Viruses & Other Acellular Entities I Flashcards
1
Q
Viruses have an ________________ stage in their life cycle
A
Acellular
2
Q
Viruses alternate between two states in their life cycles. What are they?
A
The actively replicating state
The virion, a biologically inert structure or a single virus outside of the cell
3
Q
At its simplest, the virion consists of a ______________ of protein molecules and a bit of nucleic acid that can be either DNA or RNA
A
Capsid
4
Q
An ___________________ is an additional membrane that surrounds the capsid
A
Envelope
5
Q
Non-eveloped viruses consist of a ________________ only while an enveloped virus has a phospholipid bilayer membrane with virus-encoded proteins surrounding the ______________
A
Nucleocapsid
Nucleocapsid
6
Q
Virions contain one or more ___________________ of either DNA or RNA, double-stranded or single-stranded
A
Chromosomes
7
Q
Most of the time, viral genomes have all genes on a single nucleic acid, but sometimes the genome is divided among several separate molecules to form a __________________ genome
A
Segmented
8
Q
The basic structure of the genome of a given virus is ______________
A
Constant
9
Q
What is a naked virus?
A
An enveloped virus that has lost its envelope
10
Q
Why are viral genomes generally small?
A
Because they do not encode most of the machinery needed for multiplication - the host cell provides most of the genetic information needed by the virus
11
Q
Virions do not possess genes that contain four things - what are they?
A
- Encode structural proteins of the virus
- Proteins necessary for the replication of viral nucleic acid and virion assembly (not encoded in host genome)
- Regulatory proteins
- Proteins that help progeny viruses escape from host cell
12
Q
The replicating form of the virus requires the combined genomes of ____________ and __________
A
Virion
Host cell
13
Q
Viral capsids are usually ______________
A
Symmetrical
14
Q
There are three types of symmetry in viral capsids. What are they?
A
- A cynlindrical or tubular capsid
- A nearly spherical polyhedral/icosahedral capsid
- A binal capsids (bactiophages)
15
Q
What does “binal” mean?
A
Twofold
16
Q
An icosahedral capsid has ____________ triangular faces
A
20
17
Q
Binal capsids consist of both forms of symmetry: a ___________________ capsid containing nucleic acid is joined to a _____________ tail that functions in injecting nucleic acid into host
A
Icosahedral
Cylindrical
18
Q
How are envelopes obtained?
A
Budding
19
Q
From where does a viral envelope originate?
A
The host phospholipid bilayer
20
Q
The envelope proteins are all __________ encoded
A
Virus
21
Q
How does budding occur?
A
- Membrane proteins are synthesized from viral mRNA on ribosomes bound to the ER and sorted through the Golgi to the cell membrane
- The nucleocapsid binds to the viral envelope proteins in the membrane and buds off
22
Q
Viral budding can occur on the cell membrane or the ____________ membrane or _______, in which case the virion winds up in the lumen of the ER
A
Nuclear membrane
ER
23
Q
Virus multiplication is a ___-stage process
A
Five
24
Q
What are the five steps of virus multiplication?
A
Attachment
Penetration
Macromolecular synthesis
Assembly
Release
25
What occurs during attachment?
The virion binds to the host cell using surface proteins that bind to specific structures on the host cell surface
26
What occurs during penetration?
The viral nucleic acid and sometimes some of its proteins gain access to the site at which the nucleic acid will be expressed and replicated
27
What occurs during macromolecular synthesis?
The viral nucleic acid is replicated and viral proteins, including capsid proteins, are made
28
What occurs during assembly?
Capsid proteins and viral nucleic acid are assembled into nucleocapsids
29
What occurs during release?
The complete virions are released from the infected cell. If the virus is enveloped, the envelope is acquired at this stage
30
The attachment of a virion to its host cell is highly \_\_\_\_\_\_\_\_\_\_\_
Specific
31
How do virions attach to the host cell?
Via noncovalent interactions between one of their capsid or envelope proteins and a protein or carbohydrate on the surface of the host cell
32
Interactions between a virion and host cell require a close match of _____________ and \_\_\_\_\_\_\_\_\_\_\_\_\_\_
Shape
Charge
33
Why do most virions never encounter a host cell with the right chemical structures on its surface?
