Microbiology - Chapter 6 An Introduction To The Viruses

Front 1

Who first proposed the term "virus"?

Back 1

Louis Pasteur

Front 2

Who showed that that a disease in tobacco was caused by a virus in the 1890s

Back 2

Ivanovski and Beijerinck

Front 3

Who discovered an animal virus that causes foot –and-mouth disease in cattle

Back 3

Loeffler and Frosch

Front 4

Viruses can infect _____ _____ __ ____

Back 4

every type of cell

Front 5

Why aren't viruses considered to be living things?

Back 5

Cannot exist independently from the host cell

Front 6

why are viruses considered more than lifeless molecules?

Back 6

Because they can direct life processes

Front 7

what are viruses called?

Back 7

infectious particles, either active or inactive

Also called obligate intracellular parasites

Front 8

what is the general way a virus multiplies

Back 8

they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses

Front 9

what is needed to see most viruses?

Back 9

electron microscope

Front 10

what is the smallest infectious agent known?

Back 10

viruses

Front 11

How are viruses viewed?

Back 11

Special stains and an electron microscope
Negative staining outlines the shape
Positive staining shows internal details
Shadowcasting technique

Front 12

what is the general molecular structure of viruses?

Back 12

composed of regular, repeating subunits that give rise to their crystalline appearance

Front 13

what are the two parts of a virus?

Back 13

external coating
core

Front 14

what does the external coating consist of?

Back 14

capsid
envelope in 13 of the 20 families of animal viruses OR

Front 15

what does the core consist of

Back 15

DNA (Single or Double)
RNA (Single or Double)

Front 16

If there is no envelope, it is called a ______ ________

Back 16

naked virus

Front 17

what is the capsid and the nucleic acid together called?

Back 17

nucleocapsid

Front 18

define "virion"

Back 18

Fully formed virus that is able to establish an infection in a host cell- virion

Front 19

The viral capsid is the ______ _____ ______
It is constructed from _______ _______ called ________
Made up of _______ ______

Back 19

Protective Outer shell
identical subunits, capsomers
protein molecules

Front 20

what are the two different types of capsomers?

Back 20

1. Helical
2. Icosahederal

Front 21

describe helical capsids

Back 21

Rod-shaped capsomers
Assemble in to helical nucleocapsid

Front 22

describe icosahederal capsids

Back 22

Three-dimensional, 20-sided figure with 12 evenly spaced corners
Although they all display this symmetry, there are wide variations

Front 23

what is an enveloped virus?

Back 23

Enveloped viruses take a bit of the host cell membrane in the form of an envelope

Front 24

what happens in the host cell membrane that the enveloped virus has taken?

Back 24

In the envelope, some or all of the regular membrane proteins are replaced with viral proteins

Front 25

what happens with the viral proteins in the membrane?

Back 25

Some proteins form a binding layer between the envelope and the capsid
Glycoproteins remain exposed as spikes (peplomers)- essential for attachment

Front 26

what are the functions of the viral capsid/envelope

Back 26

Protects nucleic acids
Help introduce the viral DNA or RNA into a suitable host cell
Stimulate the immune system to produce antibodies that can protect the host cells against future infections

Front 27

define "genome"

Back 27

Genome- the sum total of the genetic information carried by an organism

Front 28

how do the number of viral genes compare with cells genes

Back 28

Number of viral genes compared with a cell- quite small
They only have the genes necessary to invade host cells and redirect their activity

Front 29

What are some exceptions to the commonly small amount of genes?

Back 29

Parvoviruses contain single-stranded DNA
Reoviruses contain double-stranded RNA

Front 30

Describe DNA viruses

Back 30

ssDNA
dsDNA
linear
circular

Front 31

describe RNA viruses

Back 31

Mostly single-stranded
Segmented- individual genes exist on separate pieces of RNA

Front 32

single stranded RNA is divided into two groups: describe each

Back 32

Positive-sense RNA: genomes that are ready for immediate translation into proteins
Negative-sense RNA: genomes have to be converted into the proper form to be made into proteins

Front 33

DNA viruses can be either _____ or ________

Back 33

enveloped or nonenveloped

Front 34

Enveloped DNA viruses can be

Back 34

only double stranded

Front 35

nonenveloped DNA can be

Back 35

either double or single stranded

Front 36

describe a retrovirus

Back 36

an RNA enveloped genome that is single-stranded and encodes reverse transcriptase, which reverse transcripts RNA to DNA

Front 37

what are some Other Substances in the Virus Particle

Back 37

Can contain enzymes for specific operations within the host cell
Polymerases to synthesize DNA and RNA
Replicases to copy RNA (RNA dependent RNA polymerase)
Integrase (Allows for integration of viral genome into host genome)

Front 38

what are the main criteria for how viruses are classified and named?

Back 38

Structure
Chemical composition
Similarities in genetic makeup

Front 39

the International Committe on the Taxonomy of Viruses in 2000 designated how many:
orders?
Families?
Genera?

Back 39

3
63 - "-viridae"
263 - "virus"

Front 40

What are the multiplication cycles in animal viruses?

