fundamental virology - L6A Flashcards
what is a virus?
a protein shell with genetic material
intracellular parasite
what is a virion?
extracellular form of a virus
what is a capsid
protein shell surrounding virus
what is a nucelocaspid
inner structure of protein + nucleic acid
what is an envelope
phospholipid bilayer (derived from host) + proteins
what is a lytic
viral infection that kills the host cell
what is lysogenic
viral infection where the virus genome integrates into host genome
name 4 ways virus’ spread
skin bites
blood transfusions
mucous membranes
breast milk
name 3 spreading ability factors
viability in environment
ability to survive in host
resistance to bodily sites
describe a naked virus
They lack n external membrane
described and envelope virus
has additional lipid coat derived from the host
give 2 examples of a naked virus
rhinovirus
poliovirus
enveloped virus examples
influenza
HIV
describe structure of virus
extremely small
contain few proteins in capsid
precise ordres
cannot be seen with convention microscope
how are viruses classified?
based on symmetry
what are the three classifications for viruses?
- helical
- icosahedral
- complex
how do we identify helical viruses?
length of nucleic acid
what do icosahedral viruses have
20 faces and 12 vertices
requires smallest number of capsomeres to build it
viruses can be complex structures with…
each part having own structure and symmetry
example of helical virus
tobacco mosaic virus
example of icosahedral
human papilloma virus
example of complex virus
bacteriophage T4
what protein do envelopes usually have and what does it do
spike protein
binds to and enter cells
how do viruses exit cells
budding
where they take a part of the host Plasma membrane with them
or cell lysis
what can classification of nucleic acid be
rna or dna
single or double stranded
example of RNA virus
HIV
example of a DNA virus
Hepatitis B
what can single stranded viruses be
plus
minus
what direction do plus stranded run in
5’ to 3’
what direction do minus stranded run in
3’ to 5’
what is plus and minus stranded also referred to
positive and negative sense
can DNA be transcribed immediately?
yes
what are the 7 categories of the Baltimore classification system/
double-stranded DNA viruses (Group I)
single-stranded DNA viruses (Group II)
double-stranded RNA viruses (Group III)
positive single-stranded RNA viruses (Group IV)
negative single-stranded RNA viruses (Group V)
positive single-stranded RNA viruses (Group VI)
positive double stranded DNA viruses (Group VII)
what do positive sense RNA genomes have
cap at 5’ end and poly A tail at 3’ end
used directly as mRNA
describe negative sense RNA genomes
first using a virus encoded RNA polymerase a positive sense RNA is made
this is then capped and polyadenylated
used directly as mRNA
can viruses metabolise?
no
what is an example of a key enzyme important for virus life cycle?
neuraminidase
name the stages for virions to be released
- attachment
- penetration
- nucleic acid and protein synthesis
- capsid assembly and genome packaging
- vision release
what is attachment
when the virus binds to the cell
what is penetration
injection of viral nucleic acid into host cell
what is nucleic acid and protein synthesis driven by
host under viral control
where does vision release occur
at the cell membrane in multiple ways
name the 4 growth phases of the viral life cycle
eclipse phase
maturation phase
what happens at eclipse phase
viral genome and proteins replicated
what happens at maturation phase
viral nucleic acid and mature viruses accumulate in cell
what is burst size
number of released viruses
what is burst size
number of released viruses
what changes during a lysogenic infection in virion release
after penetration, nucleic acid integrates into the host genome and called a prophage
cells divide and also replicate the viral genome
what are the 5 stages of a typical human infection
- binding and fusion
endocytosis
uncoating
replication ,translation and transcription
assembly and release
what are 2 consequences of a virus infection?
The infection can be PERSISTENT and not kill the cell but cause continual viral release by budding e.g. HIV
Some viruses can cause a normal cell to become cancerous and this is called TRANSFORMATION e.g. human papilloma virus
what is a retrovirus?
a virus that has RNA instead of DNA as its genetic material
which enzyme do retroviruses use
reverse transcriptase to become part of the host cells DNA
what must retroviruses make during life cycle
a DNA intermediate
