Baltimore classification Flashcards
(22 cards)
What is the Baltimore classification
The Baltimore classification clusters viruses into families depending on their type of genome.
What are group 1
dsDNA viruses
What are the properties of Group one (dsDNA) viruses?
1) These types of viruses must enter the host nucleus before they are able to replicate
2) viruses require host cell polymerases to replicate the viral genome and, hence, are highly dependent on the cell cycle
3) Infection required cell to be in replication.
4) The virus may induce the cell to forcefully undergo cell division, which may lead to transformation of the cell
5) The mRNA is transcribed in the normal way from viral DNA using the host transcriptase enzymes, into two types of mRNA’s: 1) early mRNA, transcribed prior to the synthesis of viral DNA, and 2) late mRNA, transcribed from progeny DNA.
An example of a group 1 virus?
dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses, etc)
What are group 2?
ssDNA Viruses (+) sense DNA
What are the properties of Group two (ssDNA) viruses?
1) Most of them have circular genomes (the parvoviruses are the only known exception)
2) Eukaryote-infecting viruses replicate mostly within the nucleus, forming double-stranded DNA intermediate in the process.
An example of a group 2 virus?
Parvoviruses
What are group 3?
dsRNA viruses
What are the properties of Group three (dsRNA) viruses?
1) replicates in the “Core” capsid that is in cytoplasm
2) Replication is monocistronic and includes individual, segmented genomes, meaning that each of the genes codes for only one protein
An example of group 3 viruses?
Reoviruses
What are group 4 viruses?
(+)ssRNA viruses
What are the properties of Group four ((+)ssRNA) viruses?
1) + sense RNA stand - represents the polarity of the strand
2) do not depend that heavily on the cell cycle for replication
3) The replication of viruses happens in the cytoplasm
4) CAN be directly accessed by the host ribosomes to immediately form proteins
An example of group 4 viruses ?
Picornaviruses, Togaviruses
What are group 5 viruses?
(-)ssRNA viruses
What are the properties of Group five ((-)ssRNA) viruses?
1) - sense RNA stand - represents the polarity of the strand
2) do not depend that heavily on the cell cycle for replication
3) The replication of viruses happens in the cytoplasm or the nucleus
4) CANNOT be directly accessed by host ribosomes to immediately form proteins. Instead, they must be transcribed by viral polymerases into a “readable” form, which is the positive-sense reciprocal.
An example of a group 5 virus?
Orthomyxoviruses, Rhabdoviruses
What are group 6 viruses ?
ssRNA-RT viruses
Positive-sense single-stranded RNA viruses that replicate through a DNA intermediate
What are the properties of Group six (ssRNA-RT) viruses?
1) One defining feature is the use of reverse transcriptase to convert the positive-sense RNA into DNA
2) Instead of using the RNA for templates of proteins, they use DNA to create the templates, which is spliced into the host genome using integrase
3) Replication can then commence with the help of the host cell’s polymerases
Give an example of a group 6 virus?
Retroviruses
What are group 7 viruses?
dsDNA-RT virus
Double-stranded DNA viruses that replicate through a single-stranded RNA intermediate
What are the properties of Group seven (dsDNA-RT) viruses?
1) have a double-stranded, gapped genome that is subsequently filled in to form a covalently closed circle (cccDNA) that serves as a template for production of viral mRNAs and a subgenomic RNA
2) The pregenome RNA serves as template for the viral reverse transcriptase for production of the DNA genome.
Give an example of a group 7 virus?
Hepadnaviruses