Because attachment is largely a chance event; if a virion does not find a suitable host, it is eventually inactivated in the environment by proteases and nucleases or accumulation of mutations in their nuclei acids
34
Bacteriophage injection is by ____________ \_\_\_\_\_\_\_\_\_ injection
Nucleic acid
35
Viruses of bacteria and archaea face the problem of getting their nucleic acid across the thickened or multilayered cell envelope. How does their structure address this need?
The binal viruses typically have a contractile tail with an inner core that penetrates through the cell wall when the tail sheath contracts. The nucleic acid then moves through the hollow core into the cytoplasm
36
Do the capsids of bacteriophages enter the host cell?
No, they cannot; hence they developed a binal structure
37
How does penetration occur in enveloped viruses?
Membrane fusion followed by uncoating
38
How do unenveloped viruses enter the host cell?
Endocytosis
The acidic pH of the endosome then causes conformational changes in the capsid proteins, causing pores to form
39
What are the five steps of penetration and uncoating of an enveloped virus in an animal cell?
1. Viral envelope fuses with the cell membrane
2. Phagocytosis occurs, and the envelope fuses with the endosome membrane
3. The nucelocapsid is released into the cytoplasm
4. Uncoating may occur in the cytoplasm and releasing the viral nucleic acid or
5. The nucleocapsid may be transported into the nucleus for uncoating
40
How do plants become infected?
Plant viruses penetrate via wounds or by insects
41
How are plant viruses transmitted from cell to cell within the same plant?
Via plasmodesmata
42
How do viral nucleic acids move from plasmodesmata?
By special viral proteins that actively move the nucleic acid through the plasmodesmata powered by ATP hydrolysis
43
In general where do DNA viruses of eukaryotic cells replicate?
In the nucleus
44
In general where do RNA viruses of eukaryotic cells replicate?
The cytoplasm
45
What exceptions exist regarding where DNA and RNA viruses replicate?
Pox viruses are DNA viruses that replicate in the cytoplasm
Influenza and retroviruses are RNA viruses that replicate mostly within the nucleus
46
How do DNA phages often replicate their genome?
Rolling circle mechanism
47
What must occur in the lambda phage before rolling circle replication can occur?
Circulization of the chromosome:
The lambda chromosome is linear but has single-stranded ends that are complementary to each other, which allow the chromosome to circularize. Ligases from the host cell then seal the nicks
48
How does rolling circle replication occur in lambda phage?
1. A nick is made on one strand
2. Leading strand synthesis begins using the intact circular strand as the template
3. Lagging strand synthesis follows shortly afterwards
4. Because the template is circular, synthesis can continue indefinitely, producing a long concatemer
49
What is a concatemer?
An increasingly long tail of DNA that consists of many lambda chromosomes covalently joined end to end
50
What is a positive sense virus?
If the genome of a virus can enter the cell and immediately be recognized by the host cell's ribosome, it is positive sense; in other words, the virus doesn't require it's own helicase
51
What is the final step in lambda DNA replication?
A specific viral enzyme cleaves the concatemer into individual chromosomes by making staggered nicks in the specific sequences that mark the ends of the linear chromosome
52
The chromosome of (\_\_) strand RNA viruses act as mRNA to produce a replicase
(+)
53
Single-stranded RNA viruses are conventionally divided into two types. What are they?
Positive strand viruses have a chromosome that has the same base sequence as viral mRNA
Negative strand viruses have a chromosome with a sequence complementary to the mRNA
54
Why does a positive strand RNA virus *not* require its own helicase to initiate translation?
Because positive strand RNA viruses have ribosome binding sites that are recognized by ribosomes in the cytosol; once translated, a viral RNA replicase is made that will replicate the RNA
55
Genomes of viruses can be one of six types. What are these six types?
dsDNA
ssDNA
dsRNA
+ssRNA
-ssRNA
Retrovirus
56
What does the chromsome of a positive strand RNA virus function as?
It acts as a mRNA to produce RNA replicase
57
What must enter the host cell along with a negative strand ssRNA or double-stranded RNA virus?
A replicase
58
What is the initial product of the RNA replicase of a positive strand ssRNA virus?
A number of RNA strands complementary to the chromosome. These negative strands are then used as templates to produce the progeny positive strand chromosomes
59
Why must negative strand ssRNA and dsRNA viruses have replicases enter host cells?
Their host cells do not have any RNA replicases
Their chromosomes are unable to act directly as mRNA molecules to direct the synthesis of a RNA replicase
60
Once the chromosome and RNA replicase enter the cell, how does replication begin for negative strand ssRNA and dsDNA viruses?
