Virus Classification and MUltiplication

Naming and Classification

Grouped by

• Nucleic Acid Type

• Strategy for Replication

• Morphology
  
  

Order → Names end in Virales → Nidovirales

Family → Names end in Viridae → Coronaviridae

Genus → Names end in Virus → Belacoronavirus

Common / Descriptive Name → Also Include Virus

Multiplication Cycle in Animal Viruses - 6 Phase

Adsorption → Attachment

• Virus Attaches to Receptor
  
  

Penetration → Virus Enter Cell

Uncoating → envelope + Capsid Digested, Nucleic Acid Released

Synthesis → Production of Components

Assembly (Maturation) → Assembly of Genomes, Proteins, Enzymes into Complete Progeny Virions

• If Virus has Envelope, it is not Complete until it Buds through the Cell Membrane

Release → Cell Lysis or Bud Off

Adsorption

Adsorb → To Attach

Virus finds Host and Adsorb to Receptor Site

Penetration and Uncoating

Animal Viruses

Endocytosis → Naked Viruses

Fusion → Enveloped Viruses

• Virus Envelope fuses with Host Cell Membrane and release Capsid into Cell

Once Inside Cell → Virus Uncoat

• Proteolytic Enzymes from Cell break down Capsid

Bacteriophage Injects its DNA into the Cell

• Lysozyme breaks down Bacterial Cell Wall

  • Capsid remains Outside

Synthesis

DNA viruses replicate in Nucleus

• DNA is Transcribed into mRNA

• mRNA is Translated into Viral Proteins

• DNA is replicated → More Genomes

RNA viruses replicate in Cytoplasm

• Some can be used directly as mRNA

• Some RNA needs to be copied into DNA by Reverse Transcriptase

Release of Mature Viruses

Enveloped Viruses → Exocytosis

Nucleocapsid Binds to Membrane → Pouch is Formed

Pinched off releases Virus with Envelope

Viruses are Shed Gradually without Destruction of Cell

DNA Viruses

Icosahedral → Enveloped or Not

• Enveloped → Double Stranded

  • Herpesviridae

  • Hepadnaviridae

• Non Enveloped → Single or Double Stranded

  • Single → Parvoviridae

  • Double → Papovaviridae or Adenoviridae

Complex → Enveloped → Double Stranded → Poxviridae

RNA Viruses

Icosahedral → Enveloped or Not

• Enveloped → Single Stranded

  • Togaviridae

  • Flaviviridae

  • Retroviridae

• Non Enveloped → Single or Double Stranded

  • Single → Picornaviridae or Caliciviridae

  • Double → Reoviridae

Helical → Enveloped → Single → A Shit Ton of Viridaes

Retroviridae

Carry Reverse Transcriptase

• Copies RNA into DS DNA

• Degrades OG RNA
  
  

Provirus

• Viral DNA in Host Chromosome

• Replicates along Host Cell DNA

• Latent or Expressed

Phages

Bacteriophage → Discovered in 1915

Parasitize every Bacterial Species

Sometimes makes Bacteria more Pathogenic for Humans

Lytic Phages

Lysogenic Phages

Lytic Phages

Infect Cell

Make more Inside → Burst Out

Lysogenic Phages

Temperate Phages

• Infect but no Kill

DNA into Host Chromosome and is now called Prophage

• Host Cell Phenotype Changes

Some Phages exist as Lysogenic Phase then become Lytic

Spontaneous Event, Chem, UV are capable of turning Prophages to Lytic

Inside Galactose Using Host → Gal Gene

Importance of Lysogeny

Cells are Immune to Reinfection with the same Phage

Phage Conversion

• Host Cell New Properties

• Prophage carries Genes to New Cells

  • Pathogens gets Toxins
    
    

Specialized Transduction

• Packages Bacterial DNA along with Voral in same Capsid

Lysogeny - The Silent Virus Infection

Temperate Phages

• Can Adsorb and Pent but do not Instantly Replicate or Release
  
  

Prophage → Inactive State where DNA is inserted into Host Chromo

Induction → Activate Prophage in Lysogenic Cell to Replicate and Lytic Cycle

Dangers of Lysogeny in Human Disease

Phage Genes in Bacteria Chromosome cause Toxins or Pathogens

• Lysogenic Conversion

  • Obtain new Traits

    • Responsible for Diphtheria, Cholera, and Botulism Toxin