The virus can carry genes that directly cause the cancer. In some other cases, the virus produces proteins that induce a loss of _____ in the cell, leading to cancer.

growth regulation

145

Transformed cells have an increased rate of growth; alterations in chromosomes, changes in the cell's ____; and the capacity to divide for an indefinite period, unlike normal animal cells.

surface molecules

146

Mammalian viruses capable of initiating tumors are called ____.

oncoviruses

147

Some oncoviruses are ____ viruses such as papillomavirus (genital warts associated with cerival cancer), herpesviruses (epstein-barr virus, and hepatitis B virus (liver cancer).

DNA

148

A virus related to HIV - HTLV I is also involved in ____. These finding have spurred a great deal of speculation on the possible involvement of viruses in cancers and other diseases such as multiple sclerosis.

human cancers

149

A virus that specifically infects bacteria.

bacteriophage

150

Fredrick Twort and Felix d'Herelle discovered bacterial viruses in 1915, it first appeared that the bacterial host cells were being eaten by some unseen parasite; hence the name _____.

bacteriophage

151

Most bacteriophages contain ____ DNA, although _____ DNA and RNA types exist as well.

double stranded DNA
single stranded DNA

152

Every bacterial species is parasitized by various ____ bacteriophages.

specific

153

Bacteriophages are of great interest to medical microbiologists because they often make the bacteria they infect more _____ for humans.

pathogenic

154

The most widely studied bacteriophages are those of the intestinal bacterial ______ especially the ones known as the T-even phages such as T2 and T4. They have an icosahedral capsid head containing DNA, a central tube (surrounded by a sheath), collar,, base plate, tail pins and fibers, which in combination make an efficient package for infecting a bacterial cell.

Escherichia coli

155

T-even bacteriophages go through similar stages as the ____ viruses.

animal

156

T-even bacteriophages ____ to host bacteria using specific receptors on the bacterial surface. Although the entire phage does not enter the host cell, the nucleic acid penetrates the host after being injected through a rigid tube the phage inserts through the _____ and wall. This eliminates the need for uncoating. Entry of the nucleic acid causes the cessation of host cell DNA replication and protein syntheis. Soon the host cell machinery is used for viral ____ and synthesis of viral proteins. As the host cell produces new phage parts, the parts spontaneously ____ to bacteriophages.

adsorb
bacterial membrane
replication
assemble

157

An average size Escherichia coli cell can contain up to 200 new phage units at the end of the assembly period. Eventually, the host cell becomes so packed with viruses that it ____ thereby releasing the mature virions. This process is hastened by viral enzymes produced late in the infection cycle that digest the ____, thereby weakening it. Upon release, the virulent phages can spread to other susceptible bacterial cells and begin a new cycle of infection.

lyses - splits open
cell envelope

158

Bacteriophage infection may result in lysis of the cell. When this happens it is said that the bacteriophage has been in the ____ phase or cycle.

lytic

159

Alternatively, bacteriophages can be less obviously damaging, in a cycle called the _____ cycle.

lysogenic

160

In 2008, a new type of virus was discovered, _____. They parasitize other viruses that are infecting the same host cell they infect, using genes from other (usually larger) viruses for their own replication and production. Even though these are parasites of viruses, note that they must be in a ___, along with their host virus.

virophages
host cell

161

While special DNA phages, called ____ phages, can participate in a lytic phase, they also have the ability to undergo adsorption and penetration into the bacterial host and not undergo replication or release immediately. Instead, the viral DNA enters an inactive _____ state, reminiscent of the provirus state in animal viruses, during which it is inserted into the bacterial chromosome. This viral DNA will be retained by teh bacterial cell and copied during its normal cell division so that they cell's progeny will also have the temperate phage DNA.

temperate phages
prophage state

162

This condition, in which the host chromosome carries bacteriophage DNA, is termed _____ because viral particles are not produces, the bacterial cells carrying temperate phages do not lyse and they appear entirely normal.

lysogeny

163

On occasion, in a process called ____, the prophage in a lysogenic cell will be activated and progress directly into viral replication and the lytic cells.

induction

164

Lysogeny is a less deadly form of parasitism than the full _____ and is though to be an advancement that allows the virus to spread without killing the host.

lytic cycle

165

Bacteriophages are just now receiving their due as important ___ of biological life.

shapers

166

Scientist believe that there are more bacteriophages than ____ forms of life in the biosphere combined.

all other

167

Viral genes linger in human, animal, plant, and bacterial genomes in huge numbers. As such, viruses can contribute what are essentially ____ traits to the bacteria, so much so that it could be said that all bacteria-indeed all organisms are really hybrids of themselves and the viruses that infect them.

permanent

168

Many bacteria that infect humans are lysogenized by ______. Occasionally bacteriophage genes in the bacterial chromosome cause the production of toxins or _____that cause pathology in the human.

