Viral replication Flashcards
what are the 3 main stages/phases?
eclipse phase,maturation and release phase, decay of viral progeny stage
what is the range of time viral replication can take?
large virus= 70hr bacteriophage=30mins
what is the eclipse phase?
time between infection and appearance of maturity in the cell (period virus is being uncoated)
what are the main steps in viral replication? (5)
1) enters cell
2) uncoating of DNA
3) replication for new DNA and protein synthesis for coat protein
4) assembly of progeny virus particles
5) exit from cell
what determines which cells can be infected?
different viruses recognize different cellular receptors (only small 5 of cells are targeted)
what is tissue trophism?
the cells and tissues that support growth of a bacteria or a virus (caused by tissues on cell surface that virus can recognize and bind to)
true or false: the type of receptor the virus can bind to is always related to the viral infection type?
False. Although some receptors are in places that seem relevent to the virus (e.g Influenza has respiratory tract receptors and polio has receptors in alimentary canal) the type of receptor a virus can recognise can also be down to chance.
what are the influenza receptors?
respiratory tract
where are the polio receptors?
alimentary canal
what two main mechanisms are used in host cell infection and disassembly?
fusion or endocytosis
what does HIV-1 retrovirus show wrt target cells?
cellular trophism that allows switching between target cells through mutation
what can HIV-1 infect? (2)
Macrophages and T-cells
what is a macrophage?
a large phagocytic cell found in stationary form in the tissues or as a mobile white blood cell
what are t-cells?
a lymphocyte of a type produced or processed by the thymus gland and actively participating in the immune response
where do most DNA viruses replicate? where do most RNA viruses replicate? exceptions:
most DNA viruses replicate in
the nucleus (except poxviruses)
most RNA viruses replicate in
the cytoplasm (except retroviruses)
outline RNA virus replication for ssRNA +
for + genome is mRNA so translation is direct –> can be translated directly to form capsid and RNA dependent DNAP which aids RNA synthesis –> assembly follows.
outline RNA virus replication for ssRNA -
Rna dependent RNApolymerase must be carried to synthesis mRNA then translation,protein production and more DNAP follows –> assembly
describe HIV host cell infection process. Fusion or endocytosis?
FUSION. virus binds to receptors on cell surface,triggering conformational changhe,leads to FUSION of cell membrane,capsid enters host cell,lipid protein left behind,uncoating follows.
MEMBRANE PROTEIN LEFT ON SURFACE OF HOST CELL
describe Influenza host cell infection process.Fusion or endocytosis?
ENDOCYTOSIS. virus binds to cell surface,surface binding receptor causes endocytosis, endosome in,endosome acidifies causing fusion and uncoating.
MEMBRANE PROTEIN BROUGHT INTO HOST CELL
what do HIV and influenza have in common wrt their structure?
the both have membranes with proteins on
describe polio host cell infection?
No membrane with protein, capsid binds directly to host cell,DOES NOT FUSE, virus is drawn in,conformational change,RNA genome enters through a pore
describe adenovirus infection process?
ENDOCYTOSIS. here capsid isn’t just for protection but the proteins bind directly to cellular receptors which triggers conformational change.Needs to get to nucleus through a pore
what type of virus is an Adenovirus?
DNA virus
what do sense - viruses have to have to make +RNA first?
polymerase in the viron particle
what does RF stand for?
replicative form
What happens in dsDNA virus replication?
virus in cytoplasm is transported to nucleus;transcription,translation,replication and assembly in nucleus
what do dsDNA virus’ use from the host?
uses host polymerases and ribosomes (many host transcription factors bind to ViralRNA increasing and controlling expression)
what are often cleaved by host proteases?
viral polypeptides
what must retroviruses contain?
reverse transcriptase to make DNA from RNA and replicate in the nucleus
what is an integration even wrt retroviruses?
when dsDNA becomes integrated to host genome
Does the host affect a virus’ life cycle?
yes the host provides polymerases etc so latency and persistence is definitely affected by the host
what does gag encode for?
capsid protein and structural core
what does env encode?
envelope protein
wha tdoes pol encode for?
replication proteins
what are gag,env,pol all part of?
HIV genome
what other genes does HIV genome have that don’t affect lifecycle?
TAT REV
VPR
VIF
what do tatrev,vpr and vif do?
tatrev-regulates virus expression
VPR-cell cycle arrest
VIF-disrupts antiviral activity of APOBEC
what is tetherin?
human protein that inhibits retrovirus infection by preventing the diffusion of virus particles after budding from infected cells (BUT HIV also has a protein to counteract this)
where are viral membranes derived from?
host lipids etc
where does virus assembly take place?
usually virus replication site
what may some viruses that are exceptions require for assembly?
scaffolding proteins ie plant viruses
where are viruses with envelopes assembled?
surface of cell or subcellular compartments
what three things can membrane type and number affect?
1) spread around body (better)
2) one type can transmit from host to host well
3) one can replicate well
describe viral assembly briefly.
assembly is the simultaneous binding of the capsid protain and the viral genome. These assemble then this nucleoplasmid induces the assembly of envelope proteins for some viruses (on lipid bilayer). Budding then takes place leading to progeny virus with an envelope.
