Viruses #1

Viruses #1

1. General Features

   • Characteristic common with living oragnisms
     • Reproduce at a high rate, only inside living host cells
     • Their genome is suscptible to mutation
   • Characteristics common with non-living organisms
     • Acellular organisms
       • No cytoplasm or cellular organisms
     • Cannot grow and divide independantly
     • Replication occurs using the host cell's metabolic machinery
     • Posses either DNA or RNA, not both
       • Makes up the core
   • Protein Capsid
     • Made up of small repeated proteins
     • Directs attachment to host cell
     • Provides protection
   • Shape
     • Helical
       • Similar to RNA genome acting as a structure that binding proteins condense onto
     • Icosahedral
       • Generally, 3 porteins form a triangular face
       • 20 triangular faces
   • External Features
     • Matrix Proteins
     • The Viral Envelope
       • Formed from host membrane
         • Derived from Host cell budding
           • Matrix proteins glue the capsid to the membrane
             • Glycoproteins are anchored into the membrane
               • Essential for recognition attachment
   • Complex Virus Structures
     • Comprise an icosahedral head, a tail and tail fibers
     • T-Phage
       • Six small spikes at the base of the contractile tail are used to attach to the host cell
         • Inject viral DNA into cell

2. Viral Genome and Classification

   • Holmes
     • Split into 3 groups
       • Attacks Bacteria
       • Attacks Plants
       • Attacks Animals
   • Classical
     • Based on 3 principles
       • Classifying the virus not the host
       • Nucleic acid genome
       • Shared physical properties of the infectious agent
     • Uses Order, Family, Subfamily, Genus and Species
   • Baltimore
     • Based on genetic contents and replication strategies of viruses
     • 7 Classes
       • dsDNA
         • Double Stranded
       • ssDNA
         • Single Stranded
       • dsRNA
       • (+)sense ssRNA
       • (-)sense ss RNA
       • RNA reverse transcribing
       • DNA reverse transcribing
   • Genomic - Ongoing system
     • Ordering of viruses within and between families based on DNA/RNA sequencing

3. Viral Life Cycle

   • General
     • Attachment to cell
       • Penetration of viral DNA/RNA
         • Transcription and/or Translation
           • Replication of new viral proteins
             • Assembly of new viruses
               • Release the new viruses
   • Animal Viruses
     • Replication
       • 4 Possible outcomes
         • Lytic Growth
           • Grows and normally kills the infected cell
             • Releases multiple viruses
         • Lytic Growth with latency
           • Grows and stays dormant until immunity is lowered
         • Slow Growth
           • Slow development over many years, slowly releasing viruses
         • Cancer
           • Tumor formation and multiplcation
     • 1 Attachment (specific host cell)
       • Penetration via Endocytosis
       • Fusion of enevelope
         • Envelope fuses with membrane and release capsid inside the cell
     • Coping
       • Most animal cells are not replicating
         • Induces replication
         • Carry the genetic information for replication
         • Grow only in replicating cells
         • Become an RNA Virus
           • BUT
             • DNA Viruses can use host machinery to replcation
             • DNA viruses can also use repair mechanims from the host cell