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Flashcards in Test 1 Deck (175):
1

What is virology?

the study of viruses

2

When did the sizes and shapes of the viruses become known?

late 1930s

3

Why weren't the sizes and shapes of the viruses discovered before the 1930's? What inhibited this?

couldn't see it under a light microscope so they had to wait for the electron microscope

4

What are 4 general characteristics of viruses?

1. They are SMALL
2. Need a LIVING cell
3. Have either DNA or RNA genome...but not both
4. Have a RECEPTOR BINDING PROTEIN

5

What is the range in size for how small a virus is in diameter?

20-150nm

6

Why do viruses need a living cell

the virus itself is considered to not be living so it needs a prokaryotic or eukaryotic organism to replicate and survive

7

Why do viruses need a receptor binding protein

thats how they bind and infect a cell, the binding protein allows them to get on the surface of a virus

8

What are the 3 main components of a virus

1. nucleic acid
2. protein coat
3. may or may not have a lipid envelope

9

What is the one goal of a virus

to deliver its genome to host cell which then causes hosts genes to make virus parts

10

How many genes do viruses have

at most 10 genes

11

What type of nucleic acid do viruses have

DNA or RNA

12

Viral genomes range in size from how many basepairs

3000 to 200,000

13

DNA viruses have what type of genome

double stranded

14

How are DNA viruses made into proteins (basic steps)

transcribed into mRNA
translated into protein

15

What type of genome do RNA viruses have

single stranded

16

Which is more stable? DNA or RNA?

DNA is more stable due to having double strand

17

Why does RNA change more rapidly than DNA genomes?

less stable
in DNA there is excess backtracking and proofreading and repair mechanisms that don't exist in RNA

18

Why does RNA have the backtracking and repair mechanisms

because RNA is an intermediate typically while DNA goes through meiosis and mitosis after being copied

19

RNA genomes can be one of what two things?

positive or negative stranded

20

What is different about the steps in positive vs negative stranded RNA

positive- directly translated to protein, it is already mRNA
negative-contain complimentary sequence to positive strand (ex. retrovirus)

21

How is a retrovirus translated

converted back to DNA and then back into the correct strand of RNA then translated into a protein

22

What type of polymerase do humans have?

DNA dependent RNA polymerase

23

What type of polymerase does RNA genome need

RNA dependent RNA polymerase

24

Since humans do not have the RNA dependent RNA polymerase, how does the virus get this?

It brings it along with its genome when it attacks human cell

25

What is another name for the protein coat

capsid

26

What are subunits of the capsid

capsomeres

27

What are the two general shapes of viruses protein coat

helical
icosohedral

28

What is a helical shaped coat

arranged like a spiral staircase

29

What is a icosohedral shaped coat

triangular shape, looks like a golfball

30

What does the nucleic anid and capsid make

nucleocapsid

31

Why do some viruses have a lipid envelope?

they take some of the cell membrane with them as they replicate (have spike membrane proteins that take some of the host membrane with them)

32

How do viruses have spike proteins

they get them through its coding from the viral genome

33

What specific function do the spike proteins have

receptor binding protein for viruses

34

What is a virion

nucleocapsid and envelope

35

What four features are applied to viral classification (named for its characteristics)

1- genome type
2- polarity of genome (+ or -)
3- symmetry of nucleocapsid
4-presence or absence of envelope

36

Why can't viruses duplicate like a human cell

they don't have any of the machinery and mechanisms to duplicate

37

Why do viruses use a host cell

to get the machinery needed for replication

38

Could viruses exist before cells

no

39

How do viruses know which cell to attach to? Is it random?

no the binding is not random. viruses have specific spike proteins that interact with host cell receptors

40

Do host cells have specific viral receptors

no

41

If the cell does not have specific viral receptors, how do viruses attach

the virus attacks the cell using one of its existing receptors and then it acquires the ability to use that receptor

