Lecture 4 Viruses and other Acellular infectious agents Flashcards Preview

Microbiology > Lecture 4 Viruses and other Acellular infectious agents > Flashcards

Flashcards in Lecture 4 Viruses and other Acellular infectious agents Deck (168):
1

Acellular Agents

viruses, Viroids, Satellites, Prions

2

Type of acellular agent that is protein and nucleic acid

Viruses

3

Type of Acellular agent that is only RNA

Viroids

4

Type of Acellular agent that is only nucleic acids

Satellites

5

Type of acellular agent that is only proteins

Prions

6

Viruses are a major cause of _____

disease

7

Viruses are important members of ____ world

aquatic

8

Are viruses important in evolution

yes

9

Viruses are important ____ systems in molecular biology

model

10

Bacterial viruses are called ______

bacteriophages (phages)

11

There are ___ archaeal viruses

few

12

Most viruses are ____ viruses

eukaryotic (plants, animals, protists, and fungi)

13

Viruses are classified into families based on

genome, structure, life cycle, morphology, genetic relatedness

14

a complete virus particle is called a ____

virion

15

General Properties of Viruses

- a complete virus particle
- consists of greater than or equal to 1 molecule of DNA or RNA enclosed in coat of protein
- May have additional layers
- cannot reproduce independent of living cells nor carry out cell division (but can exist extracellularly)

16

A virion size range is about ______ nm in diameter and most viruses must be viewed with an _____-

10-400 nanometers, electron microscope

17

All virions contain a _____ which is composed of ______ and a ______

nucleocapsid, which is composed of nucleic acid (DNA or RNA) and a protein coat (capsid)

18

What are the protein subunits of a virion capsid called

capsomeres

19

All Virion structure

- Nucleic Acid (DNA or RNA) (Single or double stranded)
- Capsid (Protein coat) (Protein subunits= Capsomeres)

20

All virions contain a nucleocapsid which is composed of ____ and a _____ but some consist only of a nucleocapsid, others have additional components called ____

Nucleic acid (DNA or RNA) and protein coat (capsid), Envelopes

21

The enveloped that surrounds the nucleocapsid of viruses usually has viral proteins called ____ inserted into it

spikes

22

What are the three types of capsid symmetry

- helical
- icosahedral
- complex

23

The envelope that surrounds some viruses is composed of

combination of lipids and carbohydrates , and proteins

24

Envelope lipids and carbohydrates are acquired from the ____. while envelope proteins are coded for by _____ and may even project form the envelope surface as ____

host, viral genes, spikes (also called peplomers)

25

What is the function of envelope spikes (peplomers)

attachement to host cell surface

26

General Characteristics of Viruses

- Obligatory intracellular parasites
- Contain DNA or RNA
- Contain a protein coat (note that the DNA/RNA and protein coat make up the nucleocapsid present in all viruses)
- Some are enclosed by an envelope
- Some viruses have spikes
- Most viruses infect only specific types of cells in one host
- Host range is determined by specific host attachment sites and cellular factors

27

Large macromolecular structures which serve as protein coat of virus

Capsids

28

Functions of virus capsid

Protect viral genetic material and aids in its transfer between host cells

29

Virus Capsids are made of protein subunits called

protomers or capsomeres

30

Viruses are classified by ___-

morphology

31

examples of viruses classified by morphology

- helical viruses
- polyhedral viruses
- Enveloped Viruses
- Complex viruses

32

Viruses shaped like hollow tubes with protein walls

Helical Capsids

33

In helical capsids ____ self assemble

protomers

34

In helical capsids the size of the capsid is a function of ______

nucleic acid

35

Examples of helical viruses

- Rabies
- Ebola hemorrhagic feber

36

a _____ is a regular polyhedron with 20 equilateral faces and 12 vertices

icosahedron

37

An icosahedron is a regular polyhedron with ____ equilateral faces and ___ vertices

20, 12

38

______ are the most efficient way to enclose a space

Icosahedral capsids

39

Icosahedral capsids are composed of ____, which are ring or knob-shaped units, each usually 5 or 6 protomers

Capsomers

40

5 subunit capsomers are called

Pentamers (pentons)

41

6 subunit capsomers are called

Hexamers (hexons)

42

Pentamers are usually at the ____ of the icosahedron, whereas hexameters generally form its ____ and ____

vertices, edges and triangular faces

43

Example of polyhedral virus

- Adenovirus
- Poliovirus

44

what is the largest animal virus

poxvirus

45

Viruses that do not fit into the category of helical or icohedral capsids are called

Capsids of complex symmetry

46

Examples of complex viruses

- Poxvirus
- Large bacteriophages

47

some Large bacteriophages have ____ symmetry

binal (head resembles icosahedral, tail is helical)

48

many viruses are bound by an outer, flexible, membranous layer called the ____

envelope

49

Animal virus envelopes (lipids and carbohydrates) usually arise from

host cell plasma or nuclear membranes

50

Examples of enveloped viruses

- Influenza virus
- Herpes simplex virus
- rabies

51

Envelope proteins, which are viral encoded, may project from the envelope surface as ____/____

spikes/peplomers

52

functions of envelope protein, spikes/peplomers?