The replicase uses the negative strand as a template to produce a series of positive strands which then act as mRNA to produce more replicase
61
What do the positive strands do for negative ssRNA and dsRNA viruses?
Templates for the production of progeny negative strand chromosomes or double-stranded ones
62
Norovirus is a nonenveloped ___________ virus
+ssRNA
63
How many genes does Norovirus have?
8 to 9 known genes
64
To what does Norovirus bind?
Human histo-blood group antigens and others
65
Where does Norovirus act?
In the GI tract
66
How does Norovirus spread?
Fecal to oral route, although it can be aerosolized in vomit
67
The chromosome of ___ strand RNA viruses can act as mRNA to produce a replicase
(+)
68
What are the steps in the replication of a (+) strand RNA virus?
1. (+) strand RNA chromosome can act as mRNA
2. Translation of (+) strand produces a RNA replicase
3. RNA replicase makes a (-) strand RNA complementary to the (+) strand
4. The (-) strand can then be used as a template to produce daughter copies of the (+) strand chromosome
69
What are examples of + ssRNA viruses?
Norwalk virus (Norovirus)
Rhinovirus (cold)
West Nile virus
Dengue
Hepatitis C and Hepatitis E
Coronavirus (SARS, MERS)
70
A ________________ enters the host cell along with the chromosome of (-) strand RNA viruses and double-stranded RNA viruses
Replicase
71
What is the replication strategy in(-) strand RNA viruses?
1. (-) strand and ds strand RNA viral chromosomes cannot act as mRNA; their chromosomes enter the host cell with a molecule of RNA replicase
2. The RNA replicase makes a (+) strand mRNA
3. (+) strand RNA makes more replicase and other viral proteins
4. (+) strand RNA also acts as a template for replicase to produce more (-) strand chromosomes or ds chromosomes in the case of dsRNA viruses
72
One group of ssRNA viruses, the \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, has a unique method of replication. Their RNA is (+) strand, but instead of acting as mRNA, theirs is converted into dsDNA by the enzyme reverse transcriptase
Retroviruses
73
What is reverse transcriptase?
A virally encoded enzume that enters the host cell; it uses ssRNA as a template to produce a complementary ssDNA molecule, simultaneously degrading the RNA; the ssDNA is used as a template to make dsDNA, which is then transported into the nucleus, where it is integrated into the host chromosome
74
Why integrates retroviral DNA into the host genome?
Integrase
75
What is integrase?
An enzymatic protein that catalyzes the insertion of viral dsDNA into the host genome
76
What ultimately translates the integrated provirus to produce ssRNA viral chromosomes and mRNA for viral proteins?
The host cell RNA polymerase
77
What are some examples of (-) ssRNA viruses?
Ebola
Influenze
Rabies
Mumps
Meales
Hantavirus
78
What are two examples of dsRNA viruses discussed in class?
Rotavirus
Bluetongue virus
79
What does rotavirus cause in infants?
Diarrhea
80
Estimates say that approximately \_\_% of hospital visits by infants with diarrhea are caused by Rotavirus, a type of \_\_\_RNA virus
50%
dsRNA virus
81
How many infants and small children die each year from Rotavirus across the globe?
500,000
82
What does Blutongue virus infect?
Ruminants (i.e., cows)
83
What are the mortality rates of Bluetongue virus?
2 to 90%
84
How is Rotavirus transmitted?
Fecal to oral
85
Is Bluetongue virus contagious?
No; it is spread by insects
86
What cells does HIV infect?
CD4(+) T-cells
87
HIV is a type of \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Retrovirus
88
What happens once HIV binds to a suitable host?
Attachment and coreceptor binding
89
Upon coreceptor binding to HIV, a conformational change occurs that enables proteins on HIV to embed into the membrane. What do these proteins do that facilitates the fusion of HIV with the host cell?
They bend, bringing HIV and host cell close enough for fusion
90
Upon entering the cell, HIV capsid breaks open, and 5 macromolecules are released into the host cell. What are they?
1. RNA strand 1
2. RNA strand 2
3. Integrase
4. Protease
5. Reverse transcriptase
91
Reverse transcriptase has two catalytic domains. What are they?
Ribonuclease domain
Polymerase domain
92
What does the polymerase domain of reverse transcriptase do?
