lecture 7 Flashcards
Replication of Viruses
- do not have genetic capability to multiply by division
- hijacks and utilizes host cell machinery to produce its proteins and nucleic acid for next generation of virus
- process of virus replication in host cell resembles assembly line
permissive cell
cell is which a virus is able to replicate
the cell machinery supports replication of the virus
non-permissive cell
cells in which a factor or factors necessary to viral reproduction is not present or one detrimental to viral reproduction is absent
eg. absence of appropriate receptors
MOI (multiplicity of infection)
refers to the number of virions that are added per cell during infection
latent period
after uncoating and till just before 1st appearance and release of extracellular new virus particle
no extracellular virions detected
eclipse period
after uncoating and till just before first appearance of intracellular new virus progeny particles
adsorption
during this period virus attaches to and enters cell, titer of free virus in medium may decline
burst size
number of infectious virions released per average cell
virus attachment
- attachment to receptor/s on host cells is/are very specific, lock and key like
- each virus has its own specific receptor/receptors on specific host cells
attachment to the host cell surface
- mediated by interaction between the virus and complimentary receptor on host cell surface, cell that lacks appropriate receptor escape being infected by virus
- some cases, binding to cellular receptor is not sufficient for infection, additional cell surface molecule, or co-receptor required for entry
- some viruses may use more than one host cell receptor, such as HIV
co-receptor
in some cases, binding to a cellular receptor is not sufficient for infection
-additional cell surface molecule, or co-receptor is required for entry
viruses can enter the host cell using any receptor present on surface of host cell
T/F
F
penetration /uncoating of non-enveloped/naked viruses
- receptor mediated endocytosis (commonly seen)
2. pore mediated penetration (in some naked viruses)
penetration and uncoating of enveloped viruses (depends on type of fusion protein)
- surface membrane fusion (have pH independent fusion protein)”
- receptor mediated endocytosis (have pH dependent fusion protein)
other/ uncommon methods of entry into host cell
-antibody- mediated attachment and penetration, as in FIPV
Virus penetration in many non-enveloped viruses
-Clathrin-mediated endocytosis or receptor-mediated endocytosis of virus by host
less common virus penetration in non-enveloped viruses
pore-mediated penetration of viral genome into host cell
surface membrane fusion of enveloped viruses
- fusion of virus envelope with host cell membrane occurs directly on surface of host cell
- facilitated by pH independent fusion protein
receptor mediated endocytosis of enveloped viruses
- pH dependent fusion protein
- fusion of virus membrane with host endosomal membrane release viral genome
- fusion protein requires low pH to be activated which is achieved in the endosome
True/false antibody mediated attachment is used by viruses to penetrate the host cell
true
virus uncoating
- release of viral genome into the host cell
- virion can no longer be detected
uncoating results in…..
loss of infectivity of virions
functions of the parent virus in the host cell
- produce multiple copies of new viruses (children/progeny)
- produce viral proteins for capsid and successful replication
reverse transcriptase
converts viral RNA to cDNA during virus replication
processing of primary RNA transcript (Pre-mRNA)
- viral mRNA must conform to requirements of host cell translation system i.e the host cell can recognize mRNA and translate
- series of modification occurs known as processing of primary RNA transcript/pre-RNA
- after processing mRNAs are translated into the cytoplasm
- viral mRNAs produced in the nucleus must also be exported to the cytoplasm
processing of primary RNA transcript (Pre-mRNA)
- capping
- addition of 3’ poly-adenylated tails
- splicing
capping
-addition of 7-methylguanosine to the 5’ end of RNA
RNA splicing
process which removes introns (non-coding region) and joins exons (coding region) in primary transcript
monocistronic mRNA
mRNA that encodes one polypeptide
polycistronic mRNA
mRNA encodes several polypeptides
assembly and maturation
- assembly of virus genome and proteins into new virions follow a specific order
- all components, including nucleic acids and proteins, are packaged to form mature virions
- may take place in nucleus, cytoplasm, plasma/ cell membrane (most enveloped viruses)
naked virions release progeny by….
lysis of host cell (cannot exit by budding because they lack envelope)
enveloped virions release progeny by….
budding through the plasma membrane
exocytosis
viruses that acquire envelope while budding from ER, golgi apparatus, or nuclear/nucleus membrane leave infected host cell by exocytosis
replication of retroviruses uses….
- reverse transcriptase (synthesizes RNA into DNA)
- integrase (integrates viral DNA to host genome)
viruses can acquire the lipid envelope only from the cell membrane of infected host cells?
T/F
F
methods of cell-to-cell spread of viruses
- extracellular spread
- intercellular spread
- nuclear spread of virus genome
intercellular spread
results in rapid virus dissemination, evasion of immune system, and persistent infections