- involved in viral attachment to host cell
- used for identification of virus
- may have enzymatic or other activity
- may play role in nucleic acid replication

53

The influenza virus has spikes that consist of enzyme ________, which functions in the release of mature virions from the host cell

Neuraminidase

54

The influenza virus has spikes that consist of _____ proteins, so named because they bind virions to red blood cells and cause the cells to clump together- a process called ______

hemagglutinin, hemagglutination

55

Do virions have a variety of enzymes

yes

56

Some other virus enzymes are associated with the ____ or ____ but most are within the _____

envelope or capsid, but most are within the capsid

57

Characteristics of the viral genome

- Diverse nature of genomes
- a virus may have single or double stranded DNA or RNA
- The length of the nucleic acid also varies form virus to virus
- Genomes can be segmented or circular

58

What is the first step in the life cycle of a virus

attachment (often called absorption)

59

Steps of animal viruses life cycle

- Attachement: viruses attach to cell membrane
- Penetration/Entry: Endocytosis or fusion
- Uncoating: viral or host enzymes
- Biosynthesis: Production of nucleic acid
- Maturation: Nucleic acid and capsid proteins assemble
- Release: by buddying (enveloped viruses) or rupture (lysis)

60

HIV binds to what two proteins on human cells

CD4 and CCR5

61

attachement (adsorption) of virus is ____ specific

receptor

62

The receptor determines host preference for attachment (adsorption) of virus: may be ______, _______, _____, ____

may be specific tissue, may be more than one host, may be more than one receptor, maybe in lipid rafts providing entry of virus

63

after attachment to the host cell, the virus's ____ or the entire ____ enter the cytoplasm

genome or entire nucleocapsid

64

Viral entry and uncoating varies between ___ or ____ virus

naked or enveloped

65

What are the 3 methods of viral entry and uncoating

- fusion of the viral envelope with host membrane; nucleocapsid enters
- endocytosis in vesicle; endosome (and endosomal enzymes) aid in viral uncoating
- Injection of nucleic acid

66

RNA virus must carry in or synthesize the _____ proteins necessary to complete synthesis

proteins

67

___ proteins are important in the assembly phase of the virus life cycle

late

68

The ____,___, and ___ of the of a bacteriophage T4 are assembled separately.

baseplate, tail fibers, and head components

69

for many viruses, so-called "virus factories" are generated. These are large ______ of either complete nucleocapsids or procapsids

paracrystalline clusters

70

nonenveloped viruses ___ the host cell for release

lyse

71

during the release of non enveloped viruses viral proteins may attack ____ or ____

peptidoglycan or membrane

72

Lysozyme function in non enveloped viruses

attacks peptidoglycan in the host's cell wall

73

What is the function of holin in non-enveloped viruses

creates holes in plasma membrane, thus enabling virus to move from the cytoplasm to the peptidoglycan

74

Enveloped viruses are released via

budding

75

Explain enveloped viruses being released via budding

- viral proteins are placed into host membrane
- nucleocapsid may bind to viral proteins
- envelope derived from host cell membrane, but may be Golgi, ER, or other
- Virus may use host actin tails to propel through host membrane

76

Special features of Biosynthesis of single stranded DNA

Cellular enzyme transcribes viral DNA in nucleus

77

Special features of Biosynthesis of double stranded DNA

- Cellular enzyme transcribes viral DNA in nucleus
- Viral enzyme transcribes viral DNA in virion, in cytoplasm

78

Special features of Biosynthesis ofDNA, reverse transcriptase

- Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA

79

Special features of Biosynthesis of RNA, + strand

Viral RNA functions as a template for synthesis of RNA synthesis of RNA polymerase which copies- strand RNA to make mRNA in cytoplasm