Takes viral ssRNA and transcribes it into a ds RNA-DNA hybrid helix
93
What domain of reverse transcriptase breaks down the RNA of the ds RNA-DNA hydrid helix?
Ribonuclease
94
After the RNA is degraded by the ribonuclease domain, what does polymerase do with the remain viral DNA?
It makes a double stranded DNA
95
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ cleaves dinucleotides from the 3' end of the viral dsDNA, creating "sticky ends," and transfers this "sticky" dsDNA into the nucleus where it facilitates the integration of the viral DNA into the genome
Integrase
96
The host cell transcribes proviral DNA to mRNA; viral mRNA migrates into the cytoplasm. Some mRNA molecules must be cleaved by ______________ to be infectious.
Protease
97
Two viral RNA strands, \_\_\_\_\_\_\_\_\_\_\_\_\_, protease, and reverse transcriptase come together in the host cell; a capsid reforms; and the HIV virus leaves the cell, becoming enveloped
Integrase
98
What are the general steps for replication in retroviruses?
1. Envelope fusion and uncoating introduces ssRNA chromosome and two enzymes - reverse transcriptase and integrase - into the cytoplasm
2. Reverse transcriptase makes DNA complement to RNA, degrading the RNA
3. Reverse transcriptase makes dsDNA from the ssDNA
4. The dsDNA version of the chromosome is transferred to the nucleus
5. Integrase inserts the retroviral provirus into the host chromosome
6. Transcription of the provirus produces (+) strand version of the chromosome
7. After splicing, the RNA transcripts can at as mRNA to produce viral proteins
8. If unspliced, the transcript can be used as a chromosome for progeny virions
99
What are some examples of dsDNA viruses?
Adenoviruses
Herpesviruses
Poxviruses
100
Chicken pox is what type of virus?
A herpes virus
101
What are some examples of ssDNA viruses?
Parvovirus
102
What are two types of parvovirus discussed in class?
Parvovirus B19 (Fifth Disease or Slapped Cheek disease)
Canine parvovirus
103
Parvovirus B19 infects humans but is normally \_\_\_\_\_\_\_\_\_\_\_\_\_\_, although it can be dangerous to an unborn baby as it can cross the \_\_\_\_\_\_\_\_\_\_\_\_\_\_
Self-limiting
Placenta
104
Canine parvovirus results in an infection of the _____ \_\_\_\_\_\_\_\_\_\_; it is potentially life-threatening and very contagious to other dogs
GI tract
105
Is viral protein synthesis regulated?
Yes
106
Viral multiplication requires the synthesis of ___________ \_\_\_\_\_\_\_\_\_\_\_\_
Viral proteins
107
What types of viruses can self-assemble if the their constituent parts are in high enough concentration?
Simple-shaped viruses, like the tobacco mosaic virus
108
Most viruses make several proteins with only one function: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
The regulation of timing synthesis of other proteins
109
Eukaryotic viruses often make _________________ that need to be cleaved
Polypeptides
110
Why are polycistronic messages common in bacterial viruses?
Because bacterial ribosomes bind to a particular sequence of bases; as many polypeptides can be made as there are ribosome binding sites on the mRNA adjacent to start codons
111
Why are polycistronic messages not possible in eukaryotic viruses?
Because eukaryotic translation machinery uses an initiation factor that recognizes the 5' cap on mRNA; there is only one site at which ribosomes can bind
112
How do eukaryotic viruses get around the limitations of eukaryotic ribosome translation?
With polycistronic mRNA that contain a transcript of multiple genes but lack stop codons; thus ribosomes make multiple proteins that are linked by peptid ebonds that must be cleaved into individual proteins
113
Provide an overview of synthesis and cleavage of a polypeptide in a eukaryotic virus.
1. Ribosome binds at the 5' cap
2. Polycistronic mRNA made by viruses of eukaryotes lack stop codons at the ends of all but the last genes
3. Translation occurs and produces a polypeptide with separately folded domains corresponding to each gene
4. The unfolded linker regions are highly suspectible to protease cleavage
5. Protease cleavage results in individual proteins
114
Capsid assembly and nucleic acid packaging are tightly _____________ processes
Linked
115
In ____________ \_\_\_, capsid assembly begins nearly simultaneously with replication, and the cleavage of the ________________ of DNA occurs as the DNA enters the capsid
Phage lambda
Concatemer
116
In phages besides phage lambda, packaging occurs by a __________ \_\_\_\_\_\_\_\_\_\_\_\_
Headful mechanism
117
What is headful packaging?
