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Micro and Immuno - Exam 2 > Virus Classification, Structure, and Replicaiton > Flashcards

Virus Classification, Structure, and Replicaiton Flashcards

1
Q

What’s the difference between a Virus and a Bacterium

A

Bacterium can replicate on their own.

Viruses need a host to replicate

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2
Q

What’s the difference between a Virus and a Toxin

A

A virus can replicate given a host.

A toxin is created by a cell.

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3
Q

What are the theories of Virus Origins

A

Cellular Origin

Autopoetic Origin

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4
Q

Autopoetic Origin Theory

A

Proposes that viruses were once autopoetic entities, but became dependent on cells for replication

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5
Q

Cellular Origin Theory

A

Proposes that viruses were once cellular components but over time evolved seperately

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6
Q

Virus Particle Structure can be organized by…

A

Composition
Shape
Size

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7
Q

What is a nucleocapsid?

A

An RNA or DNA in a core that is protected by a protein coat (capsid)

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8
Q

What is a capsid comprised of?

A

Repeating protein subunitys called capsomeres

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9
Q

What are envelopes?

A

Virus-modified cellular membranes that are acquired upon exit from host cells

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10
Q

What happens to enveloped viruses when exposed to lipid solvents in a lab?

A

They are rendered noninfectious

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11
Q

How big is a “small virus”

A

18 nm

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12
Q

How big is a “large virus”

A

300 nm

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13
Q

What is an advantage of a small virus?

A

Small viruses replicate faster

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14
Q

What is an advantage of a large virus?

A

Large viruses carry more immune modulating genes that can allow for more replication and shut down the immune system

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15
Q

What are the different virus genome compositions/classifications

A

DNA - double stranded
DNA - single stranded
RNA - double stranded
RNA - single stranded +, -, or ambisense

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16
Q

What is special about ambisense ssRNA

A

Resembles -ssRNA but it can read +ssRNA or -ssRNA

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17
Q

What are the different structures of virus genome?

A

Linear
Circular
Segmented
Diploid

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18
Q

ssDNA replication

A

Needs a double stranded structure to bind to - uses a hairpin structure. Relies on host cell replication machinery

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19
Q

dsDNA replication

A

Similar to double stranded DNA replication in humans

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20
Q

+ssRNA replication

A

Uses host ribosomes

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21
Q

-ssRNA replication

A

needs RNA dependent RNA polymerase to make + strand, which can serve as a template

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22
Q

What are the steps of virus replication

A 
Attachment
Entry
Transcription
Translation
Replication
Assembly
Release
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23
Q

Virus attachment

A

Virus receptor bind to cellular receptors. They usually don’t mimic normal ligands, and bing somewhere other than the normal binding zone. Still triggers the cascade to cause virus to enter.

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24
Q

Viral receptors

A

Usually don’t mimic cell receptor’s normal ligands.
Typically are spike-like projections on viral particle surface.
May require a co-receptor

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25
Q

What can genetic engineering do to viral attachment?

A

It can change receptor recognition.

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26
Q

What is a major determinate of virus tropism/host range?

A

Attachment

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27
Q

What is a major factor for eradication of a virus?

A

Host range

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28
Q

(T/F) A virus can infect a human and a fungus.

A

False - a virus range won’t cross kingdoms

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29
Q

(T/F) A virus can infect all life forms

A

True

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30
Q

What are the pathways of virus entry into a cell?

A

Receptor mediated endocytosis

Direct penetration of plasma membrane

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31
Q

Non-enveloped virus cell entry

A

Not well understood.

Enters either through pores or membrane disruption

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32
Q

Enveloped virus cell entry

A

Enters through membrane fusion
HA proteins aid in attachment of the virus, lowering pH, which causes a conformational change and the membranes fuse
(Receptor induced)

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33
Q

After entry, what occurs to viruses that undergo nuclear replication?

A

The genome and remaining protein coat (nucleocapsid) are transported to the nuclear membrane, and the genome gets delivered to the nuclesus

34
Q

After entry, what occurs to viruses that undergo cytoplasmic replication?

A

The genome is released into the cytoplasm, and the genome gets transported to the intracellular site of replication. Many RNA viruses replicate in membrane associated complexes.

35
Q

What is important about dsRNA viruses upon entry?

A

It is important that they NEVER release their genome from the entering particle, because this would trigger an immune reponse.

36
Q

+ssRNA virus Transcription

A

+ssRNA serves as mRNA - and production of new transcripts can occur later using a -ssRNA template

37
Q

-ssRNA and dsRNA transcription

A

These viruses must bring their own polymerases into the cell

38
Q

DNA virus transcription

A

These viruses rely on cellular RNA polymerase

39
Q

Virus Translation

A

All viruses require the cell’s ribosomes to produce proteins.

40
Q

Viral proteins production can be regulated at what levels?

A

Both the transcription and translation levels

41
Q

+ssRNA genome replication

A

Genome serves as a template for translation.

