Chapter 5 Flashcards
Virus Life Cycle Steps
Adsorption Entry (Penetration) Transcription Translation Genome Replication Assembly Exit
Adsorption
A virion attaches to host cell
highly specific molecular recognition
Receptor
cell surface molecule (usually protein) to which a virus specifically attaches
Antireceptor
Viral surface protein (or glycoproteins) that bear virus attachment site
Host range
the spectrum (type) of cells or organisms that a given virus can infect
Narrow host range
species-specific, or cell type specific
Broad host range
use a variety of receptors, may cross species, genus, family, or class, phylum or kingdom
ex. cross class, polio virus
Types of Interactions
Random collision
Non-covalent bonds
attachment initially reversible
Central Dichotomy
Outside cell, the virus must be stable
Inside cell, virus must be able to disassemble easily
3 Animal Virus Entry Methods
Endocytosis
Membrane Fusion
Endocytosis followed by membrane fusion
Endocytosis
“Bulk Transport” of material into eukaryotic cell by vesicles formed by invagination of plasma membrane
Endocytosis steps
Virion attaches to receptor Plasma membrane "Flows" around the virion More receptor binding membrane pinch off into cytoplasm Virion engulfed in an endosome Virion released into cytoplasm
Membrane Fusion
Between viral envelope and plasma membrane
used by enveloped viruses
Membrane Fusions Involve
Fusion Protein: Viral glycoprotein( dimer or trimer)
Fusion sequence
Conformational change
Intracellular transport in Eukaryotic Cell
Most RNA viruses replicate in cytoplasm
Most DNA in nucleus
Some are transported along microtubules to centrosome
They enter nucleus usually through nuclear pores
Uncoating
Remove capsid proteins to expose viral genome for accessing cellular machinery
Uncoating may occur
on cell surface
In cytoplasm
At nuclear pore
In nucleus
Bacteriophage attachment
Often involve tubes
receptors on appendages
antireceptors on tail or tail fiber
Bacteriophage penetration
Most phage inject DNA and leave capsid as ghost outside
viral lysozymes aid in this process
Plant Viruses
No receptor on plant cells
No Antireceptor on plant viruses
Penetration via break or lesion
Entire virion enters
