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
What state does HIV need to be in to be infections
Only mature HIV is infectious
What does DNA dependent DNA polymerase make
Makes DNA from DNA
What does DNA dependant RNA polymerase make
Makes RNA from DNA
What does RNA dependant RNA polymerase make
Makes RNA from RNA
What does RNA dependant DNA polymerase make (reverse transcriptase)
Makes DNA from RNA
What do all RNA viruses encode
An RNA dependant RNA polymerase
What are characteristics of +ive strand RNA viruses
Genomic RNA acts as mRNA on cell entry
Translated to produce the polymerase
What are characteristics of -ive strand RNA viruses
Need to carry polymerase in the virion
Required to convert -ive RNA to +ive mRNA after entry
What type of transcription does HIV undergo
Transcripts (alternative splicing)
How do anti-viral drugs work and what it uses
Attachment antagonists
Inhibit uncoating
Inhibit DNA/RNA synthesis
Block maturation
How does the drug amantadine work with influenza drug targets
Block the ability to lower the pH within endosome and block aspects of uncoating process
What are neuraminidase inhibitors and what do they do
Drug to treat influenza and block the virus being able to released from an infected cell