Back 40

Adsorption
Penetration
Uncoating
Synthesis
Assembly
Release

Front 41

describe the adsorption stage

Back 41

Virus encounters susceptible host cells
Adsorbs specifically to receptor sites on the cell membrane
Because of the exact fit required, viruses have a limited host range

Front 42

Describe the penetration stage
(different ways of penetration)

Back 42

Flexible cell membrane of the host is penetrated by the whole virus or its nucleic acid
Endocytosis: entire virus engulfed by the cell and enclosed in a vacuole or vesicle
The viral envelope can also directly fuse with the host cell membrane

Front 43

Describe the uncoating stage

Back 43

Enzymes in the vacuole dissolve the envelope and capsid
The virus is now uncoated

Front 44

Describe the general synthesis stage

Back 44

Free viral nucleic acid exerts control over the host’s synthetic and metabolic machinery

Front 45

Describe the synthesis stage with DNA viruses

Back 45

DNA viruses- enter host cell’s nucleus where they are replicated and assembled
DNA enters the nucleus and is transcribed into RNA
The RNA becomes a message for synthesizing viral proteins (translation)
New DNA is synthesized using host nucleotides

Front 46

*

Back 46

*

Front 47

Describe the synthesis stage with RNA viruses

Back 47

RNA viruses- replicated and assembled in the cytoplasm

Front 48

Describe the Assembly stage

Back 48

Mature virus particles are constructed from the growing pool of parts

Front 49

Describe the Release stage

Back 49

Nonenveloped and complex viruses are released when the cell lyses or ruptures
Enveloped viruses are liberated by budding or exocytosis
Anywhere from 3,000 to 100,000 virions may be released, depending on the virus

Front 50

Entire length of cycle- anywhere from

Back 50

8 to 36 hours

Front 51

define cytopathic effects

Back 51

virus-induced damage to the cell that alters its microscopic appearance

Front 52

what are inclusion bodies?

Back 52

Inclusion bodies- compacted masses of viruses or damaged cell organelles

Front 53

THe specific cytopathic effects of a virus is important for the _______ of _______ _______.

Back 53

diagnosis of viral infections

Front 54

what is an oncogenic virus?

Back 54

viruses that enter their host cell and permanently alter its genetic material, leading to cancer

Front 55

what are oncoviruses?

Back 55

Oncoviruses- mammalian viruses capable of initiating tumors

Front 56

what is a virus that infects bacteria called?

What do most of them contain?
What effect do they have on the bacteria they infect?

Back 56

bacteriophage
most contain dsDNA
Often make the bacteria they infect more pathogenic for humans

Front 57

Describe the physical appearance of T-even Phages

Back 57

Icosahedral capsid head containing DNA
Central tube surrounded by a sheath
Collar
Base plate
Tail pins
Fibers

Front 58

+

Back 58

+

Front 59

Describe the stages of T-even Phages

Back 59

Adsorb to host bacteria
The nucleic acid penetrates the host after being injected through a rigid tube inserted through the bacterial membrane and wall
Entry of the nucleic acid causes the cessation of host cell DNA replication and protein synthesis
The host cell machinery is then used for viral replication and synthesis of viral proteins
As the host cell produces new parts, they spontaneously assemble

Front 60

T-even Phages cycle

Back 60

Front 61

*

Back 61

*

Front 62

what are temperate phages?

Back 62

Temperate phages- special DNA phages that undergo adsorption and penetration but are not replicated or released immediately
Instead the viral DNA enters an inactive prophage stage
Lysogeny: the cell’s progeny will also have the temperate phage DNA

Front 63

*

Back 63

*

Front 64

Define lysogenic conversion

Back 64

Lysogenic conversion: when a bacterium acquires a new trait from its temperate phage

Front 65

what is the difference between bacteriophages and animal viruses during the adsorption stage?

Back 65

bacteriophages have precise attacment of special tail fibers to the cell wall
animal viruses attach via their capsid or envelope to cell surface receptors

Front 66

what is the difference between bacteriophages and animal viruses during the penetration stage?

Back 66

bacteriophages inject their nucleic acid through the cel wall - no uncoating of nucleic acid
animal viruses are fully engulfed and uncoated, or the virus surface fuses with the cell membrane to release nucleic acid.

Front 67

+

Back 67

+

Front 68

what is the difference between bacteriophages and animal viruses during the Assembly stage?

Back 68

both are the same except that bacteriophages assembly occurs only in the cytoplasm, while in animal viruses, assembly occurs in both cytoplasm and nucleus

Front 69

what is the difference between bacteriophages and animal viruses during the release stage?

Back 69

bacteriophages cause the cell to lyse when viral enzymes weaken it,
animal viruses cause some cells to lyse, enveloped viruses bud off host cell membrane

Front 70

Bacteriophages cause cell destruction _________
Animal viruses cause cell destruction ___________

Back 70

immediately upon release
immediately upon release or later (delayed)

Front 71

what are the primary purposes of viral cultivation?

Back 71

To isolate and identify viruses in clinical specimens
To prepare viruses for vaccines
To do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells

Front 72

what is it called when animals are exposed to a virus by injection in order to cultivate the virus?

Back 72

live animal inoculation

Front 73

what is a nearly perfect condition for viral propagation

Back 73

using bird embryos within their eggs.

Front 74

Cell/Tissue culture techniques involve:

How do the cultured cells grow?

Back 74

Animal cell cultures grown in sterile chambers with special media.

In the form of a monolayer

Front 75

viruses are the most common cause of :

Back 75

acute infections that do not result in hospitalization
Most do not cause death but those that do can have very high mortality rates
Others can lead to long-term debility

Front 76

the Deposition of protein fibrils (prions) in the brain tissue is caused by:

Back 76

Spongiform encephalopathies

Front 77

Spongiform encephalopathies cause _______ ________ diseases with ______ _____ __ _______

Back 77

chronic, persistant

long periods of latency

Front 78

what are satellite viruses?

Back 78

Defective forms of viruses
Dependent on other viruses for replication

Front 79

what are viroids?

Back 79

Parasitize plants
Very small
Composed only of naked strands of RNA

Front 80

How do antiviral drugs work?

Back 80

By blocking virus replication by targeting one of the steps in the viral life cycle

Front 81

what drug has shown potential for treating and preventing viral infections?

Back 81

interferon

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