virus replication Flashcards
what are the three phases of viral replication?
initiation of infection, replication + expression, and release of mature virions
which two experiments provided evidence for viral replication?
Ellis &; Delbruck 1939 single burst experiment, and Hershey &; Chase 1952
how did Ellis & Delbruck provide evidence for viral replication?
1- added bacteriophage particles to a culture of rapidly dividing bacterial cells
2- diluted culture after a few minutes to synchronise the cells
3- took samples and analysed them by plating on agar and bacterial lawn
the results showed stepwise increase in phage concentration
how do you calculate the total phage titre including intracellular phages?
disrupt the bacteria with chloroform
what is meant by eclipse period?
after dilution of culture, there is a period of 10-15 mins where no phage is detectable
what is the latent period?
the time before the first extracellular virus particles appear
what is attachment?
specific binding of a virus attachment protein to a cellular receptor molecule
what can host cell receptors be?
proteins or carbohydrate side chains on glycoproteins or glycolipids
why are protein host cell receptors more specific?
the same arrangement of sugar side chain may be prsesent on multiple types of cell
how does penetration differ from attachment?
usually energy dependent
by which mechanisms can penetration occur?
translocation of the entire virus across the cytoplasmic membrane - rare
endocytosis of the virus into intracellular vacuoles - common
fusion of the virus envelope with the cell membrane
what is meant by uncoating?
virus capsid is completely or partially removed and the virus genome is exposed, usually in the form of a nucleoprotein complex
what is the role of virus fusion proteins?
promote fusion between virus envelope and the endosomal envelopes
what is assembly?
involves collection of all the components necessary for the formation of the mature virion
what are lipid rafts?
membrane microdomains enriched with glycolipids, cholesterol and a specific set of associated proteins
what are inclusion bodies?
subcellular components full of newly synthesised structural components
what is maturation?
the stage in the replication cycle where the virus becomes infectious. usually involves structural changes in the virus particle that may result from specific cleavages of capsid proteins
why is it desirable for a virus to encode its own proteases for maturation?
cell proteases can lack specificity and destroy the whole capsid
what is budding?
the process by which enveloped viruses leave the cell, they acquire their envelope from the host cell membrane or an intracellular vesicle
how does genome replication occur for class I viruses?
with the exception of poxviridae, replication is exclusively nuclear
how does genome replication occur for class II viruses?
replication occurs in the nucleus and involves the formation of a ds intermediate which serves as a template for the synthesis of single stranded progeny
how does genome replication occur for class III viruses?
these viruses have segmented genomes, each segment is transcribed separately to produce individual monocistronic mRNAs
how does genome replication occur for class IV viruses with polycistronic mRNA?
genomic RNA forms mRNA which is translated into a polyprotein and cleaved
how does genome replication occur in class IV viruses with complex transcription?
two rounds of translation of subgenomic RNAs are necessary to produce genomic RNA
how does genome replication occur in class V viruses with non-segmented genomes?
the first step is transcription of the - sense RNA genome by the virion dependent RNA polymerase to produce monocistronic mRNAs, these also serve as the template strand for subsequent
what occurs during viral assembly?
- involves collection of all the components necessary for the formation of a mature virion
- the basic structure of the virus particle is formed
what occurs during viral maturation?
-the virus becomes infectious, this usually involves structural changes in the virus particle which originate from specific cleavages of capsid proteins
why is it important for maturation that viruses encode their own proteases?
relying on host proteases could cause the entire capsid to be destroyed
what are the two methods in which a virus is released?
lysis - infected cell breaks open
budding - enveloped viruses acquire their lipid membrane as the virus buds out of the cell
what occurs during the attachment stage of virus replication?
the virus binds to a host cell receptor
