1. Characteristics
   1. Genetic Material: Either DNA or RNA
   2. Can't replicate without a host cell
   3. Can't divide by binary fission, Mitosis or Meiosis
   4. Can't make energy (get it from Host cell)
   5. Can't make their own Protein or Genetic material (steal it from host cell)
   6. Intracellular Parasites
   7. Size range from 10-300 nm
   8. Can infect all Organisms
   9. Genetic Material surrounded by Capsid or Protein coat (Small protein units called Capsomeres)
   10. Some have an outer envelope
   11. May also have tail, sheath and tail fibres
2. Classification
   1. Type of genetic Material
   2. shape and/or size of Caspid
   3. Number of Capsomeres
   4. Presence or absence of an envelope
   5. Type of hosts it infects
   6. Type of disease it produces
   7. Target cell
   8. Immunologic or antigenic properties
3. Host Range
   1. Is the spectrum of host cells the virus can infect
   2. Mostly single host range
      1. Invertebrates
      2. Vertebrates
      3. Plants
      4. Protists
      5. Bacteria
      6. Fungi
   3. Rarely cross the hist range Barrier
   4. Determined by
      1. Attachment sites on the host
      2. Availability in the potential host the factor for viral replication
4. Origin
   1. 3 Major theories
      1. Viruses are remnants of past infections
      2. Cells came before viruses
         1. Viruses are degenerate cells or cell fragments
      3. Viruses represent a separate evolutionary branch
5. Attachment sites
   1. Outer surface of virus interact with specific receptor sites on surface of potential host cell
   2. Complementary component held together by hydrogen bonds
6. Antiviral agents
   1. Interfere with the Phases of viral multiplication
   2. May disrupt an enzyme or protein
   3. May interfere with the synthesis of viral parts like DNA, RNA or Protein synthesis
7. Some Viruses
   1. Retroirus
      1. Genetic information is single stranded RNA
      2. Have a special enzyme called Reverse Transcriptase
         1. Makes DNA from RNA
      3. Integrate their newly formed double stranded DNA into the host cell
      4. Many Retroviruses are responsible for junk DNA in our genome
   2. Plant Virus
   3. Bacteriophage
      1. Viruse that infects Bacteria
      2. Types
         1. Virulent Bacteriophage
            1. Causes lytic cycle
            2. Steps
            3. Attachment
            4. Penerration
            5. Biosynthesis
            6. Assembly
            7. Release
         2. Temperate Bacteriophage
            1. Do not immedietly begin lytic cycle
            2. DNA remains embedded in Bacterial cell Chromosome
   4. Animal Viruses
      1. Attach to Specific binding sites on cells
      2. This affects what species and which cell type is infected
      3. Multiplication of Animal Viruses
         1. Attachment
         2. Penetration
         3. Uncoating
         4. Biosynthesis
         5. Assembly
         6. Release
   5. Oncogenic Viruses
      1. Viruses that cause cancer
8. Taxonomy
   1. Based on guideline by ICTV (International Committee on Taxonomy of Viruses)
   2. Grouping based on
      1. Nucleic acid type
      2. Strategy of replication
      3. Mosphology
   3. Names
      1. Older names: end with - ales
      2. Family Name: end with- Viridae
      3. Genus Name: End with - Virus
      4. Species name: Described by common name
      5. Subspecies name:Designated by number