42

What are the ten steps for duplication of a virus

1- host cell recognition and binding
2-internalization (endocytose)
3-"uncoating"
4-transcription (unless positive)
5-translation of early genes
6-early genes function
7- genome replication
8-translation of late genes
9-assembly
10-release

43

What does the step of uncoating allow

genome to get to the cell

44

What are early genes

typically enzymatic functions that play a part in the duplication process

45

What are the two major things needed to get more virus

more genome= more transcribed
more viral proteins expressed from the genome

46

What are late genes

those typically involved with structure

47

What do viruses have on their surface that aids them in the 1st step of replication

receptor binding proteins

48

What do the receptor binding proteins do to the host cell

bind to normal functional receptors and exploit their location

49

The binding that occurs between the receptor and binding protein are what two things

specific and strong

50

What is meant that the binding is specific

each type of virus only infects certain types of cells

51

What is meant that the binding is strong

its a biochemical event that produces strong interactions

52

What occurs in the 2nd step of replication

internalization, the virus gets into the cell

53

What are the 2 general ways of internalization

fusion and receptor mediated endocytosis

54

What is the fusion method of internalization

viral membrane becomes part of the cell membrane

55

What must the virus have to use the fusion method

envelope and fusion proteins on the viral membrane

56

What is the receptor mediated endocytosis method of internalization

virus binds to a receptor, coated pit forms in cell membrane, inversion of the pit allows it to enter cytoplasm

57

What method of internalization is most common

receptor mediated endocytosis

58

Once the virus is internalized, what two necessary events need to occur

1-production of viral proteins
2-replication of genome

59

What is the process of production of viral proteins

Transcription and translation (since using the cell's machinery the process is the same as cell protein making)

60

What must the virus have in order for viruses to be transcribed and translated

5' cap and 3' tail

61

How do RNA positive strand viruses duplicate?

genome is used directly as mRNA
must have a cap and tail to be recognized
translated to protein

62

How specifically are RNA positive strand viruses duplicated and then what occurs afterwards

they are duplicated by the whole genome at once and then cut into smaller parts

63

How do RNA negative strand viruses duplicate?

RNA genome is complimentary to mRNA
uses a transcriptase and makes complimentary copy of RNA genome that then can be duplicated

64

What is transcriptase and where's it come from

virus associated polymerase in which brought along with the virus before it entered host cell

65

How are RNA retroviruses duplicated (4 steps)

1- RNA genome transcribed by reverse transcriptas to make DNA copy of RNA
2- RNA is digested and replaced by DNA (creates double stranded DNA)
3- Integrase integrates DNA into host cell genome
4- DNA is transcribed to mRNA along with host cell genome and mRNA translated to protein

66

When RNA is replaced by DNA and integrated into host cell DNA, what happens

the proviral DNA has become a permanent part of the host cell genome

67

How is a DNA virus duplicated

viral genome is transcribed to mRNA by host cell and mRNA to a protein

68

Where is a DNA virus duplicated

in the nucleus

69

What is replicase

enzyme that synthesizes a complementary RNA strand of RNA genome and forms a double strand of RNA that serves as a template for synthesis of new RNA viral genomes

70

In positive stranded where does replicase come from

is translated directly from genome in the form of an early gene

71

In negative stranded where does replicase come from

carried by a virus as a protein

72

What specifically is needed for DNA replicaiton

replication form

73

For DNA virus replication, what makes the process rapid

both strands are copied simultaneously

74

What occurs during the step of assembly

capsid forms around nucleic acid

75

Where does assembly typically occur

cytoplasm or at membrane

76

What are the two methods of release of the virus

lytic virus release
enveloped virus release

77

what is lytic virus release

cell bursts and viruses released (there is no envelope to the virus)

78

What is enveloped virus release

bud from the surface, assemble takes place on the membrane, lipid envelope surrounds new virions

79

What is pathogenicity

compares the severity of the disease caused by a different virus

80

what does the prefix patho mean

disease

81

what is virulence

the severity of the disease caused by the same virus

82

How does a small change affect virulence

a small change in the viral genome can cause large changes in the virulence in that it can weaken it or make it stronger

