Introduction to Virology Flashcards
Viruses are responsible for ____ disease worldwide
50%
Why else are viruses important?
they are linked to 15-20% of cancers; they can be used as future tools for vaccines
Virus
disease causing entity at the boundary of life and non-life; all of nucleic acid genome; all are obligate parasites
Features of all viruses + features that some have
all = DNA or RNA + capsid some = matrix, lipid envelope, glycoproteins
Many viruses use what type of capsids
icosahedral, with 3 capsomeres per face and a minimum of 20 faces
2 examples of naked capsid viruses
bacteriophage and adenovirus
you can classify viruses by nature of capsid
naked capsid (which can be helical or icosahedral) or enveloped (which can be helical, icosahedral, or complex)
you can also classify by nature of genome
DNA or RNA (which both break down into SS or DS)
Group IV viruses are + strand RNA viruses…what does this mean for their infectivity and replication strategy
the positive strand RNA is infectious because it can be introduced into the cell and directly translated into proteins
replication strategy- they will make a negative strand to serve as a template for making more positive strands
Group VI viruses like HIV have a particular genome that leads to their replication strategy…
they have a positive stranded RNA with extra sequences for genome amplification and packaging…reverse transcription into dsDNA is a must
Group III viruses are weird (rotavirus = example)…
they come in a vesicle, they have their own RNA-dependent RNA pol, they make a positive strand which leaves the vesicle to be packaged or translated. In a capsid, the positive strand is used to make a negative strand (hence dsRNA). The cells can’t melt the dsRNA (which is good because you want the cells to be very good at recognizing dsRNA as foreign to maintain the IFN-innate response) but the viral enzymes can.
sense strand
mRNA made from the DNA template strand (the anti-sense strand)..it is the positive strand and it will read directly the same as the complementary DNA strand to the template
So, if you have a positive mRNA sense strand, you can find the DNA template by matching the complementary bp to it
Negative strand viruses must
have their RNA copied by a RNA dependent pol into a positive sense strand- it is am amplification step to make lots of mRNA and lots of protein
Picornaviruses (polio) and flaviviruses (west nile, dengue)
genome = positive-strand RNA
virion RNA dependent polymerase? no
initial event in cell= translation
genome infectivity = infectious
orthomyxovirus (flu) and paramyxovirus (measles and mumps)
genome = negative-strand RNA
virion RNA dependent polymerase? yes
initial event in cell = transcription
genome infectivity = non-infectious
reovirus (rotavirus)
genome = ds RNA
virion RNA dependent polymerase? yes
initial event in cell = transcription
genome infectivity = no