80

Special features of Biosynthesis of RNA, - strand

Viral enzymes copies viral RNA to make mRNA in cytoplasm

81

Special features of Biosynthesis of RNA, double-stranded

Viral enzyme copies - strand RNA to make mRNA in cytoplasm

82

Special features of Biosynthesis of RNA, Reverse transcriptase

Viral enzyme copies viral RNA to make DNA in cytoplasm; DNA moves to nucleus

83

Parvovirdae is what type of viral nucleic acid

DNA, single-stranded

84

Herpesviridae, papovavidae, and poxviridae are what type of viral nucleic acid

DNA, Double-stranded

85

Hepadnaviridae is what type of viral nucleic acid

DNA, reverse transcriptase

86

Picornaviridae and Togaviridae are what type of viral nucleic acid

RNA, + strand

87

Rhabdoviridae is what type of viral nucleic acid

RNA, - strand

88

Reoviridae is what type of viral nucleic acid

RNA, double stranded

89

Retroviridae is what type of viral nucleic acid

RNA, reverse transcriptase

90

lack of information on ___ and ____ history makes viral classification difficult

origin and evolutionary

91

A uniform classification system for virus taxonomy was developed in 1971 by the

Internal committee for Taxonomy of viruses (ICTV)

92

Most current reports their are _____ viruses, ___ orders, ____ families, ___ subfamilies, and ____ genera

2,000, 6, 87, 19, 349

93

Virus classification according to internal committee for taxonomy of viruses (ICTV) is based on numerous characteristics such as

- nucleic acid type
- presence or absence of envelope
- Capsid symmetry
- Dimensions of virion and capsid

94

The alternative virus classification scheme was created by ____ and focuses on

David Baltimore, focuses on viral genome and process used to synthesize viral mRNA

95

The baltimore classification system is based on ___ life cycles groups based on, which are

7
- double stranded (ds) DNA
- Single stranded (ss) DNA
- dsRNA
- ssRNA (+ or - strand)
- retrovirus

96

Viral DNA can be integrated into a host cell chromosome as a provirus by _____

viral integrase

97

What is a provirus

A stage in a retrovirus life cycle when viral DNA is integrated into a host cell chromosome by viral integrase

98

Bacteriophages can with be _____ or _____

virulent or temperate

99

Virulent phages only have one reproductive option which is

begin multiplying immediately upon entering its bacterial host, followed by release form the host by lysis

100

T4 is an example of a _____ phage

virulent

101

Temperate phages have two reproductive options which are

- they can multiply like a virulent phage and lyse the host cell
- or they can remain within the host without destroying it

102

The relationship between a temperate phage and its host is called

lysogeny

103

Lysogenic bacteria reproduce and in most other ways appear to be normal. however, they have two distinct characteristic, which are

- they cannot be reinffected by the same virus, that is they have immunity to superinfection
- as they reproduce, the prophage is replicated and inherited by progeny cells

104

Many temperate phages integrate their genome into host genome (becoming _____ in a ______) in a relationship called lysogeny

Prophage, lysogenic bacterium

105

what are the two advantages to lysogeny for virus

- phage remains viable but may not replicate
- multiplicity of infection ensures survival of host cell

106

under appropriate conditions infected bacteria will lyse and release temperate phage particles. This occurs when conditions in the cell cause the prophage to initiate synthesis of new phage particles , a process called ____

conditions in the cell cause the prophage to initiate synthesis of new phage particles , a process called induction

107

Temperate phage changes ______ of its host. Phage may express ____ or ___

phenotype, pathogenic toxin or enzyme

108

most archaeal viruses are ____

temperate

109

Archaeal viruses can be ___ or __-

lytic or temperate

110

______ infection results in cell death through lysis

cytocidal

111

____ infections may last years

persistent

112

Cytopathic effects (CPEs)

- degenerative changes
- abnormalities

113

a slow release of virus without cell death is caused by ___ infection

chronic viral infection

114

activation of host proto-oncogene (human) or insertion of oncogene (other animals) can lead to

transformation into malignant cell

115

Virus remains in asymptomatic host cell for long period is called ____ infection

latent infection

116

Examples of latent infection

Cold sores, shingles

117

in ____ viral infections disease process occurs over a long period; generally is fatal

Chronic viral infection

118

examples of chronic viral infection

subacute sclerosing panencephalitis (measles virus)

119

abnormal new cell growth and reproduction due to loss of regulation

neoplasia

120

reversion of cell to a more primitive or less differentiated state

anaplasia

121

___ tumors remain in place

benign

122

Growth or lump of tissue

tumor

123

Spread of cancerous cells throughout body

Metastasis

124

carcinogenesis is a complex, ____ process, that often involves ____

multistep process, often involves oncogenes

125

oncogenes may come from the virus or may be transformed

host proto-oncogenes (involved in normal regulation of cell growth/differentiation)

