Virology1 Flashcards
briefly explain the history of virology
- filterable agent infectivity for TMV & foot and mouth disease virus
- first human virus described causes yellow fever
- filterable viruses = Rinderpest, Vaccinia, Rabies, Cassava mosaic
- Avian leukosis & poliomyelitis & chicken sarcomas shown to be caused by viruses
- bacterial viruses discovered
- spanish flu pandemic
what are 6 characteristics of viruses?
- small & infectious (20nm - 300nm)
- acellular pathogens
- obligate intracellular parasites (host & cell-type specificity)
- DNA/RNA genome (never both)
- lack genes for products needed for reproduction
- infect all types of cells
what is a virus’ genome surrounded by?
protein capsid (sometimes a phospholipid membrane w viral glycoproteins)
what are virions?
virus particles viruses reproduce through the exploitation of host-cell genomes
what are capsomers?
- small structural unit that makes up a capsid
- are an outer covering for the protection of the genetic material of a virus
what is a nucleocapsid?
capsid + genome
what are peplomers?
viral proteins that modify a virus envelope that was acquired from nuclear or plasma membrane of the infected host cell
what are the arguments for viruses being non-living? (4)
- acellular
- no cell nucleus, organelles or cytoplasm
- can’t move
- can’t reproduce
what are the arguments for classifying viruses as living? (4)
- can only reproduce in living cells
- obligate intracellular parasite
- can evolve
- genetic material
what type of microscope do you need to see viruses?
electron microscope
what’s the difference between the phylogeny of viruses and bacteria?
viruses → tangled
bacteria → natural
do viruses have ribosomes?
no
what are naked (nonenveloped) viruses ?
viruses that don’t have an envelope
what type of capsid structure is found in enveloped and nonenveloped viruses?
enveloped = helical
non enveloped & enveloped = icosahedral
which type of DNA virus isn’t icosahedral?
poxvirus
what are 3 characteristics of RNA viruses?
- ss/self-duplicating RNA
- high mutation rate
- all plant viruses
explain positive/negative sense of RNA
Positive sense (+sense) RNA = mRNA
Negative sense (-sense) RNA = Requires RNA polymerase to be converted to +sense RNA
what are 3 characteristics of DNA viruses?
- DNA dependent and replicate using DNA pol
- dsDNA but sometimes can be ssDNA
- most animal viruses are DNA viruses
what are 3 types of viruses (ito what they infect)?
what type of genetic material does each type have
- animal viruses → DNA or RNA
- plant viruses → RNA
- bacteriophage → DNA
what are the different ways in which viruses can be transmitted?
direct contact, indirect contact with fomites or through a vector (mechanical or biological)
what are zoonoses and reverse zoonoses?
zoonoses → transfer from animal to human
reverse zoonoses → transfer from human to animal
what are the four viral structures?
+ describe them
- helical (nucleic acid is spiral w capsomers helically around coil)
- icosahedral (spherical shape w nucleic acid inside capsid, composed of 20 triangular faces)
- spherical (round & some have spikes)
- complex (don’t confirm into any category i.e. bacteriophages, poxvirus)
what does a species, genus, subfamily, family and order refer to?
- species → pop of viruses that share distinct pool of genes
- genus → group of related viral species
- subfamily → group of related viral genera
- family → group of a related subfamily
- order → group of family
what are the 3 criteria for clasification of viruses?
+ brief explanation
- morphology (size & shape, presence of envelope)
- structural protein (contributes to molecular weight of virion)
- nucleic acid properties (ds/ss, positive/negative sense sequence)
what do segmented genomes do?
facilitate exchange of genome segments between different virus strains during coinfection of a single host cell (viral reassortment)
what are the 2 major priorities of the virus life cycle?
- make viral proteins
- make copies of the viral genome
what are the different polymerases and what do they do?
- DdDp DNA dependent DNA pol = synthesises DNA from DNA (DNA → DNA)
- DdRp DNA dependent RNA pol = synthesises RNA from DNA (DNA → RNA)
- RdRp RNA dependent RNA pol = synthesises RNA from RNA (RNA → RNA)
- RdDp RNA dependent DNA pol = synthesises DNA from DNA (RNA → DNA) (REVERSE TRANSCRIPTASE)
what is the baltimore scheme?
a system that divides viruses into genome type and the mechanism of mRNA production
what are class i viruses?
+ examples + type of enzyme (pol)
ds DNA
mRNA transcribed directly from DNA template
e.g. herpesvirus, adenovirus, most bacteriophages
dddp → copy + & - to produce dsDNA
ddrp → copy - into mrna → into proteins using host’s ribosomes
what are class ii viruses?
+ examples
ssDNA
DNA coverted to double stranded before RNA is transcribed
e.g. canine parvovirus
dddp → copy + to produce dsDNA intermediate
ddrp → copy - strand of dsdna intermediate to produce + viral mRNA → translated into viral protein
dddp → copy - dsdna intermediate strand to produce ss(+) DNA viral genome
what are class iii viruses?
dsRNA
mRNA transcribed from RNA genome
e.g. rotavirus (childhood gastroenteritis)
rdrp → copy both + & - to produce dsRNA genome
rdrp → copy - into + viral mRNA → translated into viral proteins
what are class iv viruses?
+ examples
ssRNA (+)
genome functions as mRNA
e.g. coronavirus, pircornavirus (common cold), polio
rdrp → copies + to produce -ssRNA → rdrp copies - to produce +ssRNA
viral genome translated into viral protein
class v viruses
+ examples
ssRNA (-)
mRNA transcribed from RNA genome
e.g. rabies or influenza
rdrp → copies - RNA to produce +ssRNA → rdrp copies +ssRNA to produce -ssRNA viral genome
rdrp → copies -RNA to form + viral mRNA → translated into viral proteins
class vi viruses
+ examples
ssRNA viruses w reverse transcriptase
reverse trans → makes ssDNA from RNA genome → DNA incorporated into host genome → mRNA transcribed from incorporated DNA
e.g. HIV
reverse transcriptase possesses ribonuclease activity → degrade RNA strand of RNA-DNA hybride
reverse transcriptase → used as DNA pol to yield dsDNA → insert into host = provirus
class vii viruses
+ examples
dsDNA w reverse transcriptase
DNA is replicated thru RNA intermediate (may serve directly as mRNA or template to make mRNA)
e.g. hepatitis B virus
what is a provirus?
can remain latent indefinitely or cause expression of viral genes, leading to production of new viruses