Phage DNA from a concatemer enters the empty head until the head is full; the DNA is cleaved and head assembly completed
118
Two examples of headful packaging mechanisms discussed in class were of ______ and ____ phages
T4 bacteriophage
Theta29 phage
119
Nucleic acid packaging requires host \_\_\_\_\_\_
ATP
120
Assembly of simple viruses occurs \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_; more complex viruses have regulated assembly pathways
Spontaneously
121
How are nonenveloped virions released?
Lysis of the host cell
122
Which causes more damage to the cell upon release: enveloped or non-enveloped virions?
Enveloped virions as release is a continuous process
123
What are the three major tactics of viral infection?
1. Hit and run
2. Latency with occasional reemergence
3. Slow and low
124
What tactic of viruses involves a large burst and rapid clearing with enough progeny (hopefully) to find a new host?
Hit and run approach
125
What tactic do influenza and Norwalk virus use?
Hit and run
126
What type of virus usues the latency with occasional reemergence tactic?
Herpes
127
What tactic utilizes a low level of continuous shedding?
Slow and low
128
What virus utilizes the slow and low tactic?
Spumavirus (foamy viruses)
129
What usually involves the integration of the viral chromosome into the host chromosome but in whicn the viral chromosome does not actively replicate itself?
Latency
130
Because of the way in which latency works, what type of viruses are capable of latency?
DNA viruses
131
What do we usually refer to as latent bacteriophages?
Temperate phages
132
What is an integrated viral chromosome called?
Prophage
133
A host cell that carries a phage in the latent state is termed \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.
Lysogenic
134
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ make their host cells immune to subsequent infection by another virion of the same kind
Prophages
135
How do prophages make their host cells immune to subsequent infection by another virion of the same kind?
Via a repressor protein made by the provirus; this protein prevents the expression of the provirus genes required for lytic growth
136
What can be induced to reenter active multiplication?
Proviruses
137
What often triggers a provirus to reenter active multiplication?
Stress
138
The process whereby a trigger stimulates a provirus to reenter active multiplication is called _________________ for a phage or ____________________ for animal viruses
Induction
Reactivation
139
During latency, do viruses actively replicate?
No; however, their genomes are passively replicated every time the host chromosome is replicated as they have integrated their genome with that of the host
140
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ is a strategy for intergenerational transmission
Latency
141
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ and then reactivation is an evolutionary mechanism for delaying virion production in some infected hosts to ensure transmission among generations.
Latency
142
A ___________________ bacteriophage has both lytic and lysogenic cycles
Temperate
143
T4 bacteriophage, which infects *E. coli*, undergoes what type of replication cycle: lytic or lyosgenic?
Lytic
It constantly produces virions and ultimately leads to cell death
144
What are the major differences between the lytic and lysogenic cycle?
Both cycles are methods of viral reproduction. Both cycles involve the introduction of the virus into a cell to use the cell's genetic material to replicate more viruses. The key difference is that in the lytic cycle the viral DNA is maintained in a separate pocket from the cellular DNA and matures separately while in the lysogenic cycle the viral DNA is kept mixed with the celluar DNA. Another key difference is that in the lytic cycle the viruses replicate constantly which results in the eventual lysis, or death, of the host cell to release the new viruses while in the lysogenic cycle the virus replicates only with the regular cellar mechanism for reproduction and is only released through some separate outside event.
145
To what receptors does T4 bacteriophage bind?
OmpC
LPS
The T4 virus initiates an *Escherichia coli* infection by binding OmpC porin proteins and lipopolysaccharide (LPS) on the surface of E. coli cells with its long tail fibers (LTF)
146
Does the lambda phage undergo lytic or lysogenic replication?
Both
147
To what receptor does lambda phage bind?
LamB receptor
148
What is a LamB receptor?
Maltoporins (or LamB porins) are a family of outer membrane proteins that import maltose and others
149
When is a lysogenic cycle likely to occur in a host cell?
When the host cell is happy and fat
150
What protein is the first to be transcribed and translated upon infection of lambda phage?
Cro
151
What is Cro?
A transcriptional repressor that prevents lambda phage for undergoing lytic replication
152
What happens to Cro when a host cell is stressed?
