T1iii: Outline the classification of viruses

Virus – an infectious organism composed of a molecule of DNA/RNA shielded in a protein coat that is only able to multiply within the living cells of a host.

Classification

1. Type & Structure of Nucleic Acid

    • DNA/RNA
    • Single strand/Double strand
      • SS RNA
        • Polarity+ (can be used as template for protein synthesis)
        • Polarity- (cannot be used as a template for protein synth)

2. How it Replicates

  • Small DNA = use host to replicate genome
  • Large DNA = provide all their own enzymes and molecules for replication
  • DNA = assemble in nucleus
  • RNA = assemble in cytoplasm

3. Capsid Shape

    • Helical
      • Repeated single polypeptide unit
      • Nucleic acid surrounded by capsid
    • Icosahedral
      • Several different polypeptides
      • Assembled together
      • Nucleic acid genome located in empty space surrounded by Icosahedral structure

4. +/- Envelope

  • Lipid membrane = envelope
  • Derived from host cell memb
  • No envelope = naked virus