Polymerase makes -ssRNA copy as a template for the new genome

42
Q

-ssRNA genome replication

A

Virus particle musct include the viral polymerase
Polymerase makes a messenger for translation
The genome replicated through a +ssRNA intermediate

43
Q

dsRNA genome replication

A

Virus particle includes viral polymerase
dsRNA induces innate immune response, so the genome stays inside the particle
mRNA is synthesized in the particle and is exported to the cytoplasm
mRNA serves as the + strand and the - strand is synthesized during assembly

44
Q

ssDNA and dsDNA genome replication

A

Must gain access to the nucleus, prepare the cell for DNA replication, and ensure the genome ends are copied

45
Q

Virus assembly

A

Package new genomes into functional particles

Structural proteins are localized to aid in assembly (cellular viral “factories”)

46
Q

What are the virus assembly mechanisms?

A

Adenovirus
Reovirus
Retrovirus

47
Q

Adenovirus assembly

A

Empty protein coats import a newly replicated genome

48
Q

Reovirus assembly

A

RNA is packaged during capsid assembly

49
Q

Retrovirus assembly

A

Preassembly on a membrane

50
Q

What are the different types of virus release?

A

Lysis
Weak Lysis
Budding

51
Q

Lysis release

A

Best known for bacteriophage

Viral molecule that rupture cellular membrane

52
Q

Weak Lysis release

A

Depends on membrane breakdown after cell death

53
Q

Budding release

A

Enveloped viruses use cell membranes as the outer coat of the virus particle

54
Q

What advantages/disadvantages come with targeting virus replication in the nucleus.

A

It has to go through 2 membranes - the nucleus and the cell

55
Q

How does understanding a virus’ replication process help to design antivirals?

A

Antivirals can be made to target the RNA –> DNA step

56
Q

What advantages/disadvantages come with lytic versus non-lytic infection?

A

Lytic infection is quicker for progeny to get to other cells, but a higher chance of triggering an immune response

57
Q

Explain the one-step growth curve of viral kinetics

A

Infects every cell at the same time

All cells die at the end of infection

58
Q

What are the phases of viral kinetics?

A

Eclipse
Exponential growth
Plateau

59
Q

Eclipse

A

Attachment and uptake of virus

60
Q

Exponential growth

A

Replication and Assembly of virus

61
Q

Plateau

A

Cell death

62
Q

Initial discovery of viruses

A

Done by either by disease in a host or contaminant in a cell culture

63
Q

Confirmation of viruses

A

Purification of a virus

Confirmation of disease (by animals, eggs, or cell culture) - cell culture is prefered

64
Q

What are the Principle of Detection and Quantification Methods

A

Infectivity
Physical
Genome
Serological

65
Q

Molecular methods are useful for detecting…

A

Viruses that cannot be cultivated

66
Q

Cytopathic Effect

A

Cell Rounding
Syncytia Formation
Inclusion bodies

67
Q

Fluorescent Focus Assay

A

Infect cells
Expose the virus antigen
Stain them with labeled antibody
Count areas that flouresce

68
Q

Plaque assay

A

Take a cell monolayer
Inoculate it with dilute virus
Infected cells die which leave a clear area (plaque)

69
Q

Infectious dose

A

ID50, IU50, TCID50
Systems: tissue culture, eggs, animals
Inoculate these systems with different dilutions of virus
Calculate the concentration based on the number infected

70
Q

What are the different Infection Assays?

A

Cytopathic Effect
Fluorescent Focus Assay
Plaque assay
Infetious dose

71
Q

What are the different Particle Assays?

A

Electron microscopy

Hemagglutin assay

72
Q

Electron microscopy

A

Direct image of virus particles

Calibrate with latex bead standard

73
Q

Hemagglutin assay

A

Used with viruses that bind to RBCs
Mix constant number o RBCs with different dilutions of virus
If a virus concentration is sufficient, a matrix of RBCs and virus is formed
Matrix does not allow RBCs to pellet

74
Q

What are the different genome assays

A

Polymerase chain reaction (PCR)

Southern (DNA) and Northern (RNA) blots

75
Q

Polymerase chain reaction

A

Use a DNA primer to a specific virus
Amplify the gene
Very sensitive

76
Q

Southern and Northern blots

A

Isolate DNA or RNA
Separate by electrophoresis
Use labeled DNA probe to detect

77
Q

What are the different serological assays

A

Virus neutralizaiton
Enzyme Link Immunoabsorbant Assay (ELISA)
Western (Protein) Blot

78
Q

Virus neutralization

A

Antibody binding to virus can block infection

Virus concentration determined by amount of antibody needed

79
Q

Enzyme Link Immunoabsorbant Assay

A

Antibody recognition of virus

Amplification by enzyme linked to antibody

80
Q

Western (Protein) Blot

A

Separate proteins by electrophoresis

Probe proteins using an antibody

Micro and Immuno - Exam 2 (11 decks)

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