Test 1 Flashcards
(175 cards)
1
Q
What is virology?
A
the study of viruses
2
Q
When did the sizes and shapes of the viruses become known?
A
late 1930s
3
Q
Why weren’t the sizes and shapes of the viruses discovered before the 1930’s? What inhibited this?
A
couldn’t see it under a light microscope so they had to wait for the electron microscope
4
Q
What are 4 general characteristics of viruses?
A
- They are SMALL
- Need a LIVING cell
- Have either DNA or RNA genome…but not both
- Have a RECEPTOR BINDING PROTEIN
5
Q
What is the range in size for how small a virus is in diameter?
A
20-150nm
6
Q
Why do viruses need a living cell
A
the virus itself is considered to not be living so it needs a prokaryotic or eukaryotic organism to replicate and survive
7
Q
Why do viruses need a receptor binding protein
A
thats how they bind and infect a cell, the binding protein allows them to get on the surface of a virus
8
Q
What are the 3 main components of a virus
A
- nucleic acid
- protein coat
- may or may not have a lipid envelope
9
Q
What is the one goal of a virus
A
to deliver its genome to host cell which then causes hosts genes to make virus parts
10
Q
How many genes do viruses have
A
at most 10 genes
11
Q
What type of nucleic acid do viruses have
A
DNA or RNA
12
Q
Viral genomes range in size from how many basepairs
A
3000 to 200,000
13
Q
DNA viruses have what type of genome
A
double stranded
14
Q
How are DNA viruses made into proteins (basic steps)
A
transcribed into mRNA
translated into protein
15
Q
What type of genome do RNA viruses have
A
single stranded
16
Q
Which is more stable? DNA or RNA?
A
DNA is more stable due to having double strand
17
Q
Why does RNA change more rapidly than DNA genomes?
A
less stable
in DNA there is excess backtracking and proofreading and repair mechanisms that don’t exist in RNA
18
Q
Why does RNA have the backtracking and repair mechanisms
A
because RNA is an intermediate typically while DNA goes through meiosis and mitosis after being copied
19
Q
RNA genomes can be one of what two things?
A
positive or negative stranded
20
Q
What is different about the steps in positive vs negative stranded RNA
A
positive- directly translated to protein, it is already mRNA
negative-contain complimentary sequence to positive strand (ex. retrovirus)
21
Q
How is a retrovirus translated
A
converted back to DNA and then back into the correct strand of RNA then translated into a protein
22
Q
What type of polymerase do humans have?
A
DNA dependent RNA polymerase
23
Q
What type of polymerase does RNA genome need
A
RNA dependent RNA polymerase
24
Q
Since humans do not have the RNA dependent RNA polymerase, how does the virus get this?
A
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
