Intro to viruses Flashcards
describe a virus briefly.
a small non cellular agent consisting of a nucleic acid with a protein coat requiring a host cell for reproduction
what 7 things were usually used to classify a virus as non-living?
1) small physical size
2) small genome
3) obligate parasite
4) cannot grow
5) no respiration or metabolism
6) no ribosomes
7) capsid (protein coat)
Why did the discovery of the Pandora virus blur the lines of life for viruses?(3)
The pandora virus is bigger than microplasma bacteria,it’s genome is bigger than some archaea and bacteria and it does not have a capsid (but it also doen’t have ribosomes)
Why is it thought some viruses have a metabolism?
some viruses have genes for metabolic processes and tRNA for lipid biosynthesis. No REAL metabolism but they can physically change their surroundings
where do viruses get protein for capsid?
host protein
although viruses cannot grow how do they produce copies of themselves ?
self-assemblage
Do most RNA viruses have single stranded DNA? exception?
Yes, apart from reovirus (dsRNA)
what is unusual about Parvovirus?
it is a ssDNA virus
do most DNA viruses have dsDNA?
yes
what is interesting about Reovirus?
it is a dsRNA virus
what are the two types of ssRNA viruses?
+sense and - sense
can you translate directly from - sense ssRNA?
no, you must make + before you translate
what viruses have circular DNA?
some viruses, e.g Bacteriophage (has Ori)
Do most viruses have linear genomes?
yes most are linear
Are RNA genomes typically small?if so why and what is their max size?
yes max 30kb as RNAP has less proofreading (if bigger progeny have too many mutations and are defective)
Define Quaisi species
the fact the virus exists of a pool of sequences and this is why they are difficult to make vaccines for
what is this a definition for? group of viruses related by a similar mutation or mutations, competing within a highly mutagenic environment.
Quaisi-species
what are 4 RNA virus examples?
Polio,Rubella,Yellow fever and measles
what are 3 DNA virus examples?
Hepatitis,Herpes and mimivirus
What is interesting about the mimivirus?
it is very large,it’s genome size overlaps bacterial genome sizes
what can + viruses do?
make protein directly
what does non-segmented mean?
only one “chromosome”
what does segmented mean, wrt viral genomes?
multiple ‘chromosomes’.
what does zoonotic mean?
infectious diseases of animals that can be naturally transmitted to HUMANS
zoonotic diseases are generally worst for the first host? T/F
false they are usually worst for the second host. Ebola=fatal for humans
what is the mimivirus related to?
closely related to othetr viruses such as the POX virus but it is extremely large
what is the mimivirus genome size and how many genes does it have?
900 genes, 1mbp
is the pandora bigger than mimi?
Yes
what do vectors for animals and plants usually have?
biting mouth parts
do viruses usually jump between related species or distantly related species?
closely related species. It is easier to switc hspecies than change receptors
population density may also make vectors more common for example:
rodents may have high population density rather than expected monkeys
what is an example of a very simple virus consisting of only a genome surrounded by a capsid?
TMV, tobacco mosaic virus.
what do some viruses have in addition to a capsid?
a lipid membrane
what is an example of a virus with a capsid and a lipid membrane?
Retrovirus HIV-1
what is the symmetry of the capsid a result of?
self assembly folding; 5 fold,3 fold or 2 fold.
what type of genome do most animal viruses have?
ssRNA
what is common in RNA structures?
a secondary hairpin loop that makes a small area of dsRNA
why did ebola cause 90% mortality?
The virus affects many cells and unlike others only 1 virus is needed for infection
what do smallpox and polio have in common?
they are host specific
why was polio easy to eliminate?
it is an RNA virus yet it is not present as a quaisi-species
What does WNV stand for?
WNV (humans are dead end, not transmitted back to mosquitoes)
DOES VIRULENCE INCREASE OVER TIME?
no it decreases
how do you find the natural host (natural reservoir)?
the natural host is usually not dead so you should go to location of outbreak and surrounding areas,could trap certain species (closely related or of high density) e.g in ebola case this was monkeys,bats and rodents) the PCR and build phylogenies (3 species of bat had similar viruses), then correlate host range with outbreak range.
how many genes does the pox virus have?
250
is the mimivirus a dsDNA virus?
yes
what do we mean when we say the capsid is differentiated?
it consists of several proteins
e.g filoviruses
what is an example of a virus with a genome of less than 4000 bp?
parvovirus
what size are HIV genomes?
9kb
what type of viruses can have overlapping genes?
small ones e.g HIV-1 and HIV-2
when do antigenic shifts occur and what are they?
occur when RNA segments are exchanged between viral strains in a secondary host. Can lead to virus expressing novel proteins.
Give an example of when antigenic shift has caused a pandemic strain of influenza?what was produced and why was this bad?
when a pandemic strain was created through a mix of avian,human and swine influenza and this lead to the production of new HEMAGLUTININ. Massive effect because humans had no cross protective immunity
what type of genomes can usually undergo antigenic shifts?
+ sense strands of small genomes in 5’-3’ direction, usually segmented
What type of genetic recombination can occur in unsegmented viruses?
homologous recombination
how can non-segmented viruses evolve? (3)
1)mutation 2)recombination 3)antigenic shifts
what are retrovirus genomes?
+ sense non segmented
what are influenza viruses?
-ve sense viruses with segmented RNA genomes (7/8 segments depending on the virus)
what is an advantage of re assortment in segmented H3 virus (made from avian H3 and avian H2)?
can produce at least one protein per segment if not more
in segmented does one segment usually code for one protein?
yes
