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Module 9: Viruses (Viral Characterization) Flashcards

1
Q

Virus

A

Small acellular/sub-cellular particles that consist of a DNA or RNA genome surrounded by a protein coat that can replicate ONLY in living host cells

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2
Q

What are the 3 basic parts of a virus?

A

1) RNA or DNA genome
2) Capsid
3) Viral Envelope

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3
Q

Capsid

A

A protective protein shell that surrounds the genome of a virus

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4
Q

Viral Envelope

A

A host-cell derived membrane that surrounds the capsid of certain viruses (Not all viruses have it!)

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5
Q

Nucleocapsid

A

The viral genome AND the viral capsid (the unit as a whole)

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6
Q

Due to viral dependence on host cells, viruses MUST have methods of what? (2)

A

Methods of getting INTO the host cell and then getting OUT of it

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7
Q

What overall is the host cell needed for?

Viruses mainly depend on host cell enzymes for what? (3)

A

Overall = For production of new viral particles

1) Translation (ALL viruses rely on host components for this)

2) Transcription (SOME viruses rely on host enzymes for this)

3) Genomic Replication (ALL viruses)

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8
Q

Viruses infect what forms of life?

A

ALL of them

(Plants, animals, fungi, bacteria, archaea)

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9
Q

How long has the science of virology been around for?

A

Roughly 120 years

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10
Q

What did Dimitri Ivanovski find?

A

1892 –> Discovered a disease in Tobacco that could be transmitted even through a filter small enough to exclude the smallest known bacteria

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11
Q

What discovery was seen as the official beginning of virology?

(Who discovered it?)

A

(1898 Martinus Beijernik)

Discovered the infectious agent causing disease in tobacco plants (earlier discovered by Dimitri Ivanovski) and called it a “soluble living germ”

== tobacco mosaic virus

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12
Q

Who discovered the cause of Yellow Fever?

A

Walter Reed (1901) –> Discovered Yellow Fever is caused by a virus transmitted by mosquitoes

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13
Q

Who were the first to describe bacteriophages for the first time?

A

Frederick Twort and Félix d’Hérelle

(1910)

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14
Q

What did Martinus Bejernik describe the TMV as in his discovery?

A

a “soluble living germ”

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15
Q

What is the typical diameter of a viral particle

A

10-100 nm

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16
Q

How long is Poliovirus?

A

~ 30 nm

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17
Q

How long is Poxvirus?

A

~ 200 nm long

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18
Q

What are the defining common characteristics of viral genome? (3)

A

1) Type of nucleic acid (dsDNA, dsRNA, ssDNA, ssRNA)

2) Most commonly have a CIRCULAR genome (but some can have segmented)

3) Usually a SMALL genome

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19
Q

What is the typical size of a viral genome?

A

Usually small:

From a few thousand nucleotides to 200,000 nucleotides (largest known)

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20
Q

What type of viruses are an exception to the typical genome size of viruses?

A

Giant Viruses (most infect amoebas)

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21
Q

Most giant viruses contain genes that encode for what uncommon product (in viruses)?

A

Translation Enzymes! (aminoacyl-tRNA-synthases)

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22
Q

What is the capsid made up of?

A

Symmetrically arranged capsomeres (capsid protein subunits)

