what is a virus?
obligate intracellular pathogens
can viruses replicate anywhere? Why?
no, they must replicate inside a host living cells, by using the host's cellular machinery to do transcription, translation and replication
what do viruses synthesize?
what do virions do?
they help in the transfer of the viral genome (RNA or DNA) to other living cells
what do viruses lack?
mitochondria, ribosomes, enzymes
true or false: viruses are bigger than bacteria and host cells
false, they are much more smaller
what are the 2 stages of a virus?
1) Virion = the infectious form
2) intracellular form (its genome alone) = non-infectious
what is the structural parts of a virus (after infection)?
which of these parts is optional?
1) Viral DNA/RNA
3) matrix tegument
the ENVELOPE is optional
what are the 3 forms that the nucleocapsid can have?
how do we find the viral envelope? (how does it look or what is it?)
its the host cell lipid bilayer, with viral glycolipids in the surface
how do you know if the virus is enveloped or naked?
enveloped = nucleocapsid + glycoproteins and the nuclear membrane
naked = only the nucleocapsid
what makes up the nucleocapsid?
2) structural protein
what determines what steps and enzymes are necessary to create the viral mRNA?
the type of nucleic acid
what enzyme is important for single stranded RNA retrovirus?
why is it very important to know what type of nucleic acid a virus is?
because by determining what type of nucleic acid the virus is, we can select the corret anti-biotic to treat it with
what type of nucleocapsid do all naked virus have?
what type of nucleocapsid do all enveloped viruses have?
what is the function of the outer structural proteins?
1) protect the genetic material
2) mediates the attachment of the virus to specific host cell receptors on the cell surface
3) activate the immune system to kill virus cell (activate neutralizing antibodies and CTL's)
when does a immune response occur? (after what 2 events?)
1) natural exposure
what determines the viral classification?
nucleic acid and the envelope
what viruses are less stable?
enveloped DNA/RNA viruses
how are enveloped DNA/RNA viruses transmitted?
through direct contact
(blood or bodily fluids)
what viruses are more stable and can survive a long time in the environment?
naked DNA/RNA viruses
how do naked viruses spread?
through indirect means (fecal-oral route)
what is an example of an enveloped DNA virus?
what is an example of a naked RNA virus?
What are the DNA viruses?
5) Herpes virus
what 2 viruses have polymerase?
All DNA viruses are icosahedral, except for?
all DNA viruses are what single straded or double stranded?
Who is the exception?
double stranded DNA
what is a double stranded RNA virus example?
what are the positive RNA viruses?
what is an example of a retrovirus?
what are the 6 types of negative RNA viruses?
what are the 5 steps of the viral cycle?
what is PFU?
is a plaque forming unit
once virus infects a single cell, spread and kill surrounding cells to cause a plaque (a clear area or dead cells) surrounded by live cells.
What is it called the time after the nucleic acid is released and before the virus starts replicating?
the time before full virions are released after infection is called?
the latent phase
what do virions have that allows them to restrict the host cell specificity (or tropism)?
VAP ( virion attachment protein)
what are the VAP of the HIV virus? to what do they attach to?
GP 120---binds to CCR5 on macrophages
GP140 ----binds to CD4
what cells does HIV infect?
what are the VAP of epstein-Bar virus? to what receptor do they bind? and on what cell?
CR2 and CD21
they bind to C3d complement receptor on B cells
to what does rhinovirus VAP bind to ? on what cells?
ICAM-1 on endothelial cells
what is the VAP of Influenza A virus? to what cells does it bind to?
sialic acid and binds to epithelial cells
where does penetration of a virus occur?
at the cell surface
where does uncoating occur in a virus?
once inside the cell
the process of uncoating is dependant on what?
it is pH dependant
in order for the virus to replicate, what must physically separate in the viral structure?
the capsid from the viral genome
uncoating depends on what in the host cell?
depends on cellular enzymes
if the virus loses this from its structure during uncoating will lead to loss of ability to infect other cells...
what mechanisms are used to facilitate nucleic acid release?
1) clathrin-dependent pathway
3) caveolar pathway
4) clathrin- and cavolin-independant pathway
the virion genome will encode this two types of genes:
what is the early gene made by the viral genome used for?
it is needed for replication
what is the late gene made from the viral genome used for?
it is required for packaging
what kind of proteins does the viral genome instruct the cell to produce?
structural and non-structural proteins
what are structural proteins?
are the late proteins found in virion particles
what are non-structural proteins?
early proteins produced in infected cells but not found in virions
what does the herpes virus have to do before it can integrate into the host genome?
it has to use reverse transcriptase to convert RNA --> DNA
what enzyme does the herpes virus use to integrate into the host genome?
what happens in the assembly phase of a virus?
viral proteins and copies of nucleic acid are assembled
how are the virions assembled during the assembly phase?
virions are formed by packaging the genomes with capsid proteins and if the virus is enveloped, by wrapping the nucleocapsid in an envelope
how are non-enveloped viruses released into the body once they get made in the infected cell?
when the cell dies, they get released
how are enveloped virions released into from the cell they got made?
where do enveloped viruses acquire their lipid membrane?
at the cellular plasma membrane or at the golgi by budding
what happens to the plasma membrane while the virus used budding?
virus takes a piece of the plasma membrane and pulling away a piece and eventually reducing the amount on the cell