83

What particular aspect of the genome would change the virulence

spike protein receptor proteins that cause the initial degree of infection

84

What types of diseases are caused on a cellular level because of a virus (5 things)

1- cell lysis
2-cells fuse together
3-malignancy
4-inclusion bodies
5-triggers immune response to infected cells

85

What is synctia

giant multinucleated cells

86

What are the steps for viruses causing disease in the entire body (6 things)

1-invade host
2-replicate
3-overcome defense systems
4-spread to other areas via bloodstream
5-replicate
6-exit from host

87

What are the four main routes for invasion and which are the most common two

1- skin
2-mucous membranes
3-transplant
4-mother to fetus
-mucous membranes are the most likely and second would be skin if there were skin breaks

88

What are three modes of transmission

respiratory-sneezing and coughing
GI-fecal and oral
Genital- STDs, homo or hetero

89

What are the two types of infection

localized
general

90

What is localized infection

infection remains near the site of entry

91

What is general infection

infection spreads to 1 or more organs NOT at the site of entry

92

What is the difference in incubation periods for localized vs general

incubation period for localized is shorter than general due to the virus not needing to travel

93

What is the problem regarding incubation periods for general viruses

hard to pinpoint where and when contracted, hard to contain due to long incubation period

94

What are the steps for general infection (6 steps)

1-viruses enter epithelium
2-replicate in epithelium then spread
3-migrate to lymph nodes
4-enter bloodstream (onset of fever and fatigue)
5-enters large organs and replicates
6-enters bloodstream and infects target organ

95

What is viremia

virus dumping into bloodstream

96

What are the main target organs and tissues

skin, buccal mucous membrane, lung, liver, kidney, CNS

97

What is the response for skin infection

skin rash

98

What is the response for buccal mucous membrane infection

rash on inside of cheeks and lips

99

How long is a short incubation period

less than a week

100

How long is a medium incubation period

one to three weeks

101

how long is a long incubation period

months

102

how long is an extra long incubation period

years

103

Why is it important to know the incubation period

diagnosis and tracing outbreaks

104

What is acute virus

nearly immediate

105

What is a non persistent virus

single episode virus

106

What is a chronic virus

continually being produced

107

What is persistent virus

recurring infection due to latency

108

What is acute onset virus

primary infection has symptoms

109

What is reproduction number

the average number of secondary cases caused by a single primary case

110

What is the reproduction number not to be confused with

severity of virus

111

What are the three mechanisms in order to fight infection

1. barrier to infection
2. innate immune system
3. adaptive immune system

112

What is the first line to defense against infection

barriers to infection

113

What are examples of barriers to infection

skin, cilia, pH in stomach

114

What is meant by species resistance

not all viruses infect all species

115

What is innate immunity

quick response with no specificity and no memory

116

What are the 3 components of innate immune system

1. toll like receptors
2. cytokines
3. natural killer cells

117

What are the three cytokines

interferons, chemokines, interleukins

118

When was toll like receptors discovered

1997 in humans

119

How many TLRs have been identified

12

120

How did TLRs get there name

sequence similarity to the toll gene in Drosophila

121

Where are TLRs located

on the cell surface or inside cell

122

Are TLRs specific or general

general

123

How do TLRs when to activate work

when they recognize viral features such as protein spikes, double stranded RNA

124

What are interferons (3 things)

a category of cytokines, small proteins, several different types

125

What produces and secretes interferons

virus infected cells

126

What is the ultimate goal of interferons

to protect neighboring cells from infection

127

Are interferons specific or general

not virus specifc

128

What are interferons specific in

species specific

129

Basic mechanism of interferons (6 steps)

1. virus binds to Toll like receptor
2. cell is stimulated to express IFNs
3. IFNs diffuse out of cell and bind to receptors on neighboring cells
4. activate enzymes that degrade RNA and stop protein synthesis
5. activate natural killer cells
6. enhances adaptive immune response