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23
Q

Capsomere

A

A subunit of a viral capsid

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24
Q

Each capsomere consists of…

A

1 or more polypeptides

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25
All viral capsids exist in what morphologies?
1) Helical 2) Icosahedral 3) Combo
26
Helical Morphology
Shape in which capsomeres form a helix and the capsid resembles a hollow tube
27
What factors contribute to forming the helical capsid morphology?
Interactions between individual capsid proteins with the viral genome at regular intervals AND interactions between capsid proteins themselves
28
What is the simplest structural arrangement of a helical morphology?
When a single polypeptide directly coats the genome in a repetitive manner
29
What is the capsid and overall morphology of TMV ?
--> Capsid morphology = Helical --> Overall morphology = Rod shaped/fiber-like
30
What is the nucleocapsid structure of Influenza virus? (Genome + capsid structure
Has 8 separate nucleocapsids! --> Genome = Segmented RNA genome (8 segments) --> Capsid = Helical around each genome segment --> NOTE: Has a viral polymerase bound to the bottom of the nucleocapsid
31
In ALL helical viruses, what is the nature of the relationship between the genome + capsid proteins?
There is a STRONG/INTIMATE association between the genome and the capsid proteins!
32
Most helical viruses have what kind of genome?
ssRNA genome
33
Why do ssRNA genome viruses tend to have helical capsid morphology?
Because ssRNA is pretty unstable; directly coating the genome with capsid proteins helps protect the genome from degradation
34
What is the main difference between plant/bacterial helical viruses and animal helical viruses?
Plant/Bacterial = Nucleocapsid IS the virion Animal = Nucleocapsid is enveloped!
35
In helical viruses, what determines the size of the virus? Why?
The size of the genome! Because the capsid proteins faithfully coat the entire genome, there is no restriction to the size
36
Which has more diversity in virion size: Icosahedral or helical?
HELICAL has > size diversity (Because not limited by the capsid! Icosahedral virions are limited in size by the capsid which has to have a specific # of capsid proteins to achieve the proper shape)
37
Icosahedral Morphology
Capsid shape in which capsomeres form an icosahedron (20-sided polygon) with EACH capsomere making up one face of the polygon
38
In icosahedral viruses, what is each face of the polygon made of?
1 face = 1 capsomere
39
How many polypeptides much east capsomere of an icosahdedral capsid be made of? Why?
Must be made of **at LEAST 3** polypeptides! (Because the globular capsid proteins need to be configured into the proper triangle shape)
40
The smallest icosahedral capsid requires how many capsid proteins?
60 capsid proteins
41
How many axes of symmetry do icosaheddral viruses have? What are they?
They have 3 axes of symmetry: 1) 2-fold axis 2) 3-fold axis 3) 5-fold axis
42
What determines the size of an icosahedral virus?
The size of its capsid! (Only a defined amount of space is available within the capsid because of packaging constraints imposed by the shape + # of proteins needed to make it)
43
How many faces and vertices does an icosahedron have?
20 faces + 12 vertices
44
What is complex morphology? What viruses exhibit this structure?
Structure with multiple types of symmetry (morphology) --> Mainly found in bacteriophages
45
What is the morphology of bacteriophages?
Complex morphology that is a combination of: Head = Icosahedral Tails = Helical
46
In terms of a viral envelope, viruses can either be...
1) ENVELOPED 2) NAKED (non-enveloped)
47
Non-Enveloped Virus
Complete virion that consists of only a nucleocapsid (no envelope) AKA "Naked"
48
Enveloped Virus
A virion with a host-cell derived membrane (AKA viral envelope) that surrounds the nucleocapsid
49
What are examples of non-enveloped vs enveloped viruses?
Non-enveloped = Poliovirus Enveloped = Influenza + HIV
50
Most ___________ viruses are enveloped but very few _______________ viruses are enveloped
Mostly enveloped = animal viruses Mostly non-enveloped = plant/bacterial viruses
51
For enveloped viruses, how is the envelope acquired?
Obtained while "budding" out of the host cell as progeny make their exit
52
What does the viral envelope consist of?
1) Host cell membrane 2) Viral attachement proteins inserted into the membrane
53
Why is the viral envelope necessary for some viruses? (2)
1) Immune system evasion 2) Viral attachment and entry
54
How does the viral envelope contribute to viral attachment and entry into host cell?
Viral attachment proteins are often embedded within the viral envelope --> These proteins allow viruses to bind to the host cell receptors (attachment) + initiate entry
55
How does the viral envelope contribute to immune system evasion?
