Virus Proteins

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Virus Proteins

• Are coded by Viral Genes (and made only while a
  virus is infecting a cell) They
• Protect the viral nucleic acid
• Attach to receptors on the outside of cells
• Penetrate cell membranes
• Begin the program for virus replication
• Modify the infected cell ( making new virus
  particles)

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Viral Receptors

• Are coded by Host Genes (and are made regardless
  of whether a virus is present) They
• Often consist of membrane proteins
• But may also consist of carbohydrates attached to
  the outside of plasma membranes
• Do not exist for the sake of virus attachment but
  instead serve some function in host metabolism
• The Host Range of a virus often is determined by
  these molecules found on the outside of cells
• Host mutation to viral resistance can occur as a
  consequence of loss of specific viral receptors

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Virus Classification

• Viruses are classified
• According to their Genome Type
• Their Virion Morphology (as determined by
  electron microscopy)
• Their strategies of replication
• Their Serology (serotype), which is their
  reaction with specific antiserum
• (Increasingly) in terms of the sequence of their
  genomes
• International Committee of Taxonomy of Viruses
  (ICTV)

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Host Range vs. Tropism

• Another way that viruses can be classified is in
  terms of their host range
• Host Range is the range of species (strains, or
  varieties) of organisms that can serve as hosts
  for a given virus (also, narrow vs. wide)
• Similar to host range is a virus Tropism which
  is the range of tissue or cell types within a
  given host that a virus can infect

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Virus Replication
Steps of Virus Replication

• Adsorption (attachment)
• Penetration (nucleic-acid release)
• Synthesis (of RNA and proteins, as well as DNA if
  employed)
• Maturation (assembly of virion)
• Release (lysis or chronic release, e.g., budding,
  with the latter coinciding with release for
  various enveloped viruses)

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Enveloped Virus Replication
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Bacteriophage Lytic Cycle
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The Cultivation of Viruses
Animal Viruses
- Suitable Host Animal
- Embryonated eggs
- Tissue (Cell) Culture
Bacteriophages
- Plaque assay
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Embryonated Egg
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- Tissue (Cell) Culture
- Monolayers of animal cells
- Cell destruction can be localized if infected
cells are covered with a layer of agar the areas
of localized cell destruction are called plaques.
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