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Immunology > Intro to Virology > Flashcards

Intro to Virology Flashcards

1
Q

Virus Characteristics

A
  • Obgligate Intracellular Parasites
    • Rely on metabolic machinery of host cells
  • Virion size and structure can vary rapidly - virions can be “naked” or “enveloped” with membrane
  • Genome can be either RNA or DNA
  • Intracellular phase - replication, transcription, synthesis of proteins and assembly of virions take place within infected cell
  • Extracellular phase - particles must pass from cell to cell, or throughout body, or between individuals
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2
Q

Viruses range in diameter from ___ nM to ___ nM

A

20; 300

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3
Q

The best way to see viruses is through:

A

Electron Microscopy

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4
Q

What does polythetic mean in relation to viruses

A

Any given virus group is described using a collection of individual properties - important for diagnosis, identification of new viruses, clarification of life cycle, drug design

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5
Q

Properties used for classification

A

Particle type

Tissue tropism (skin, respiratory tract)

Disease etiology

Serology (Cross-reacting epitopes)

Genome type (RNA vs DNA)

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6
Q

Virion structure: Capsids

A
  • Capsids can be made from one or few proteins that have repeating protein-protein contacts
  • Capsids can form naked viruses or be surrounded by a membrane for enveloped viruses
  • Capsid/envelope are the packaging, protection, and delivery vehicle during transmission
  • Exposed proteins on capsid and membrane are targets of neutralizing antibodies
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7
Q

Why is it important to distinguish Naked vs. Enveloped viruses

A

Major difference for virus structure, entry mechanism, environmental susceptibility…

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8
Q

Baltimore Classification

A

All viruses have to make RNA - classification scheme

  • Based on groups
    • Group 2 - single stranded DNA used to make double stranded DNA
    • Group 1 - double stranded DNA used to make +mRNA
    • Group 3 - double stranded RNA used to make +mRNA
    • Group 4 - +RNA(can be directly translated to protein) and -RNA used to make +mRNA (not efficient)
    • Group 5 - retrovirus (-RNA) to +mRNA
    • Group 6 - +RNA to single stranded (-)DNA to double stranded DNA
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9
Q

Are there more RNA viruses or DNA viruses?

A

RNA viruses

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10
Q

Define Terms

  • Virion:
  • Virus:
  • MOI:
  • CPE:
  • Viremia:
A
  • Virion: the viral particle
  • Virus: an infectious particle
  • MOI: multiplicity of infection
  • CPE: cytopathic effect
  • Viremia: spread of virus throughout the body via the bloodstream
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11
Q

Quantification of infectious virus

A
  • Plaque Assay - titration of the number of infectious progeny (unit = plaque forming unit, “pfu”)
  • Focus forming Assay - for viruses promoting cell growth rather than death
  • Single strep growth curve - provides quantitation of “burst size”
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12
Q

Tissue Culture models of infection:

A
  • Cytopathic effect
  • Cytolytic effect
  • Transforming
  • Induction/production/release of diagnostic enzymes
  • Expression of diagnostic antigens
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13
Q

What do virions contain

A

Naked Capsid virus = Nucleocapsid = DNA or RNA + structural proteins +/- enzymes and nucleic acid proteins

Enveloped virus = nucleocapsid + glycoproteins and membrane

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14
Q

Components of virion particle? (6)

A
  1. Genome, as a nucleoprotein complex
  2. Enzymes
  3. Auxiliary proteins that aid in disassembly after entry
  4. Structural proteins
  5. Attachment proteins
  6. Fusion proteins
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15
Q

Issues in understanding virus

A
  • Route of transmission
  • Cell/tissue tropism
  • Binding to and entering cells
  • Replication/ macromolecular synthesis
  • Morphogenesis (assembly)
  • Release from cells (egress) and host (transmission)
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16
Q

How is viral replication unique?

A

Viruses replicate by xeroxing - From one you get many new genomes

17
Q

Basic steps in viral life cycle (6)

A
  1. Attachment
  2. Penetration
  3. Uncoating
  4. Synthesis of components
  5. Assembly of viral components
  6. Exit/maturation
18
Q

Virion attachment

A
  • For both naked and enveloped viruses, a viral surface protein recognizes a receptor on the target cell
  • Binding of virus surface protein to cell surface receptor: protein or carbohydrate
  • Receptors may be ubiquitous or cell type specific
  • Virus recognition of its receptor is important for determining host range and cell tropism
19
Q

Virion entry

A
  • Naked viruses enter the cell via endocytosis and are surrounded by endosomal membrane
  • Some enveloped viruses use their glycoprotein to induce fusion of virus and cell membranes
  • Fusion releases capsid into the cytoplasm, leaving tracs of viral protein in the plasma membrane
  • Some enveloepd viruses are taken up by endocytosis, and fusion of their membrane with the membrane of an acidic endosomal compartment releases the capsid into the cytoplasm
20
Q

All viruses must synthesize _______ to make proteins

A

+mRNA

21
Q

The replication pathway a virus uses is reflected in, and depends upon, the ______ it encodes

A

enzymes

22
Q

Assembly/Morphogenesis - interplay between viral components and cell trafficking pathways

A
  • Proteins must be sorted to the correct nuclear or cytoplasmic location
  • Capsid proteins must assemble
  • The viral genome must be selectively encapsidated
  • Viral membrane proteins must be synthesiszed, modifies, and trafficked to the correct membrane
23
Q

Encapsidation into progeny virions

A

Once viral replication proteins are made, the viral genome is replicated - different viruses employ differen strategies and compartments for their replication - replicated genomes are assemblesd into progeny virions which are released from the cell

24
Q

Many naked viruses rely on ____ _____ for release

A

cell lysis

25
Q

Most enveloped viruses are released by ______ at the plasma membrane

A

budding

26
Q

Productive infection:

Latent infection:

Persistent infection:

Abortive infection:

A

Productive infection: Generally leads to cytopathic effect

Latent infection: No production of infectious virus particles, but genetic information of virus remains

Persistent infection: Chronic virus production

Abortive infection: Virus life cycle incomplete and virus lost

27
Q

Virus effects on host cell

A
  • Acute cytopathic effects
    • Membrane fusion of adjacent cells to form giant multi-nucleate cells called synctia
    • Shut off of host metabolism
    • Apoptosis
    • Necrosis
  • Cell transformation
  • No apparent effect
28
Q

What factors influence the species/organ/tissue/for disease? How are viruses spread between contacts?

A
  • Tropism
    • receptor
    • tissue specific
    • temperature or pH or activating proteases
  • Transmission
    • Respiratory
    • fecal/oral
    • direct contact
    • indirect contact
29
Q

Mechanisms of pathogenesis

A

Virus destruction of infected cels

Viral modification of infected cell function

Immune and inflammatory responses to virus infection

Combination of several factors

30
Q

Host Defenses

A

Innate response

Adaptive Response: humoral and cell mediated

Memory response

Immunology (17 decks)

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