Virus Life Cycle Flashcards
In order to grow, need…
Tropism: right host
Susceptible: cells with right receptors
Permissive: appropriate intracellular environment
Biosynthesis machinery
Abundant building blocks (NT, AA, ATP, lipids, etc)
Time to finish replication
Viewing viruses
Not visible by light microscopy, use inverted microscopes
Infections may cause cytopathic effects (holes in cells)
Virus replication
Recognition Attachment Entry Uncoating Transcription of mRNA Protein synthesis Replication of genome using host cell nucleotides Assembly of virions Egress
Recognition
Interactions between virions and tissues
Attachment
Binding of virion surface molecule to receptor on preferred tissue cell type
Entry
Multiple routes that vary by cell type
Penetration: engulfment of entire Virion into cell (receptor-mediated endocytosis, pinocytosis, phagocytosis)
Fusion: Virion envelope fuses with plasma membrane leaving parts behind
Uncoating
Release of genome into cell by capsids
“Eclipse phase”
Can be at plasma membrane, within endosomes or at nuclear pore
Transcription of mRNA
All viruses must make mRNA from viral genomes
Regulated by viral and host transcription factors
RNA viruses need RNA-dependent RNA polymerase (RDRP) to transcribe
Protein synthesis
Viral mRNA translated by host machinery always
Viral proteins sort to site of virion assembly
Replication of genome
Use host cell nucleotides
Viral RNA-dependent RNA polymerase, viral DNA polymerase, host cell DNA polymerase, host cell RNA polymerase II
Assembly of virions
End of eclipse phase
Capsid forms shell, viral DNA inserted, enveloped with membrane from ER, Golgi or plasma membrane
Egress
Virions released by budding, exocytosis, lysis, cell to cell spread (jump from one to next while lysing), fusion (syncytium)