The viral envelope is derived from the host cell membrane and therefore has proteins that are made by the host cell and that the immune system recognizes as "self" --> Therefore, immune system doesn't recognize the virus right away since it "sees" it as "self"
56
What is a problem with the viral envelope?
It can typically get degraded in the external environment by desiccation and exposure to chemicals
57
What is the general 4-step process of viral replication?
1) Attachment 2) Entry 3) Replication and Production 4) Exit
58
What is viral attachment?
Binding of a virion to the host cell surface
59
For enveloped animal viruses, attachment typically occurs via what interaction?
An interaction between: 1) A host cell RECEPTOR 2) VIRAL ATTACHMENT PROTEIN
60
Viral Attachment Protein
Protein/s on the surface of a virus that aid in binding to a host cell
61
What are viral attachment proteins often referred to (based on their appearance)?
SPIKE
62
For NON-enveloped viruses, how does attachment typically occur?
Occurs usually in one of two ways: 1) Via viral attachment proteins on the vertices of an icosahedron 2) By the receptor interacting DIRECTLY with some AAs on the capsid
63
After a viral particle has attached to a host cell, what must occur?
ENTRY --> SOME component of the virion needs to get inside the cell
64
In viral entry, what components of the cell can enter?
1) Virion itself 2) Viral nucleocapsid 3) Viral genome
65
What are the 3 main methods of viral entry (for animal viruses)?
1) Endocytosis by ENVELOPED virus 2) Endocytosis by NON-enveloped virus 3) Membrane FUSION (by enveloped virus)
66
Endocytosis of Enveloped Virus: PROCESS (6 steps)
1) Virus attaches to cell by binding to the host cell receptor via its viral attachment proteins 2) Binding of virion triggers endocytosis to initiate 3) Endocytosis produces an ENDOSOME with the virion inside it 4) Acidification of endosome triggers conformational change in viral envelope proteins 5) Confromation change triggers FUSION of the endosome membrane with the viral envelope 6) Fusion = Nucleocapsid is released into the cytoplasm
67
What is an example of an enveloped virus that undergoes entry via endocytosis?
INFLUENZA
68
Endocytosis of NON-enveloped virus: PROCESS
1) Virus attaches to cell by binding to the host cell receptor (either via viral attachement protein or the capsid directly) 2) Binding triggers endocytosis to initiate 3) Endosome with virus is formed 4) Nucleocapsid **"escapes" endosome** 5) Nucleocapsid uncoats to release viral genome
69
What is an example of a non-enveloped virus that undergoes entry via endocytosis?
RHINOVIRUS
70
What is the difference between endocytosis entry between enveloped + NON-enveloped viruses?
**Enveloped** = Nucleocapsid released by membrane FUSION (between envelope and endosome) **Non-enveloped** = Nucleocapsid "escapes" endosome (NO FUSION STEP)
71
Via receptor-mediated endocytosis entry, what part/s of the virion enters the host cell?
THE ENTIRE VIRION (as it is engulfed within the endosome)
72
Membrane FUSION entry by **HIV**: Process
1) HIV attaches to host cell by binding to CD4 receptor 2) Bound virus interacts with CO-RECEPTOR 3) Conformational change is triggered in the embedded envelope proteins 4) The conformational change triggers FUSION of the envelope with the PM 5) Nucleocapsid is released into the cytoplasm!
73
How does HIV enter its host cell?
By FUSING with the plasma membrane! (NO ENDOCYTOSIS)
74
What is the primary host cell receptor HIV binds to?
CD4
75
For HIV entry, what part of the virus enters the host cell?
Just the NUCLEOCAPSID (Not the entire virion as a whole)
76
How do plant viruses enter their host cells?
Via distruptions in the cuticle covering plant tissue and holes in cell walls (usually areas of damage by insects, animals, etc.)
77
Do plant viruses recognize host cell receptors?
NO THEY DO NOT
78
How do viral progeny spread from cell to cell in plants?
Via PLASMODESMATA (cytoplasmic connections)
79
In bacteriophage entry, what actually ENTERS the host cell?
Just the bacteriophage GENOME
80
Process of bacteriophage attachment/entry:
1) Tail fibers of phage attach to receptors/binding sites on bacterial surface 2) Confromational change is triggered in the tail fibers 3) == Brings the BASE of the tail in contact with the surface of the host cell 4) Phage CORE PROTEINS penetrate the cell wall + tube extends down into the PM 5) Genome is "INJECTED" into the host cell
81
Assembly is a _________ and ____________ process
Assembly is a SEQUENTIAL and IRREVERSIBLE process
82
What does the following mean? "Assembly is a seqeuntial and irreversible process"
Means that assembly occurs in an ordered manner AND once a step in the order has been completed, it CANNOT be reversed!
83
What are the main methods of viral EXIT? (2)
1) Budding out of cell 2) LYSING cell

BIO 315 (25 decks)

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