A protease will chew up Cro, and lambda phage genes will be expressed, changing from the lysogenic to lytic cycle
153
Cro is a type of _______________ repressor
Transcriptional
154
When T4 bacteriophage infects a cell, what is immediately expressed?
An endonuclease
155
Why facilitates the lytic cycle of T4 bacteriophage?
The immediate expression of an endonuclease that chops up the host cell DNA
156
In some lysogenic host cells, gene products based on \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_-\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ transcripts can accumulate and lead to latency
Latency-associated transcripts
157
In some host cells, gene products based on latency-associated transcripts can accumulate and lead to latency; if transcription is shifted to the lytic products, what will occur?
A new virus is produced that will usually lead to cell death
158
What is the name of the herpes virus?
*Herpesviridae*
159
What type of virus is *Herpesviridae*?
A linear dsDNA virus
160
How many genes make up *Herpesviridae*?
100 to 200 genes
161
HSV-1 is _________ herpes, generally infecting the mouth.
Orolabial
162
HSV-2 is ___________ herpes, typically infecting the genitalia and rectum.
Genital
163
Is chicken pox and shingles a Herpes virus?
Yes
164
*Varicella zoster* virus is also know as what?
Chicken pox
Shingles
165
The virus that causes mononucleosis and associated with several types of cancers is a herpes virus called _________________________ (HHV-4)
Epstein-Barr virus
166
Do herpes viruses undergo a latency period?
Yes
167
During latency of herpes, most of the genome is transcriptionally \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_; it circularizes and associates with histones; and it is copied by cell ddDNA polymerase during mitosis.
Silent
168
During the lytic phase of herpes, what polymerase copies the genome: host cell or virus?
Viral ddDNA polymerase copies the genome
169
What two things can stabilize latency of the herpes virus?
Epigenetics
Methylation programs
170
What early viral gene seems to play a role in latency of herpes?
VP16
171
What happens when VP16, an early viral gene of herpes virus, fails?
Latency
172
The site of ________________ infection plays a role in the latency of herpes.
Neuronal
173
When a herpes virus infects the distant part of the neuron, what phase is favored?
Latency
174
When a herpes virus infects the cell body, what phase tends to be favored?
Lytic
175
How are viruses classified?
Into artifical groups based on molecular biology, "life" cycles, and host organisms
176
Viral taxonomy gives us information about the structure of viruses' ___________ \_\_\_\_\_\_\_\_\_\_\_s, but no direct information about their relatedness.
Nucleic acids
177
What acellular entites consist of a single type of macromolecule that is replicated by host cells?
Viroids
Prions
178
What are viroids?
Viroids consist of unencapsulated, or naked, RNA that infects several species of plants; the RNA is a circular single strand
179
Because there is a great deal of internal complementarity to viroid RNA, what happens to its single-stranded nature?
The single strand hydrogen bonds with itself to form a rigid rod
180
Although viroids differ in size, all are in the ___ to ___ base range.
250 to 400
181
How are viroids transmitted from plant to plant?
By insects
182
How are viroids transmitted from cell to cell within a plant?
Plasmodesmata
183
Is viroid RNA translated?
No
184
How is viroid RNA replicated?
Rolling circle mechanism
185
How do viroids replicate via rolling circle mechanism?
1. Host machinery uses rolling circle mechanism to produce a concatemer of RNA complementary to viroid RNA
2. This concatemer is cleaved into monomeric lengths of RNA that circularize
3. These circular complementary RNA molecules act as templates for second round of rolling circle synthesis, concatemer cleavage, and circularization to produce progeny viroids
186
Where does the family *Pospiviroidae* replicate?
Nucleus
187
Where does the family *Asunviroidae* replicate?
Chloroplasts
| (RNA has ribozyme activity)
188
What are prions?
Aberrant conformations of normal mammalian brain protein that replicate by catalyzing conformational changes in normal proteins
189
What is the best known case of prion infection?
BSE
Bovine spongiform encephalopathy
190
How does bovine spongiform encephalopathy spread?
It appears spontaneously in a very low percentage of animals
It became a problem in modern agricultural systems that supplemented cattle feed with ground up offal from slaughterhouses (i.e., cows ate other cows); this allowed the disease to become contagious
In New Guinea, a similar disease developed because of ritual cannibalism
191
What human disease results from eating beef contaminated with bovine spongiform encephalopathy?
new variant Creutzfeldt-Jakob disease (nvCJD)
192
A prion is a normal protein gone rogue - it shares the same amino acid sequence of normal proteins but differs in its __________________ structure.
