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Microbiology LFS 261 > Lecture 12 > Flashcards

Lecture 12 Flashcards

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1
Q

Genetic elements that can replicate independently of a host cell’s chromosomes but not independently of a host cell themselves.

A

Viruses

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2
Q

In order to multiply, viruses must enter into a cell in which they can replicate. Such a cell is called a ______.

A

host.

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3
Q

When a virus genome is introduced into a host cell and reproduces, the process is called ________

A

infection

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4
Q

The virus redirects preexisting host machinery and metabolic functions necessary for virus replication and the assembly of new _______.

A

virions.

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5
Q

The total genetic material within the cell is referred to as a what?

A

Genome

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6
Q

A fully formed virus particle is referred to as what?

A

viron

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7
Q

Viruses can also be classified on the basis of the host they infect. What are 3 examples of this?

A

Animal viruses Plant viruses Bacterial viruses (bacteriophages)

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8
Q

This word comes from Greek phagein meaning “to eat”.

A

Phage. They have been studied primarily as convenient model systems for research on the molecular biology and genetics of virus reproduction.

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9
Q

Many of the basic concepts of virology were first worked out with _______ ________ and subsequently applied to viruses of higher organisms.

A

bacterial viruses

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10
Q

Virus particles (virions) vary widely in size and shape. The nucleic acid of a virus is surrounded by a protein coat called _______.

A

capsid

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11
Q

Each capsid is composed of protein subunits called _________.

A

capsomeres. The arrangement of capsomeres is characteristic of a particular type of virus.

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12
Q

In some viruses, the capsid is covered by an envelope, which usually consists of some combination of what 3 things?

A

lipids, proteins, and carbohydrates.

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13
Q

Depending on the virus, envelopes may or may not be covered by _______.

A

spikes

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14
Q

When the host has been infected by a virus, the host immune system is stimulated to produce _________.

A

antibodies

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15
Q

How can viruses like influenza escape antibodies and infect the same person again?

A

Regions of the genes that code for these viruses’ surface proteins are susceptible to mutations.

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16
Q

Viruses may be classified into several different morphological types on the basis of their capsid architecture, which is studied using a TEM or a technique called X-ray crystallography. List 4 of these.

A

Helical viruses, polyhedral viruses, enveloped viruses, complex viruses

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17
Q

The viral nucleic acid is found within a hollow cylindrical capsid that has a helical structure. Viruses that cause rabies and Ebola Hemorrhagic Fever

A

Helical viruses

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18
Q

Many animal, plant and bacterial viruses are polyhedral, or many-sided viruses. The capsid of most polyhedral viruses is in the shape of an __________, a regular polyhedron with ________ triangular faces and _______ corners such as polio-virus.

A

icosahedron, 20, 12

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19
Q

Enveloped viruses are roughly what shape?

A

spherical

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20
Q

When helical or polyhedral viruses are enclosed by envelopes, they are called what?

A

enveloped helical or enveloped polyhedral viruses.

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21
Q

Example of enveloped helical virus

A

influenzavirus

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22
Q

Example of enveloped polyhedral viruses

A

herpes simplex virus

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23
Q

Virologists began addressing the problem of viral taxonomy in 1966 with the formation of what committee?

A

ICTV - International Committee on the Taxonomy of Viruses

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24
Q

the ICTV has been grouping viruses into families based on what 3 things?

A

1] Nucleic acid type 2] Strategy for replication

3] Morphology

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25
Q

The suffix -virus is used for the _______ names

A

genus

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26
Q

Virus Family names end in -_______

A

viridae

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27
Q

Virus Order names end in -________

A

ales

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28
Q

This is a group of viruses sharing the same genetic information and ecological niche.

A

virus species

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29
Q

Specific epithets for viruses are not used. Thus, viral species are designated by descriptive common names, such as HIV, with subspecies designated by a number HIV-1

A

FYI

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30
Q

Viruses must be maintained within _____ _____ in order to multiply. This complicates their detection, enumeration, and identification

A

living cells or host cell

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31
Q

What are the Three methods are commonly used for culturing animal viruses?

A
  1. Living animals
  2. Embryonated eggs
  3. Cell cultures
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32
Q

In 1986, simian AIDS, an immune deficiency disease of green monkeys, was reported, and followed in 1987 by feline AIDS, an immune deficiency disease of domestic cats. These diseases are caused by _______ , which are closely related to HIV, and the disease develops within few months, thus providing a model for studying viral growth in different tissues

A

lentiviruses.

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33
Q

In 1990, a way to infect mice with human AIDS was found when immuno-deficient mice were grafted to produce human _______ and human _______. The mice provide a reliable model for studying viral replication, although they do not provide models for vaccine development.

A

T cells, gamma globulin.

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34
Q

Viral growth is signaled by what 3 things?

A

Death of the embryo
Embryo cell damage
By the formation of typical pocks or lesions on the egg membrane

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35
Q

What has replaced embryonated eggs as the preferred type of growth medium for many viruses.

