V2&3: Virus replication Flashcards
(26 cards)
How do viruses recognise host cells?
Viruses have glycoproteins that stick out & bind to receptors on host cells.
What is the purpose of attachement factors for viruses?
They can help to concentrate viruses on host cell’s surface.
What is the difference between co-receptor & attachement factors?
A co-receptor will lead to a conformational change, but attachement factors do not necessarily lead to conformational changes.
How do viruses enter host cells?
By endocytosis
Why is endocytosis used for virus entry?
Allows virus to go wherever it wants
Allows for compartmentalised environments used by the virus to trigger conformational changes/trigger lysis/change permeability
How do envelopped viruses penetrate host cells?
By membrane fusion
How do naked viruses penetrate host cells?
By pore formation/membrane disruption.
What is the principle of the Baltimore classification for viruses?
It classifies viruses according to their genetic material (whether they are DNA or RNA, single or double stranded, etc).
What is class I of Baltimore classification?
ds DNA viruses
What is class II of Baltimore classification?
ss DNA viruses
What is class III of Baltimore classification?
ds RNA viruses
What is class IV of Baltimore classification?
+ve ss RNA viruses
What is class V of Baltimore classification?
-ve ss RNA viruses
What is class VI of Baltimore classification?
retroviruses that have ss +ve RNA
What is class VII of Baltimore classification?
ds DNA viruses that use reverse transcriptase to replicate.
How do class I viruses replicate?
DNA is copied & transcribed to mRNA
RNA is transcribed to proteins
Viral proteins + DNA genome = virion
How do class II viruses replicate?
ss DNA is copied to ds DNA
ds DNA is translated to RNA
RNA is transcribed to proteins
ds DNA is separated into 2 strands by helicase
ss DNA + viral proteins = virion
How do class III viruses replicate?
ds RNA translated to mRNA
mRNA translated to proteins + forms ds RNA
ds RNA + viral proteins = virion
How do class IV viruses replicate?
+ve ss RNA translated to protein
+ve ss RNA forms complementary -ve ss RNA
+ve & -ve RNA strands dimerise & RNA-dependent polymerase is used to make ds DNA
ds DNA is transcribed to +ve ss RNA
+ve ss RNA + viral proteins = virion
How do class V viruses replicate?
-ve ss RNA made into mRNA + complementary +ve ss RNA formed
mRNA translated to proteins + new -ve ss RNA formed
-ve ss RNA + viral protein = virion
How do class VI viruses replicate?
+ve ss RNA made into -ve ss DNA using reverse transcriptase
-ve ss DNA then made to ds DNA that is integrated into host’s genome
How do class VII viruses replicate?
ds DNA forms mRNA
mRNA translated to viral transcriptase
mRNA reverse transcribed to ds DNA using reverse transcriptase
ds DNA + viral proteins = virion
What are the methods used by viruses to exit cells?
Budding is used mostly envelopped viruses & some non-envelopped viruses
Virus-induced cell lysis is used by most naked viruses
Membrane scission is also used
How does budding (for virus exit of cells) occur?
Budding requires at least 1 viral protein, at least 1 viral matrix protein & the viral genome.
Viral membrane proteins are translated on rER & get transferred to membrane via secretory pathways.
Cytoplasmic tails of these viral membrane proteins recruit the genome & other viral proteins.
Virus just buds off the membrane.
