Lecture 12

Question 1

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

Answer 1

Viruses

Question 2

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

Answer 2

host.

Question 3

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

Answer 3

infection

Question 4

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

Answer 4

virions.

Question 5

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

Answer 5

Genome

Question 6

A fully formed virus particle is referred to as what?

Answer 6

viron

Question 7

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

Answer 7

Animal viruses Plant viruses Bacterial viruses (bacteriophages)

Question 8

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

Answer 8

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

Question 9

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

Answer 9

bacterial viruses

Question 10

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

Answer 10

capsid

Question 11

Each capsid is composed of protein subunits called _________.

Answer 11

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

Question 12

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

Answer 12

lipids, proteins, and carbohydrates.

Question 13

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

Answer 13

spikes

Question 14

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

Answer 14

antibodies

Question 15

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

Answer 15

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

Question 16

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.

Answer 16

Helical viruses, polyhedral viruses, enveloped viruses, complex viruses

Question 17

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

Answer 17

Helical viruses

Question 18

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.

Answer 18

icosahedron, 20, 12

Question 19

Enveloped viruses are roughly what shape?

Answer 19

spherical

Question 20

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

Answer 20

enveloped helical or enveloped polyhedral viruses.

Question 21

Example of enveloped helical virus

Answer 21

influenzavirus

Question 22

Example of enveloped polyhedral viruses

Answer 22

herpes simplex virus

Question 23

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

Answer 23

ICTV - International Committee on the Taxonomy of Viruses

Question 24

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

Answer 24

1] Nucleic acid type 2] Strategy for replication

3] Morphology

Question 25

The suffix -virus is used for the _______ names

Answer 25

genus

Question 26

Virus Family names end in -_______

Answer 26

viridae

Question 27

Virus Order names end in -________

Answer 27

ales

Question 28

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

Answer 28

virus species

Question 29

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

Answer 29

FYI

Question 30

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

Answer 30

living cells or host cell

Question 31

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

Answer 31

1. Living animals 2. Embryonated eggs 3. Cell cultures

Question 32

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

Answer 32

lentiviruses.

Question 33

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.

Answer 33

T cells, gamma globulin.

Question 34

Viral growth is signaled by what 3 things?

Answer 34

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

Question 35

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

Answer 35

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.)

Question 36

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

Answer 36

culture media

Question 37

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

Answer 37

primary or continuous

Question 38

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

Answer 38

Primary cell lines

Question 39

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

Answer 39

continuous cell lines

Question 40

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

Answer 40

antibiotics

Question 41

Viruses that use bacterial cells as a host

Answer 41

bacteriophages

Question 42

much of our understanding of viral multiplication has come from _________

Answer 42

bacteriophages.

Question 43

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.

Answer 43

plaque method

Question 44

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

Answer 44

plaque-forming units.

Question 45

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

Answer 45

Lytic cycle and Lysogenic cycle

Question 46

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

Answer 46

Lytic cycle

Question 47

In what phage multiplication mechanism does the host remain alive?

Answer 47

lysogenic cycle

Question 48

The first step in reproduction of a bacteriophage is __________

Answer 48

adsorption (attachment)

Question 49

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

Answer 49

The tip of the phage tail

Question 50

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.

Answer 50

cations, “phage lysozyme”

Question 51

Penetration is achieved when what three things occur?

Answer 51

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

Question 52

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.

Answer 52

DNA or RNA

Question 53

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 _____ _____

Answer 53

nucleic acids, nucleic acids.

Question 54

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.

Answer 54

25, 200

Question 55

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

Answer 55

burst time

Question 56

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

Answer 56

burst size

Question 57

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

Answer 57

one-step growth experiment.

Question 58

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.

Answer 58

lysogeny

Question 59

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.

Answer 59

prophage

Question 60

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 ________

Answer 60

irradiation with UV light or by exposure to some chemicals.

Question 61

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).

Answer 61

immune

Question 62

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

Answer 62

phage conversion

Question 63

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

Answer 63

specialized transduction

Question 64

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

Answer 64

Transduction

Question 65

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.

Answer 65

generalized transduction

Question 66

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.

Answer 66

generalized transduction

Question 67

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.

Answer 67

specialized transduction, Specialized transduction

Question 68

Bacteriophages are present in:

Answer 68

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

Question 69

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

Answer 69

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

Question 70

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.

Answer 70

Bacteriocins

Question 71

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

Answer 71

polypeptides

Question 72

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 _______ - _________

Answer 72

trypsin, typsin-resistant.

Question 73

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

Answer 73

Cynophages

Question 74

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.

Answer 74

cyanobacteria

Question 75

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

Answer 75

Mycophages

Question 76

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 _______.

Answer 76

RNA

Question 77

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.

Answer 77

cell autolysis

Question 78

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.

Answer 78

entering the host cell, synthesis and assembly, enzymes

Question 79

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

Answer 79

Oncogenes, Oncogenic viruses.

Question 80

Examples of DNA oncogenic viruses

Answer 80

Hepatitis B virus HBV

Question 81

Example of RNA oncogenic viruses

Answer 81

T-cell leukemia viruses

Question 82

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.

Answer 82

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

Question 83

Example of latent infection

Answer 83

Chickenpox virus to shingles

Question 84

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.

Answer 84

prions, scrapie

Question 85

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.

Answer 85

protoplasts, viroids