bacteriophages
enzymes

169

When a bacterium acquires a new trait from its temperate phage, it is called _____. The phenomenon was first discovered in the 1950s in the bacterium that causes diptheria, Corynebacterium diptheriae. The diphtheria toxin responsible for the deadly nature of the disease is a bacteriophage product.

lysogenic conversion

170

Scientists have developed methods, which include inoculation of lab-bred animals and embryonic bird tissues and cell _____.

culture methods

171

The primary purposes of viral cultivation are to _______ and _______ viruses in clinical specimens, prepare viruses for vaccines, and do detailed research on viral structure, multiplication cycles, genetics, and ______.

isolate and identify
effects on host cells

172

Specially bred strains of white mice, rats, hamsters, guinea pigs, and rabbits are the usual choices for ____ cultivation of viruses.

animal

173

Invertebrates (insects) or nonhuman primates are occasionally used for animal ____.

cultivation

174

Because viruses can exhibit host specificity, certain animals can propagate a given virus more ____ than others.

readily

175

A bird egg containing an embryo provides an _____ and self-supporting unit, complete with its own sterile environment and nourishment. It also furnishes several embryonic tissues that readily support ____. Chicken, duck, and turkey eggs are the most common choices for inoculation. The virus must be injected through the egg shell, usually by drilling a hole or making a small window.

intact
viral multiplication

176

The most important early discovery that led to easier cultivation of viruses in the lab was the development of a simple and effective way to grow populations of isolated animal cells in culture. These type of ____ cultivation systems are termed cell culture, or tissue culture.

in vitro

177

Animal cell cultures are grown in sterile chambers with special media that contain the correct nutrients required by animal cells to survive. The cultured cells grow in the form of a ____, a single confluent sheet of cells that supports viral multiplication and permits close inspection of the culture for signs of ___.

monolayer
infection

178

For the first time in 2012, the FDA approved for general use a cell culture based vaccine for the seasonal ____.

influenza virus

179

One way to detect the growth of a virus in culture is to observe ____ and lysis of infected cells in the monolayer of cells.

degeneration

180

The areas where virus-infected cells have been destroyed show up as __, well defined patches in the cell sheet called plaques.

clear

181

_____ are essentially the macroscopic manifestation of cytopathic effects (CPEs).

plaques

182

The same technique is used to detect and count bacteriophages, because they also produce ____ when grown in soft agar cultures of their host cells (bacteria). These develop when the viruses released by an infected host cell radiate out to adjacent host cells. As new cells become infected, they die and release more viruses, and so on. As the process continues, teh infection spreads, gradually and ____ from teh original point of infection, causing the macroscopic appearance of round, clear spaces that correspond to areas of dead cells.

plaques
symmetrical

183

Not all noncellular infectious agents are ___.

viruses.

184

One group of unusual forms even smaller and simpler than viruses, is implicated in chronic, persistent disease in humans and animals. These diseases are called ____because the brain tissue removed from affected animals resembles a sponge. This infection has a long period of latency (usually several ___) before the first clinical signs appear. Signs range from mental derrangement to loss of _____. The disease are progressive and universally fatal.

spongiform encephalopathies
years
muscle control

185

A common feature of spongiform encephalopathy is the deposition of distinct protein fibrils in the _____.

brain tissue

186

Researchers have hypothesized that these fibrils are the agents of the disease (spongiform encephalopathy) and have named them ______.

prions

187

Creutzfeldt-Jakob disease afflicts the central nervous system of humans and causes gradual degeneration and ____.

death - spongiform encephalopothy

188

Bovine spongiform encephalophathy (BSE) or ________ was recently the subject of fears and a crisis in Europe when researchers found evidence that the disease could be acquired by humans who consumed contaminated beef. This was the first incidence of prion disease transmission from animals to humans.

mad cow disease

189

Several hundred Europeans developed symptoms of a variant form of Creutzfeldt jakob disease, leading to strickt controls on exporting _____ and ____ products.

cattle and beef

190

Prions are composed primarily of ____ and no nucleic acids.

proteins

191

_____ viruses are actually dependent on other viruses for replication.

satellite viruses

192

Th adeno-associated virus (AAV) is an example of a _____ virus because i can infect cells that are infected with other viruses or that have had their DNA disrupted through other means.

satellite virus

193

The delta agent, is a naked circle of RNA that is expressed only in the presence of hpe B anc can worsen the severity of liver damage is an example of a ____.

satellite virus

194

Plants are also parasitized by viruslike agents called _____ that differ from ordinary viruses by being very small (about one tenth the size of an average virus and being composed of only naked strands of RNA, lacking a capis or any other type of coating.

viroids

195

Viroids are significant pathogens in several _____ important plants, including tomatoes, potatoes, cucumbers, citrus tress, and chrysanthemums.

economically

196

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