Tertiary structure
3D form
193
What do prions catalyze?
In the variant conformation, prions catalyze the switch of all the normal protein into the variant conformation
194
What happens as variant conformations build up?
They aggregate into long rods, which are released when the cell dies, and the abnormal protein then perpetuates the process in adjacent cells
195
What does PrP stand for?
Prion protein - one suspectible to becoming a prion
196
What does scPrP stand for?
Scrappy prion protein - an infectious prion protein
197
How many types of influenza are there?
Three
198
What are the three types of influenza?
Type A
Type B
Type C
199
Type ___ influenze is divided into subtypes based on H(17) and N(10)
Type A
200
Which type of influence infects animals including birds and pigs?
Type A
201
What type of influenze is not subdivided into subtypes?
Type B
202
What influenza type is found only in humans?
Type B
203
What type of influenza is the mildest type and infects humans and pigs?
Type C
204
For Type A influenza, what do H and N stand for regarding its subtypes?
H is for hemagglutinin
N is for neuraminidase
205
For influenza virus Type A, "H" is the _______________ protein, which binds to sialic acid attached to galactose by an alpha2--\>6 linkage.
Hemagglutinin protein
206
To what does hemagglutinin bind?
Sialic acid
207
The sialic acid hemagglutinin protein binds is attached to ____________ by an alpha(2,6) linkage.
Galactose
208
Where is most sialic acid found in the human body?
Respiratory epithelial cells
209
Why is it so difficult for the avian flu to infect humans?
Sialic acid bound to galactose via an alpha(2,3) linkage
210
Where is the avian flu found in ducks?
The gut
211
In influenze virus Type A, "N" refers to __________________ protein, which is important for viral release.
Neuraminidase protein
212
How does Type A influenze spread?
Water droplets from sneezing, coughin, and talking that land in the mouth of a nearby unfortunate person
Touching contaminated surface and then eyes, mouth, or nose
213
You should be familiar with the structural diagram of the influenza virus.
214
What are the symptoms of influenza?
Fever, feeling feverish and/or chills
Cough
Sore throat
Runny/stuffy nose
Muscle/body aches
Headaches
Fatigue
Vomiting and diarrhea
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Does everyone with the flue have a fever?
No, not everyone with the flu will have a fever
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What constitutes a fever in Georgia?
Over 100 degrees Farenheit
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What symptoms are required for an influenza-like illness (ILI) in Georgia?
1. Fever above 100 degrees Farenheit
2. Cough and/or
3. Sore throat
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Which flu symptom is more common in children than adults?
Vomiting and diarrhea
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How can you tell the difference between the flu and a cold?
You cannot; only a test can ultimately distinguish between the two
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Although only a test can definitively determine whether a person has a flu or cold, what are some ways to tell the two apart?
People with colds are more likely to have a runny nose
People with the flu are more likely to have more intense and frequent symptoms
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What is the period of contagiousness for the flu?
You are contagious as early as 1 day before you develop symptoms and up to a week after you become sick
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When is flu season?
It varies, but it can begin as early as October and as late as May
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Who should receive the flu vaccine?
The CDC recommends the flu vaccine for everyone over 6 months
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Which people are recommended *against* getting the flu vaccine?
People with allergies or Guillain-Barre syndrome or are currently ill
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What is Guillain-Barré syndrome?
Guillain-Barré syndrome (GBS) is a rare neurological disorder in which the body's immune system mistakenly attacks part of its peripheral nervous system—the network of nerves located outside of the brain and spinal cord
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What cause Guillain-Barre syndrome?
Most cases usually start a few days or weeks following a respiratory or gastrointestinal viral infection. Occasionally surgery will trigger the syndrome. In rare cases vaccinations may increase the risk of GBS. Recently, some countries worldwide reported an increased incidence of GBS following infection with the Zika virus
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When should people get the flu vaccine?
In September or whenever it becomes available
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What are two ways the flu vaccine administered?
Injection
Spray
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The regular flu shot is given how?
Via intramuscular injection
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The high-dose flu shot is given to people over the age of \_\_\_\_\_\_\_\_\_\_.
64
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The high-dose flu shot is given to older people or people with compromised immune systems. How is it administrated?
Via intradermal injection
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People allergic to what type of eggs can have an allergic reaction to the flu vaccine?
