lecture set 4 banfield Flashcards
what animal is one of the only animals to not have disease related with the herpes virus?
sheep
true or false, the natural host reservoir of a virus is often not harmful, but if the virus jumps to a different species it is.
true, e.g. a zebra herpes virus killed a polar bear at a zoo
explain the shared properties of ALL herpes viruses.
- spherical, enveloped virions
- icosahedral capsid with 162 capsomeres
- lipid envelope with many glycoproteins (10 - 12)
- linear dsDNA
- 70-200 genes
explain the alpha proteins of the herpes virus
herpes virus has a sequential transcription. alpha protein genes are turned on first which help the virus evade the host immune response and regulate the viruses further gene expression
what class of proteins are the alpha proteins?
they are called the kinetic class (transcribed quickly)
explain beta proteins in herpes transcription
proteins for nucleotide metabolism and genome replication
explain gamma proteins of herpes virus transcription
gamma proteins are structural proteins required after genome replication
t or f, herpes viruses establish latency where few of their genes are expressed. they can be reactivated to become infectious.
true,
explain the transmission of herpes viruses
herpes particles are very fragile outside of cells and therefore require close transmission. Typically by skin to skin contact. in crowded areas such as where livestock live, sneezing and droplet spread can transmit it too.
explain alpha herpesviruses
- they replicate quickly, within 12 hours
- they infect the skin then go up axons and establish latency in neurons.
- they lyse the cells they infect
- some have a broad range of hosts
what 2 viruses are prototype alpha herpes viruses?
herpes simplex virus 1 and VZV
what is the leading cause of blindness?
HSV1 reactivation in the eye
explain beta herpesviruses
- they grow very slowly (80-20 hours)
- they become latent in lymphocytes and monocytes
- they take several days to lyse the cells they infect
- they have a restricted host range
t or f, HCMV and VZV are both common beta herpesviruses
false,
HCMV = Beta
VZV = alpha
explain gamma herpes viruses
- restricted host range
- infect (and can transform) B lymphocytes
- only herpes virus that can cause cancer
there are 8 human herpes virus where humans are the natural host. there is an additional pseudo one. what is this 9th one?
monkey B virus
t or f, Monkey B virus is very pathogenic to humans
true, it infects pseudo bi-polar neurons allowing it to go the brain
what are tegument proteins
they are proteins that are beteen the viral envelope and the nucleocapsid which act as a middle layer. They are often involved in evasion of the host immune response
explain how HSV attaches and enters to host cells
- glycoprotein D is important in binding the cell receptors
- then 4 glycoproteins form a complex which leads to fusion with the cell membrane
- hsv capsid and tegument proteins are released into the cell (tegument set up internal environment of cell)
- hsv capsid binds a microtubule for transport
explain how the HSV gets its genome into the nucleus
- after binding the microtubule, motor proteins take it to the nucleus where it docs to a nuclear pore
- since the DNA is packaged at a very high pressure, upon this binding the capsid opens and injects the DNA.
- the linear dsDNA becomes circular once in the nucleus.
what is VP16?
a very potent and well known transcription factor which is in the herpes tegument. it enters the nucleus and acts on the circular DNA when it enters.
explain DNA replication and gene expression in the HSV.
VP16 acts on the DNA to create transcripts for alpha proteins. the translated alpha proteins will aid in immune evasion and they will be transcription factors for beta genes to turn on. the translated beta proteins are responsible for DNA replication which now begins. The circular DNA gets converted into whats called concatameric DNA which is transcribed to make gamma proteins for capsid synthesis
where does the HSV replicated DNA get packed into the nucleus? how does this occur?
- occurs in the nucleus
- it gets fed through the UL6 portal
what is concatemeric DNA molecules?
this the REPLICATED DNA that transcribes for gamma proteins and gets packaged into the capsid
what are the three components of the HSV capsid
hexamers
pentamers
triplexes
Explain HSV egress.
once the Concatemeric DNA has been fed into the capsid egress occurs.
- the capsid interacts with two proteins which form an “egress complex” this leaves into the perinuclear space in an endosome.
- Endosome fuses with the nuclear membrane and capsid + proteins enter the cytoplasm
- Capsid goes to the golgi where TGN proteins interact with capsid glycoproteins to coordinate the budding rxn.
- now infectious, the HSV leaves the golgi forming an outer endosome
- this fuses with the PM to expel the enveloped HSV
t or f, all HSV capsids are egressed to become infectious by envelope acquirement
false, there is the two proteins binding the HSV capsid upon initial export have a “quality control” mechanism that will not allow non-functional (No DNA) capsids to pass
explain the characteristics of poxviruses.
- large viruses
- DNA genome
- has envelope with many glycoproteins
- replicate in the cytoplasm!
- some are restricted to one host, others have multiple hosts
what is a zoonotic virus?
a virus that can jump hosts, often animal to human
t or f, disease is never seen in zoonotic hosts
false, disease is not normally seen in natural hosts but often seen in zoonotic hosts
explain
monkeypox
monkey pox is poxvirus that becomes fatal for humans. Once infected, monkey pox can be spread further by human - human transmission. small pox vaccine provides some immunity to it.
what is a dead end host?
once in the host the virus can no longer be transmitted. This is not the case for monkey pox
why do poxviruses have many enzymes within their core?
since they replicate in the cytoplasm they need defensive enzymes! additionally it cannot use the cells transcription machinery and needs to bring its own.
t or f, pox virus gene expression is sequential
true, similar to herpes virus
t or f, the initial proteins made by pox virus can be immunosupressents that may have a medial application
true
explain pox virus DNA replication
8
- dsDNA is linear and ends are closed
- so nuclease nicks one end exposing it.
- the ends are IR’s therefore they fold over and hybridize each other
- the 3’ end is now folded over and looks ds which acts as a primer for synthesis.
- DNA synthesis occurs at both ends of the linear genome making two genomes joined end to end
- the process begins again to form a concatemer
- this is cleaved into individual genomes
- the ends are sealed off.
