viral lifecyle Flashcards
What are the 8 steps in a viral lifecycle
1)binding to cell surface proteins
2)entry
3)uncoating
4)replication
5)transcription
6)translation
7)vision assembly
8)release
What are the 7 steps of viral replication
1)adsorption (attachment)
2)entry
3)uncoating
4)genome replication and transcription
5)synthesis of virus components
6)assembly
7)release (and maturation)
What do viruses use as receptors
Components of cell membrane
What is adsorption(attachment) in viral replication
Random collision of virus to come into contact with receptor to attach to the cell for interaction between specific proteins on viral surface
What might some viruses use during adsorption (attachment)
May use more than one host cell receptor to gain entry into cell e.g HIV
What are neutralising antibodies
Specific for virion attachment proteins during adsorption to block interaction with receptors and prevent entry into cell
What is the influenza virus receptor
Sialic acid
What does the influenza virus recognise to enter a cell
Carbohydrate molecules present on glycoproteins
What are two glycoproteins on the surface of the influenza virus
Haemagluttinin and neuraminidase
What is a function of neuraminidase
Cuts the carbohydrate from the sialic acid to prevent the haemagluttinin from rebinding to sialic acid on surface of cell
What does again influenza HA (hemaggultinin) preferably bind to
SA (sialic acid) - a (alpha) - 2,3-gal-terminated saccharides
What does human influenza virus HA (hemagglutinin) prefer to bind to
SA (sialic acid) - a (alpha) - 2,6- Gal - terminated saccharides
What occurs during the entry process (penetration) during viral replication
Endocytosis
Fusion of virus envelope with cell membrane
What occurs during the uncoating process during viral replication
Release of viral genomes
Cell enzymes (lysosomes) strip off the virus protein coat
Virion no longer detected - “eclipse period”
How does HIV attach and enter into cells
surface unit (glycoprotein 120) protein attaches to CD4 receptors on target cell
What else does HIV require to attach and enter a cell other than CD4 receptors
Co-receptor required - chemokine receptors:
-7 transmembrane domains
-CXCR4 - T-cell
-CCR5 - macrophage
What is the mechanism of how influenza virus enters a cell
Hydrogen ions pumped into endosome lowering pH in endosome
Causes conformational change in HA (hemagglutinin)
Allows fusion of viral envelope with endosomal membrane
What is the process for SARS CoV in attachment and entry into a cell
S glycoprotein cleaved by TMPRSS2
Facilitates viral activation
Essential host factors for SARS-CoV-2 pathogenicity
TMPRSS2 is a potential target for antiviral drugs
How do non-enveloped viruses (poliovirus) enter and uncoat in target cell
Virus taken up into endosome
Conformational changes to viral structure proteins
Result in formation of a pore in endosomal membrane
Viral RNA is released into cytoplasm
Where does the process of assembly in viral replication occur
May take place in cell nucleus, cytoplasm or most enveloped viruses at plasma membrane
What is the process of release in viral replication
Sudden rupture of cell (non-enveloped virus)
Gradual extrusion (budding) of enveloped virus through cell membrane
May occur together with assembly
What is virus budding driven by
Virus protein interactions
What does the influenza virus require to become active when infected host cell when replicated
All 7 segmented RNA genomes
What is HIV maturation driven by
Virion protease
