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Introduction to Viruses (Disease (Treatment of Animal Viral Infections (No…

- - - - no ribosomes or means of protein
      - nucleic acids molecules
        
        RNA
        
        single standed or double stranded
        
        linear or circular
        
        types
        
        positive-sense RNA
        
        the genome is ready for immediate translation
        
        negative-sense RNA
        
        genome must be converted before translation
        
        segmented
        
        genes exist on separate pieces of RNA
        
        Retroviruses
        
        carry their own enzymes to create DNA out of RNA
        
        DNA
        
        single stranded or double stranded
        
        linear ot circular
        
        Viruses carry only the genes needed to invade host cells and redirect their activity
        
        The number of viral genes is quite small compared with that of the cell
      - no ATP generating system
      - Matrix proteins
      - Enzymes
        
        not found in all viruses
        
        use host metabolic resources
        
        perform specific operations within the host cell
        
        polymerases that synthesize DNA and RNA
        
        replicases that copy RNA
        
        Proteases that cleave proteins
        
        reverse transcriptase that synthesizes DNA from RNA
        
        Integrase that inserts viral gene into host gene
    - - Capsid
        
        protein shell that surrounds the nucleic acid
        
        Composed of identical protein subunits called capsomeres
        
        capsomeres spontaneously self-assemble into the finished capsid
        
        Three different types of capsomeres
        
        Icosahedral
        
        human papillomavirus
        
        Complex
        
        Bacteriophage (virus that attack bacteria)
        
        have multiple types of proteins
        
        take shapes that are not symmetrical
        
        They are never enveloped.
        
        Helical
      - Envelop (not found in all viruses)
        
        external covering of a nucleocapsid
        
        usually containing a modified piece of the host’s cell membrane
        
        Spikes can be found on naked or enveloped viruses
        
        project from the nucleocapsid or the envelope
        
        Envelope allow viruses to dock with host cells at sites called receptors
        
        Enveloped viruses can bud from
        
        Host cell membrane
        
        Host nuclear envelope
        
        Host endoplasmic reticulum
        
        Viral envelope vs. host's membranes
        
        some envelope proteins attach to capsid proteins
        
        glycoproteins are exposed on the outside of the envelope
        
        some or all of the regular membrane proteins are replaced with viral proteins
      - Nucleocapsid
        
        the capsid together with the nucleic acid
        
        naked viruses consist only of a nucleocapsid
  - - - similarities in genetic makeup
      - chemical composition
      - structure
      - hosts and diseases they cause
- - - - entire virus is engulfed by the cell and enclosed in a vacuole or vesicle
    - - envelope merges directly with the cell membrane
      - nucleocapsid is released to the cell’s interior
  - - - Spikes
      - Specificity for infecting types of cells in one host
    - - envelope glycoproteins
    - - the limited range of cells that a virus can infect
    - - specificities of viruses for certain tissues
  - - - Some enter the host cell’s nucleus and are replicated and assembled there
      - The poxvirus is an exception
    - - Most RNA viruses replicate and assemble in the host cytoplasm
    - - turn their RNA genomes into DNA
  - - - Protein
      - RNA
    - - Packaging nucleic acid
      - Crystalline nature
    - - Empty procapsids are produced
      - Nucleic acid is inserted
      - Capsid proteins are synthesized by host cell ribosomes under the direction of viral late genes
  - - - Naked viruses are released by lysing the host cell
      - Mechanisms
        
        Virus-encoded proteins are incorporated into plasma membrane (some viruses use nuclear membrane, endoplasmic reticulum, Golgi apparatus, or other membranes)
        
        Nucleocapsid buds outward, forming the envelope during release
    - - health of the host cell
      - size of the virus
- - - - inclusion bodies
        
        compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm
      - syncytia
        
        fusion of multiple host cells into single large cells containing multiple nuclei
      - gross changes in shape and size or intracellular changes
  - - - herpes zoster virus (chickenpox and shingles)
      - HIV (AIDS virus)
      - herpes simplex virus (cold sores and genital herpes)
  - - - Papillomaviruses
      - Epstein-Barr virus
      - HTLV-1
  - - - every bacterial species is parasitized by various specific bacteriophages
      - often make the bacteria they infect more pathogenic
      - most contain double-stranded DNA
    - - Infect Escherichia coli
      - icosahedral capsid head
      - tail pins
      - central tube
      - fibers
      - collar
      - base plate
  - - - special DNA phages that undergo adsorption and penetration but are not replicated or released immediately
      - Instead the viral DNA enters an inactive prophage stage
    - - when a bacterium acquires a new trait from its temperate phage
  - - - Latency possible
      - ex. HIV
- - - - infects the human nervous system
      - causes gradual degeneration and death