Virus replication Flashcards
process of viral rep requires ?
assembly line
permissive cell
cell in which virus is able to replicate; cell machinery supports replication of the virus
non permissive cell
+ 2 types
factors necessary to viral reproduction are not present
1. virus cant enter/attach/infect
2. virus gets in but conditions dont support reproducing
Multiplicity of infection MOI
number of virions that are added per cell during infection
eclipse period
after uncoating until we see the first virus intracellularly
latent period
uncoating to newly formed virus particle extracellulary
One step virus growth curve (3 phases)
- adsorption: virus attaches and enters cell, titer of free virus in the medium may decline
- eclipse period: time between uncoating and appearance intracellularly of first virion
- latent period: time before new virus appears in the medium – no extracellular virions are detected
burst size
number of infected virions released per average cell
steps of viral replication
attachment - penetration - uncoating - synethesis of viral nucleic acid and capsid - assembly and maturation - release in large numbers
Viral attachment
-very specific, like lock and key
-each virus has its own receptor on specific host cells
-mediated by interaction between virus and complimentary receptor on host cell (if cell lacks receptor = was not infected by virus)
-some cases: binding to cellular receptor is not sufficient for infection: additional surface molecule (co receptor) must be added
what virus uses more than one host cell receptor to enter?
HIV
co receptor
binding to cellular receptor is not sufficient for infection, additional cell surface molecule is required for entry because it strengthens bond between host cell and viral cell
virus penetration and uncoating: nonenveloped vs enveloped viruses
other methods of entry
nonenveloped: receptor mediated endocytosis, or pore mediated penetration
enveloped - depends on type of fusion protein which decides how enveloped virus will infect cell
- surface membrane fusion (have pH indep. fusion protein) or receptor mediated endocyt. (have pH depent. fusion protein)
other method: AB mediated attachment and penetration - FIPV
non enveloped virus endocytosis
clathrin-mediated endocytosis or any other receptor mediated endocytosis of virus by host
OR
pore mediated penetration of viral genome into host cell- viruses inject genome into host cytoplasm through creation of a pore in the host membrane
enveloped viruses
surface membrane fusion with pH INDEPENDENT fusion protein: fusion of virus envelope with host cell membrane occurs directly on surface of host cell
OR
receptor mediated endocytosis with pH DEPENDENT fusion protein: fusion of viral membrane with host endosomal membrane release viral genome - fusion protein needs low pH to get activated and then allows viral envelope fusion with membrane
AB mediated attachment
feline infectiou peritonitis FIP virus
FIP virus enters host macrophage by attachment of its spike proteins to the CD13 receptor
virus uncoating definition
release of viral genome in host cell = virion can no longer be detected
UNCOATING = loss of infectivity of virions
viral protein and nucleic acid synthesis:
parent virus leads to what 2 outcomes
function 1: multiple copies for new viruses (children)
function 2: viral proteins for capsid and successful replication
reverse transcriptase
conversion of viral RNA to cDNA during viral replication
processing of primary RNA transcript (pre RNA)
viral mRNA must conform to requirements of host cell translation system so the host can recognize the viral mRNA and translate it
modifications of processing primary RNA transcript/pre RNA (3)
- after processing, where are mRNAs translated
- capping
- poly A tail
- splicing
CYTOPLASM, viral mRNA produced in the nucleus must also be exported to the cytoplasm
Capping
Poly A tail
capping: Addition of 7-methylguanosine to 5’ end of RNA
Adding 3’ poly adenylated tails
Splicing: removes introns and joins exons in a primary transcript
intron
exon
portion of gene that does not code for AA
portion of gene that codes for AA
2 types of splicing
- consecutive splicing: every intron is spliced out, every exon is spliced in
- alternative splicing: all introns spliced out, only selected exons spliced in, resulting in mRNA having different coding information derived from a single gene
2 types of viral mRNA
- monocistronic = mRNA that encodes 1 polypeptide
- polycistronic = mRNA that encodes several polypeptides
assembly and maturation
-3 places where it could take place
= assembly of virus genome and proteins into new virions follow a specific order
- components packaged to form mature virions
-could take place in nucleus, cytoplasm or plasma/cell membrane (most enveloped virus)
releasing progeny viruses (2 diff ways)
- naked virions - lysis of host cell (when host cell ruptures, lets viral particles out)
- enveloped virions - budding
naked virions cannot exit host cell by budding because they LACK an envelope
exocytosis
viruses mature by budding through the membranes of the golgi, nuclear membrane or ER, vesicles containing virus then migrate to the plasma membrane and are released by exocytosis because already inside the cell
replication of retroviruses (2 steps)
- reverse transcriptase: RNA to DNA
- integrase: integrates viral DNA into host genome
cell to cell spread of viruses (3 types)
- Extracellular spread - released viruses travel extracellularly
- intercellular spread, viruses pass through intracellular junction between cells - results in rapid virus dissemination, evasion of immune system and persistent infections EX: HERPES
- Nuclear spread of virus genome
