VIROLOGY 3 - GENOME CLASSIFICATION Flashcards
what does baltimore classification do
categorises animal viruses based on their modes of replication and transcription in eukaryotic cells
how is viral mRNA made into proteins?
the viruses use the host machinery, the ribosomes, to make their viral proteins
what are the 7 baltimore classes of viruses?
I. dsDNA viruses
II. (+) ssDNA viruses
III. dsRNA viruses
IV. (+) ssRNA viruses
V. (-) ssRNA viruses
VI. ssRNA -RT viruses (+) RNA viruses that replicate through DNA intermediate
VII. dsDNA RT viruses: dsDNA viruses that replicate through RNA intermediate
class VI and VII require RT
characteristics of Class I?
dsDNA viruses
example: herpesviruses
similar to replication of cellular DNA
viral proteins made in cytoplasm
viral genome replicated in nucleus
transcription: dsDNA is immediately transcribed into mRNA using host RNA pol.
except pox virus that use their own Dd RNA pol.
replication: use host machinery
characteristics of class II viruses
ssDNA viruses, example is parvoviruses
cells do not use ssDNA, rarely infect humans because we have cell sensors
transcription: viral mRNA is made from dsDNA using host transcription machinery
replication: most of these viruses have circular genomes that are replicated within nucleus via dsDNA intermediate, require host DNA pol. to make the complementary strand
new replicated strand is released as ssDNA
how do RNA virus genomes make sure that RdRp can be used?
mammalian cells do not have RdRp
RNA viruses either carry or encode it
RdRp makes RNA genomes and mRNA from RNA tempaltes
characteristics of class III?
dsRNA virus
example: rotavirus
all happens in the cytoplasm
RdRp needed to make mRNA and make copies of the genome
class III viruses carry RdRp in the viral particle
characteristics of class IV?
(+)ssRNA genome
example: covid, poliovirus, HCV
all happens in cytoplasm
transcription: (+) RNA can be used directly to make proteins by host ribosomes
genome carries RdRp
replication: made by RdRp, makes the (-) complementary strand, used as a template to then make more of the (+) strand
characteristics of class V?
(-) ssRNA
example: influenza
all happens in cytoplasm
(-) ssRNA cannot be used by ribosomes
transcription: carry RdRp to make mRNA
replication: (+)ssRNA is then used as a template for replication of more copies of (-)ssRNA
characteristics of class VI?
ssRNA RT viruses
example: HIV
uses RT to make (+)RNA into dsDNA in the cytoplasm
carry RT in the viral particle
insert dsDNA intermediate in the host genome in nucleus using viral enzyme that it carries, integrase
that becomes the provirus
transcription: integrated provirus used as a template to make mRNA by host cell
replication: provirus used as template to make (+)ssRNA by host
characteristics of class VII?
DNA reverse transcribing viruses or pararetroviruses
example: hepatitis B
partially dsDNA (happed DNA)
converted to fully dsDNA by cellular DNA repair mechanisms or forms a covalently closed circular DNA (cccDNA)
transcription: dsDNA is transcribed into mRNA in nucleus
replication: uses ssRNA intermediate as template for RT to make more DNA in the cytoplasm
encode for RT
summary table, should be able to fill this out, the rows are the 7 classes and the columns are: how is mRNA synthesized and what molecule is the template for genome replication?
compare and contrast the transcription methods of different classes?
how do viruses from classes I, II, IV and VII generate the dsDNA template to make their mRNA?
what are the two ways in which classe III, IV and V use RdRp?
how do classes IV and VI use different enzyme to express and replicate their genome?