126

Human herpesvirus 8 (HHV8) causes what kind of cancer

Several, including Kapok's sarcoma

127

Epstein-Barr virus (EBV) causes what kind of cancer

Several, including Burkitt's lymphoma and nasopharyngeal carcinoma

128

Hepatitis B virus causes what kind of cancer

Hepatocellular carcinoma

129

Hepatitis C virus causes what kind of cancer

Liver cancer

130

Human papillomaviruses (HPV) strains 6, 11, 16, and 18 cause what kind of cancer

Cervical cancer

131

Human T-cell lymphotropic virus 1 (HTLV-1) causes what kind of cancer

T-Cell leukemia

132

Possible mechanisms by which viruses cause cancer

- Viral proteins bind host cell tumor suppressor proteins
- Carry oncogene into cell and insert it into host genome
- Altered cell regulation
- Insertion of promotor or enhancer next to cellular oncogene

133

The cultivation of viruses requires _____ of appropriate living host

inovulation

134

Bacterial and Archaeal viruses are usually cultivated in ___ or ____ cultures of suitable, young, actively growing bacteria

- broth
- agar

135

Broth cultures lose ____ as viruses reproduce

turbidity

136

____ are observed on agar cultures

Plaques

137

Animal viruses are cultivated using ____ cultures

Tissue (Cell)

138

Localized area of cellular destruction and lysis that enlarges as the virus replicates (on tissue (cell) culture)

Viral plaques

139

Microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues

Cytopathic effects (CPEs)

140

Hosts for plant viruses

- Plant tissue cultures
- Plant protoplast cultures
- Suitable whole plants

141

Plant viruses in suitable whole plants may cause ____ lesions or ______

localized necrotic lesions or generalized symptoms of infection

142

How to quantify virus on culture

- direct counting- count viral particles
- Indirect counting by an observation of virus- hemagglutination assay and plaque assays

143

PFU/ml=

number of plaques/sample dilution

144

explain plaque assays

- indirect assay that determines virion numbers based on their infectivity.
- dilutions of virus preparation are made and planted on lawn of host cells. Then the plaques are counted. results expressed as plaque-forming units (PFU)
- PFU/ml = number of plaques/sample dilution

145

what does a high multiplicity of infection mean (MOI)

more phages in an environment than there are host cells

146

In plaque assays when the multiplicity of infection (MOI) is very low, each plaque in a layer of host cells is assumed

to have arisen from the multiplication of a single virion

147

The ____ dose is the dilution that contains a concentration (dose) of virions large enough to destroy 50% of the host cells or organisms

lethal dose (LD50)

148

The _____ dose is the dose that causes 50% of the host organisms to become infected

infectious dose (ID50)

149

____ are covalently closed, circular ssRNAs, about 250 to 370 nucleotides long

Viroids

150

Viroids replicate by a host cell enzyme called ________

DNA-dependent RNA polymerase

151

Viroids cause ____ disease

plant

152

Do viroids encode gene products

No!!!

153

some data suggest that viroids cause disease by triggering a eukaryotic response called _____, which normally functions to protect against infection by darn viruses

RNA silencing

154

Infectious nucleic acids (DNA or RNA)

infectious nucleic acids

155

Satellite viruses encode their own _____ proteins when helped by a ____ virus

capsid, helper

156

Satellite RNAs/DNAs do not encode their own ______

capsid proteins

157

satellites differ from viroids in that they

- may encode one or more gene products
- need a helper virus to replicate and infect host cells

158

satellites are divided into what three types

Satellite viruses, Satellite RNAs, and satellite DNAs

159

Satellite viruses encode their own ______, whereas satellite RNAs and DNAs do not

capsid proteins

160

Human Hepatitis D virus is a _____ and requires ______ as a helper virus for replication

human hepatitis D virus is a satellite and requires Human hepatitis B virus as a helper virus for replication

161

Proteinaceous infectious particle

Prions

162

Examples of prions

- Scrapie in sheep
- Bovine spongiform encephalopathy (BSE) or mad cow disease
- Creutzfeldt-Jakob disease (CJD) and variant CJD (vCJD) in humans
- Kuru in humans

163

priions cause a variety of

degenerative diseases in humans and animals

164

PrP^c stands for

prion protein in normal form

165

PrP^Sc stands for

(scrapie-associated) prion protein in the abnormal form

166

All prion caused diseases have ____ effective treatment, and result in

No effective treatment, and result in progressive degeneration of the brain and eventual death

167

Interaction of PrP^Sc with PrP^c may cause PrP^c to ____ and ____

crosslink and trigger apoptosis

168

What distinguishes a chronic viral infection from a latent viral infection?

The infectious virus gradually builds up over a long period of time