Biol 371 > Virology > Flashcards

Virology Flashcards

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1
Q

What is a virus?

A
  • An infectious agent
  • Can only replicate in a host
  • Non living form of life
  • They are extremely small
  • Tailored for a particular host
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2
Q

What are the 5 morphological groups of viruses

A
  1. Naked polyhedral virus ex. Mastadenovirus
  2. Naked helical virus
  3. Enveloped polyhedral virus ex. herpesvirus
  4. Enveloped helical virus ex. influenzavirus
  5. Complex coated virus ex. Mu bacteriophage
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3
Q

What are the 4 systems of taxonomy?

A
  1. Holmes classification (1948)
  2. LHT system (1968)
  3. ICTV (1990)
  4. Baltimore classification (1970)
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4
Q

What is the nature of the viral genome?

A

They are obligate intracellular parasites

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5
Q

Why study viruses?

A 
Has lead to many discoveries such as
- DNA carries inherited information
-enzymes involved in cellular DNA replication
- RNA splicing
Isolation of oncogenes
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6
Q

What are oncogenes?

A

a viral or cellular gene whose expression can leasd to cell transformation or tumorigenesis

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7
Q

What is the range of the smallest viruses and give an example

A

10-20 nm

ex Picornavirus

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8
Q

What is the range of the largest viruses and give an example

A

<1 micrometer

ex. Poxviridae (can be seen by phase contrast microscopy)

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9
Q

Why can viruses only replicate within a host?

A
  • lack ability to synthesize basic building block
  • can’t generate energy
  • don’t have enzymes for protein synthesis
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10
Q

What is the difference between a capsid and a nucleocapsid?

A

The nucleocapsid is a capsid with enclosed genome

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11
Q

What are the 7 viral groups within the Baltimore classification?

A

I. dsDNA - Poxviruses
II. ssDNA - Parvoviruses
III. dsRNA - Reoviruses
IV. +ssRNA - Togaviruses
V. -ssRNA - Orthomyxoviruses
VI. ssRNA-Reverse transcriptase with DNA intermediate - Retrovirus
VII. dsDNA-Reverse transcriptase - Hepadnaviruses

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12
Q

What are the components of the capsid?

A

Capsid -> capsomoere -> protomer

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13
Q

What happens to a helical capsid within an envelope?

A

The capsid is less rigid than if it were naked and may contain gaps exposing the nucleic acids

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14
Q

How are helical capsids formed?

A

When the nucleic acids bind to protomers within a disk creating a locked washer then more disks can stack,

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15
Q

What describes helical capsids?

A
  • number of sub units per turn

- displacement along the helical axis between one sub unit and the next

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16
Q

What is the problem with polyhedral capsids and how do they over come this?

A

problem: protomers are asymmetric, so multiple protein-protein interactions of both sides
solution: arrange protomers in triangular configurations

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17
Q

What is quasi-equivalence?

A

One subunit has different interactions with other subunits to allow for a more complex capsid

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18
Q

What does the triangulation number (T) tell us?

A

That there are T multiples of 60

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19
Q

Describe the genome and capsid of Parvoviridae.

A
  • ssDNA

- T=1

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20
Q

Describe the genome and capsid of caliciviridae.

A
  • ssDNA

- T=3

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21
Q

Describe the genome and capsid of Caulimovirus

A

-dsDNA

T=7

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22
Q

Describe the genome and capsid of Hepadnavirus

A

-dsDNA

T=4

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23
Q

What are envelopes composed of?

A
  • lipid bilayer from host

- viral glycoproteins

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24
Q

What are matrix proteins?