Chicken eggs
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How is the flu vaccine produced?
The strain picked is put into chicken eggs where it reproduces and is then inactivated for administration
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How are flu vaccines made for people allergic to chicken eggs?
Via cell culture
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For people with severe allergies to chicken eggs, how is the flu vaccine developed?
By using a recombinant virus only infectious to insects
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What is the flu vaccine spray made of?
Live attenuated influenza
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Who may receive the spray flu vaccine?
Health people between the ages of 2 and 49 who are not pregnant
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Why is the flu vaccine spray not recommended for this season?
Past ineffectiveness
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What are the two current flu vaccines?
Trivalent flu vaccines (HA)
Quadrivalent flu vaccines
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What are the 6 options available to people for the flu vaccine?
1. Standard dose shots given into the muscle (most) or skin
2. High-dose shots for older people
3. Shots made with adjuvant for older people
4. Shots made with virus grown in cell culture
5. Shots made using a vaccine production technology (recombinant vaccine) that does not require use of the flu virus
6. Live attenuated influenze vaccine (LAIV) (temperature sensitive)
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What is an adjuvant vaccine?
An adjuvant is an ingredient used in some vaccines that helps create a stronger immune response in people receiving the vaccine. Adjuvants help the body to produce an immune response strong enough to protect the person from the disease he or she is being vaccinated against
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What three general types of antivirals are available for the flu?
Neuraminidase inhibitors
Polymerase acidic inhibitors
Proton channel inhibitors
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What are the three neuraminidase inhibitors available for the flu?
Tamiflu
Relenza
Rapivab
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How is Tamiflu (Oseltamivir) given?
Orally
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How is Relenza (Zanamivir) given?
Inhalation
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How is Rapivab (peramivir) given?
IV
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What is the name of the polymerase acidic protein inhibitor available?
Baloxavir (xofluza)
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How is Xofluza (Baloxavir) given?
Orally
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How does Xoflusa (Baloxavir) work?
It is a polymerase acidic protein inhibitor.
Polymerase acidic protein finds mRNA from host, captures and cleavesthe first 10–20 nucleotides of 5′ capped host mRNAs, uses these snippets as primers, and elongates viral RNA
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What is polymerase acidic protein (PA)?
It plays an essential role in viral RNA transcription and replication by forming the heterotrimeric polymerase complex together. The complex transcribes viral mRNAs by using a unique mechanism called cap-snatching. It consists of the hijacking and cleavage of host capped pre-mRNAs. These short capped RNAs are then used as primers for viral mRNAs. The PB2 subunit is responsible for the binding of the 5' cap of cellular pre-mRNAs which are subsequently cleaved after 10-13 nucleotides by the PA subunit that carries the endonuclease activity
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What is cap snatching?
It consists of the hijacking and cleavage of host capped pre-mRNAs. These short capped RNAs are then used as primers for viral mRNAs. A polymerase complex subunit is responsible for the binding of the 5' cap of cellular pre-mRNAs, which are subsequently cleaved after 10-13 nucleotides by the PA subunit that carries the endonuclease activity
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The PA subunit contains ______________ activity.
Endonuclease
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When should an antiviral for the flu be given?
Ideally within 48 hours
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How do Symmetrel (Amantadine) and Flumadine (Rimantadine) work?
They inhibit a proton channel required for "unpacking" the flu into the host cell
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What antivirals for the flu only work on Type A?
Symmetrel (amatadine)
Flumadine (Rimantadine)
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What are some complications of the flu?
Bacterial pneumonia, ear infection, sinus infection, dehydration, worsening of chronic medical conditions, like congestive heart failure, asthma, and diabetes
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Who is most at risk for the flu and complications?
Children younger than five
The elderly
Pregnant women
Immunocompromised
People with certain conditions (asthma, diabetes, blood disorders, kidney disorders, liver disorders)
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How can you prevent acquiring and spreading the flu?
Avoid close contact
Stay home when sick
Cover mouth and nose when coughing and sneezing
Clean hands with soap and water (prefered) or alcohol sanitizer
Don't touch your eyes, nose, mouth
Be healthy (sleep, nutrition, fluids, clean frequently touched surfaces)
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When is an influenza outbreak considered "active" in an area?
When doctors' visits for influenza-like illnesses begin to increase compared to baseline; baseline levels are considered to be between 0 and 3 percent