130

What is the function of natural killer cells

recognize and kill infected cells after the cells have been infected

131

Why don't natural killer cells kill the virus and pathogen

because they are not specific to pathogens and only recognize cells

132

What is meant that cells are recognized as "misisng self"

low levels of MHC

133

What does MHC do

displays the antigens

134

What is the third step of immunity

adaptive immune system

135

Features of the adaptive immune system response

slow, has memory, controlled by phagocytic cells and lymphocytes

136

2 family types of cells involved in adaptive immune response

phagocytic
lymphocytes

137

What are the two cells of the phagocytic cells

dendritic, macrophages

138

What are the two cells of the lymphocytes

b cell
t cells

139

what are the two types of b cells

plasma b cells
memory b cells

140

What are the two types of t cells

helper t cells
cytotoxic t cells

141

What is the function of phagocytic cells

engulf cells or particles recognized as non self and chew up and display those parts on the surface

142

What are cells presenting the antigen called

antigen presenting cells (APC)

143

Where do t cells mature

thymus

144

Where do b cells mature

bone marrow

145

What is the humoral immunity response

antibody mediated
activation of b cells

146

What function do b cells have

produce a very specific type of antibody that will recognize a very specific antigen

147

What causes b cells to reproduce and form an entire population

stimulation from helper t cell

148

What is the main function of plasma b cells

to secrete and release large number of particular antibody into the bloodstream

149

What are the two types of antibodies

IgM and IgG

150

What are IgM antibodies

first to be produced
large multi subunits
DO NOT cross into placenta
sign of recent infection
first time infection

151

What are IgG antibodies

indication of previous infection
longer lasting
cross placenta to fetus
produced in mothers milk

152

What is the role of memory b cells

not used in defense of first infection, prepared for second infection (RAPID response)

153

What do antibodies do

bind to the virus and aggregates them to stop attachment to receptors

154

What are helper t cells function

to recognize and bind to APC that are displaying antigens, stimulates T cell to produce interleukins which stimulate proliferation of B cells and cytotoxic t cells

155

What is the function of cytotoxic t cells

travel through the blood stream recognizing and killing any cells that have the particular antigen on them

156

What are the two types of vaccines

active immunization
passive immunization

157

What is active immunization

antigen is injected into the body to start a response, causes body to produce plasma and memory b cells

158

What is passive immunization

antibodies are injected into a patient to help them fight a current infection

159

What is epidemiology

the study of how diseases affect a community

160

What are the 4 major activities for epidemiology

1. predict disease trends
2.guide control measures
3. evaluate success of control measures
4. aid in diagnosis

161

What is seriological epidemiology

study of the presence of antibodies in the people of a community

162

What is the iceberg concept

antibodies are found in MUCH higher proportion of people than diagnosed with a disease (exposed vs diagnosed)

163

Where is epidemiological info

worldwide: WHO
US: CDC

164

2 methods of viral spread

Person to person
external source

165

3 factors that determine spread of a virus

1- characteristics of a virus
2- characteristics of host
3 characteristics of environment

166

5 characteristics of virus

1- how virus survives outside host
2- virus have alternative host
3-pathogenesis
4- evasiveness of immune system
5- route by which virus is shed

167

Examples of characteristics of the host

age, sex, ethnic group, occupation, nutrition, immunity

168

Characteristics of the environment

geographic location
urban/rural
existence of vectors
socioeconomic status

169

What is prevalence

the proportion of population affected by a disease at a certain POINT

170

What is Incidence

the number of cases of a particular disease recorded over a PERIOD of time

171

What is endemic

refers to a disease that is constantly present at a significant level

172

What is epidemic

an unusual increase in the number of cases within a community "outbreak"

173

What is pandemic

an epidemic involving several continents at the same time

174

What is herd immunity

proportion of people in a population that are immune to a particular virus

175

Two methods to controlling infections

individual and community