A

cell cultures (Because these cultures can be propagated and handled much like bacterial cultures, they are more convenient to work with than whole animals or embryonated eggs.)

36
Q

Cell cultures consist of cells grown in _____ _______ in the laboratory.

A

culture media

37
Q

Viruses can be grown in what two types of cell lines.

A

primary or continuous

38
Q

What type of cell line derives from tissue slices, tend to die out after only a few generations

A

Primary cell lines

39
Q

What type of cell lines are transformed (cancerous) cells that can be maintained through an indefinite number of generations

A

continuous cell lines

40
Q

The cell culture technique became practical after the discovery of __________, as the cells have to be maintained microbial free.

A

antibiotics

41
Q

Viruses that use bacterial cells as a host

A

bacteriophages

42
Q

much of our understanding of viral multiplication has come from _________

A

bacteriophages.

43
Q

They can be grown either in suspensions of bacteria in liquid media or in bacterial cultures on solid media. The use of solid media makes possible the ________ for detecting and counting viruses.

A

plaque method

44
Q

Concentration of a viral suspensions measured by the number of plaques called _______ _______ _______

A

plaque-forming units.

45
Q

The best understood viral life cycles are those of bacteriophages
Phages can multiply by two alternative mechanisms:

A

Lytic cycle and Lysogenic cycle

46
Q

What phage multiplication mechanism end with lysis and death of the host cell?

A

Lytic cycle

47
Q

In what phage multiplication mechanism does the host remain alive?

A

lysogenic cycle

48
Q

The first step in reproduction of a bacteriophage is __________

A

adsorption (attachment)

49
Q

In the first step in reproduction of a bacteriophage what becomes attached to the cell wall?

A

The tip of the phage tail

50
Q

Since available evidence indicates that both phage and host cell carry a net charge, a certain concentration of _______ will allow the phage and the cell to approach close enough for adsorption to occur. Studies have shown that the actual penetration is mechanical, but it may be facilitated by a ______ _______which is carried on the tail of the phage.

A

cations, “phage lysozyme”

51
Q

Penetration is achieved when what three things occur?

A

1] The tail fibres of the virus attach to the virion and hold it firmly against the cell wall
2] The tail sheath contracts, driving the core of the tube in the virus tail into the cell
3] Injecting the DNA much as a syringe injects a vaccine

52
Q

The protein coat, which forms the capsule head, and the tail structure of the virus remain as ghosts outside the cell. The virus material entering the cell is almost entirely _____ or _____, which carries the information necessary for the synthesis of new virus particles.

A

DNA or RNA

53
Q

Immediately after injection of the virus DNA or RNA into the host cell, the virus takes charge of the host’s metabolic machinery, causing it to manufacture virus ______ _____ rather than bacterial _____ _____

A

nucleic acids, nucleic acids.

54
Q

About _____ minutes after initial infection, some ______ new bacteriophages will have been assembled, and the bacterial cell bursts, releasing the new phage to infect other bacteria and begin the cycle over again.

A

25, 200

55
Q

The time that elapses from phage attachment to release is known as _____ _____and averages 20-40 minutes.

A

burst time

56
Q

The number of newly synthesized phage particles released from a single cell is referred to as ______ _____ and usually ranges from about 50 to 200.

A

burst size

57
Q

The various stages involved in the multiplication of phages can be demonstrated experimentally in what is known as a __________

A

one-step growth experiment.

58
Q

Not all infections of bacterial cells proceed as described above to produce more viral particles and terminate in lysis. An entirely different relationship, known as _______, may develop between the virus and its bacterial host. A bacteriophage can be capable of replicating in step with its host bacterium, being thus transmitted through cell divisions without necessarily causing lysis.

A

lysogeny

59
Q

In lysogeny the viral DNA of the temperate phage, instead of usurping the functions of the cell’s genes, is incorporated into the host’s DNA and becomes a gene in the bacterial chromosome as a _______. In this situation the bacterium metabolizes and reproduces normally, the viral DNA being transmitted to each daughter cell through all successive generations. That a bacterium is infected with a lysogenic (temperate) phage can be detected by the fact that it is “immune” to the same or related phages and that it has potential of making phage when induced.

A

prophage

60
Q

Sometimes, for reasons unknown, the viral DNA is removed from the host’s chromosome and enters the lytic cycle. A change from lysogeny to lysis can sometimes be induced by ________

A

irradiation with UV light or by exposure to some chemicals.

61
Q

There are three important results of lysogeny: In the first one, the lysogenic cells become _______ to reinfection by the same phage (however, the host cell is not immune to infection by other phage types).

A

immune

62
Q

There are three important results of lysogeny: The second result of lysogeny is _______ _______, that is, the host cell may exhibit new properties.

A

phage conversion

63
Q

The third result of lysogeny is that it makes ________ ________possible.