A

They are proteins that interact with the capsid and the envelope

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25
What can the viral envelope be derived from?
- plasma membrane - Golgi apparatus - nuclear membrane
26
Why don't plant viruses usually have envelope?
The envelope would cause difficulties in viral penetration and viral release
27
What does MOI stand for?
Multiplicity of infection
28
What does MOI mean?
the number of infectious virus particles per cell
29
In general what are the 7 steps of virus replication?
1. Binding to cell receptor 2. Entry into cell and uncoating 3. Early gene expression ->those for replication of genome 4. Replication of viral genome 5. Late gene expression ->those of making structural proteins 6. Assembly of virions 7. Exit
30
What is the eclipse period?
When all virions are within the cells but are not far enough along to assemble and release new virions
31
What is the burst time?
The time from phage adsorption in host cell to release from the host
32
What is the burst size?
The number of newly synthesized phage produced from one infected cell
33
What are the 2 lifestyles phage exhibit?
1. Lytic phase | 2. Lysogenic phase
34
What happens during the lysogenic phase?
- phage genome recombines with bacterial chromosome | - virion assembly is delayed until expression or vial proteins in the host genome (ie daughter cell carries the virus)
35
In the lysongenic phase how do they overcome cell lysis?
Vial genes that are expressed prevent the lysis gene from being expressed. Once the viral proteins are broken down when the cell is in stress the lysis gene is expressed killing the cell.
36
How does the togavirus enter the cell?
Togavirus does not have an envelope but has spikes on its surface that bind to host cell receptors.
37
How does the herpesvirus enter the cell?
Herpesvirus is an enveloped virus that uses glycoprotein spikes that bind host receptors. The envelope and plasma membrane fuse releasing the capsid into the cytoplasm
38
In general how does uncoating occur?
Capsid proteins are degraded by host protease enzymes
39
What are the 4 viral uncoating strategies?
1. Pore formation (picornavirus) 2. Plasma membrane fusion (Paramyxoviridae) 3. Endosomal fusion (influenza) 4. Endosomal lysis (adenovirus)
40
What 2 types of proteins are required on viruses who use the plasma membrane fusion method?
1. Host receptors | 2. Fusion proteins
41
How does a virus cause fusion within an endosome?
By decreasing the pH it stimulates viral fusion proteins releasing the genome
42
How does endosomal fusion and lysis differ?
The only difference is that the endosome is lysed
43
Do dsDNA viruses have their own replication system?
No, they use the host cell enzymes
44
Which classes use RNA dependent RNA polymerase?
Class III, IV and V | -replicates viral RNA using ss or ds RNA as the template
45
What does RNA dependent RNA polymerase do?
Replicates ss or ds RNA as a template
46
What are the difficulties detecting viruses?
virus analysis requires purification | virus purification requires analysis
47
Describe the differences between direct and indirect methods.
Direct counting required that all viruses are counted including those who may not be infectious.
48
Why does one virus particle not equal one infectious virus?
- might not be intact - may have defective genomes - empty capsid
49
What are the 4 ways of direct counting using a TEM?
1. Immune TEM 2. classical immune TEM 3. Solid phase immune TEM 4. Immune gold labelling TEM
50
What are the 4 methods of indirect counting?
1. Plaque assay 2. Cytopathic effects 3. End point assays 4. Nucleic acid detection
51
How do you calculate PFU?
PFU=number of plaques/(dilution factor x virus volume)
52
What is necrosis?
cell lysis in plants
53
What is cytocide?
host cell lysis and death
54
What method is used to define the number of virions in a vaccine?
End point assays
55
What is hemagglutinain used for?
Can easily detect viruses as it caused the RBC to spread out
56
Why is the MOI usually greater than 1?
because the ratio of virus particles to infectious particles is greater than one
57
How do viruses without an envelope enter the cell?
They enter through endocytosis and then either lyse the endosome (Adenovirus) or create a pore (Picornavirus)
58
What are the 2 ways enveloped viruses enter the cell?
1. Fusion and fission of the viral envelope with plasma membrane 2. Receptor-mediated endocytosis followed by fusion with the endosome
59
What are syncytia?
They are the formation of multinucleated cells
60
What do non-enveloped viruses use for binding sites?
Either protrusions or cavities
61
What do clathrin-coated pits, caveolae and lipid rafts all have in common?
Enter through and early endosome
62
What is macropinocytosis?
Receptors signal for the plasma membrane to ruffle allowing internalization of fluid into large vacuoles called maropinosomes
63
Which direction does the kinesin move?
To the + end away from nucleus (where the actin is being added)
64
Which direction does the myosin move?
To the - end Towards the MTOC and closer to the nucleus
65
What level of biosafety do they use for the ebola virus?
BSL4 - wear suits
66
Describe the morphology and genome of the ebola virus.
- enveloped - helical - (-)ssRNA
67
Where does ebola prefer to replicate?
monocytes/macrophages and dendritic cells
68
What are the secondary sites of the ebola virus?
hepatocytes, endothelial and epithelial cells
69
What are the two types of vaccines?
Passive and active
70
What are the two types of active vaccines?
Modified live vaccines which contain attenuated organism. | Inactivated vaccines
71
What are the advantages and disadvantages of the modified vaccine?
``` Advantages: Only require single dose for lifelong immunity. Strong immune response. Local and systemic immunity. Disadvantages: Potential to revert to virulence. Not recommended for people who are immunosuppressed. Poor stability. Potential for contamination. ```
72
What are the advantages and disadvantages of the inactivated vaccines?
``` Advantages: Stable. unable to cause infection. constituents clearly defined. Disadvantages: Need several doses. Local reactions common. Shorter lasting immunity. ```
73
What is a vectorized attenuated vaccine?
They take genes from a virus for its receptors and insert into a none toxic virus allowing the body to generate antibodies to the infectious virus.
Biol 371
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