Viral Structure

Viral Structure

1. Virion

   • Mature, released virus that can infect host cell

2. Genome

   • DNA
     • Single or double stranded
     • Linear or helical
   • RNA
     • + sense
     • - sense
     • ambisense

3. Outer protection

   • capsid
     • icosahedral
       • polyhedron w/ 20 faces
     • rigid structure
     • resists drying, acid, detergent
   • Enveloped
     • icosahedral capsid or helical ribonucleocapsid beneath envelope
     • outer layer membrane
       • lipids, proteins, glycoproteins
     • disrupted by drying, acids, detergents, solvents

4. Viral Attachment

   • depends on capsid structure and glycoproteins in envelope
   • Tropism
     • affinity for specific tissue type
   • attachment is very specific
     • specific host cell receptors
   • Viral Attachment Proteins
   • naked capsid viruses
     • small viruses: structural composition to adhere to specific host cell receptors
     • large virus: structural composition and fiber-like proteins extending out of capsid to adhere
   • enveloped virus
     • glycoproteins extend out from vision
       • VAPs
         • specificity
   • Viral Penetration
     • naked capsid
       • receptor-mediated endocytosis
       • Viropexis
         • Direct penetration of genome through host cell membrane via interaction between capsid and membrane
           • picornaviruses
           • papovaviruses
     • enveloped viruses
       • viral membrane fusion with host cell membrane
     • Viral uncoating
       • DNA
         • carried to nucleus
           • Not poxviruses
       • RNA
         • stays in cytoplasm
           • Not orthomyxoviruses or retroviruses
       • poxvirus
         • encode own mRNA w/ vision-contained enzymes
       • Retroviruses
         • own polymerases for RNA synthesis
       • RNA viruses
         • encode own enzymes for transcription and replication
           • host cell can't replicate viral RNA