A

specialized transduction

64
Q

The transfer of genetic material from one bacterium to another through the agency of a virus is

A

Transduction

65
Q

Bacterial genes can be transferred to another bacterium in a process called _________ _______. In other word, it is the virus-mediated gene transfer of host DNA from one donor cell to another recipient one.

A

generalized transduction

66
Q

Any bacterial genes can be transferred by __________ __________because the host chromosome is broken down into fragments, any of which can be packaged into a phage coat.

A

generalized transduction

67
Q

In ________ __________, however, only certain bacterial genes can be transferred. _________ _______ is mediated by a lysogenic phage, which packages bacterial DNA along with its own DNA in the same capsid. When a prophage is excised from the host chromosome, adjacent genes from either side may remain attached to the phage DNA.

A

specialized transduction, Specialized transduction

68
Q

Bacteriophages are present in:

A

Freshwater environments 
Marine environments 
Soil 
In water and wastewater treatment plants

69
Q

Bacteriophages can be used as indicators of fecal pollution as indicators of

A

Feces 
Domestic sewage 
Pathogens (ie coliforms) 
Waste and wastewater treatment efficiency  Environmental fate of enteric viruses 
Water movement in surface waters and groundwater

70
Q

They are antibiotic like substances that are highly specific both in the organisms that produce them and the organisms to which they are lethal. They are produced by certain strains of bacteria and act only against closely related organisms. Because of the specificity of their action they can be used for typing bacteria against which they act.

A

Bacteriocins

71
Q

Chemically, bacteriocins are _________. However, like bacteriophages they act by adsorption on specific receptors on the host cell wall.

A

polypeptides

72
Q

Like a prophage, the synthesis of bacteriocin can be induced by UV light, mitomycin C, and other agents. Bacteriophage can be differentiated from bacteriocins by the fact that bacteriocin is degraded by ________ but phage is _______ - _________

A

trypsin, typsin-resistant.

73
Q

These are viral agents that attack a wide range of blue-green algae. They are very similar to bacteriophages both in structure and in infection cycle

A

Cynophages

74
Q

the so-called blue green algae are not true algae rather they belong to a group of bacteria known as ____________. The blue-green algae are prokaryotic in cellular structure although their photoautotrophic metabolism resembles that of green eukaryotic plants.

A

cyanobacteria

75
Q

Viruses attacking fungi are _________. They have been reported in species representing each of the major taxonomic classes of fungi.

A

Mycophages

76
Q

Although viral particles have been observed in many species of fungi, only a few fungal viruses have been described in detail. They are all small polyhedral or spherical particles. They all contain double stranded _______.

A

RNA

77
Q

Fungal cultures infected with virus grow to maturity (that is why they were discovered much later). They are released upon aging of the cultures probably as a consequence of cell autolysis.

A

cell autolysis

78
Q

The multiplication of animal viruses follows the basic pattern of bacteriophage multiplication but has several differences. Animal viruses differ from phages in their mechanism of _____________. Also, once the virus is inside, the _________ and _________ of the new viral components are somewhat different, partly because of the differences between prokaryotic cells and eukaryotic cells. Animal viruses may have certain types of _________ not found in phages. Finally, the mechanisms of maturation and release, and the effects on the host cell, differ in animal viruses and phages.

A

entering the host cell, synthesis and assembly, enzymes

79
Q

The cancer-causing alterations to cellular DNA affect parts of the genome called ________. Viruses capable of inducing tumors in animals are called _________ _______

A

Oncogenes, Oncogenic viruses.

80
Q

Examples of DNA oncogenic viruses

A

Hepatitis B virus HBV

81
Q

Example of RNA oncogenic viruses

A

T-cell leukemia viruses

82
Q

The viral cause of cancer can often go unrecognized for several reasons. First, most of the particles of some viruses infect cells but do not induce cancer. Second, cancer might not develop until long after viral infection. Third, cancers do not seem to be contagious, as viral diseases usually are.

A

3 reasons why the viral cause of cancer can often go unrecognized

83
Q

Example of latent infection

A

Chickenpox virus to shingles

84
Q

Other infectious diseases that have not been found to have a viral cause might be caused by ________. In 1982, American neurobiologist Stanley Prusiner proposed that infectious proteins caused a neurological disease in sheep called _________. The infectivity of scrapie-infected brain tissue is reduced by treatment with proteases but not by treatment with radiation, suggesting that the infectious agent is pure protein. He coined the name prion for proteinaceous infectious particle. Nine animal diseases including the “mad cow disease” fall into this category.

A

prions, scrapie

85
Q

In laboratories, plant viruses are cultured in __________ (plant cells with the cell walls removed) and in insect cell cultures. Some plant diseases are caused by _______, short pieces of naked RNA with no protein coat. Infections with viroids, such as potato spindle tuber viroid, result in losses of millions of dollars from crop damage.

A

protoplasts, viroids

Microbiology LFS 261 (17 decks)

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