so this is HIV it's a typical retrovirus
meaning that it has an outer envelope
and in the center it has two copies of
RNA as well as an enzyme here in blue
that's reverse transcriptase which will
ultimately turn that RNA into DNA the
the virus itself with this outer
envelope protein actually directly
infects T helper cells the way that it
does this is that as it comes up to the
cell surface it uses receptors that are
on T helper cells and exclusive to T
helper cells which are cd4 molecule
which really defines T helper cells it's
a surface receptor that binds to the
envelope protein it that causes a
conformational change and allows a
second receptor to grab hold of the
envelope this is the key makind
co-receptor it's also called ccr5 and
we'll talk about that more what happens
now is that the the stalk of the
envelope protein pierces through the
from the virus into the into the host
cell and starts to draw the two cell
membrane the cell membrane in the viral
membrane together and what ultimately
happens is fusion of those two membranes
and the viral genetic material is
injected essentially into the cell and
the envelope protein is left at the cell
surface the virus has a matrix and a
capsid protein shown here in green and
red that that essentially are digested
when it enters into the cell that
releases viral enzymes in the viral RNA
and here we have reverse transcriptase
which takes the viral RNA and using host
nucleotides converts that viral RNA into
a single strand of DNA while it does
that it makes some random errors which
is characteristic of reverse
transcriptase it has very poor
proofreading activity
that single-stranded DNA now is again
reverse transcribed into a
double-stranded DNA
at that point another enzyme that has
come in with the virus in the beginning
called integrase essentially grabs hold
of that double-stranded DNA and carries
it through a nuclear pore into the
nucleus of the cell
within the nucleus of the cell it finds
the host chromosome and it basically the
integrase enzyme makes a nick in the
host DNA and allows for HIV to insert
itself into the host chromosome and that
right there is what establishes lifelong
infection
now RNA polymerase comes along and makes
messenger RNA
those messenger RNAs encode for
different viral proteins they end up
associating with ribosomes on at the
surface of the rough endoplasmic
reticulum and here's a piece of mRNA
that's making envelope protein which is
directly produced into the endoplasmic
reticulum and it's shuttled them through
the endoplasmic reticulum and taken to
the cell surface where at the cell
surface it becomes embedded in the
cellular membrane and at this point
coalescing with other envelope proteins
that have been produced you have this
cluster of envelope proteins now on the
surface of this infected cell at the
same time there are other messenger RNAs
that are being produced that allow for
translation of other viral proteins so
here are additional viral proteins being
made which are going to be used to make
up the key components that that the
virus ultimately is going to need these
are transported again to the cell
surface to the area where these envelope
proteins are and a strand of RNA as well
as a some of the enzymes are part of
that complex
this then buds off at the cell surface
at this point but it's still not a
mature virion because the poly protein
chain needs to still be digested into
its component parts that's done by an
enzyme called protease protease breaks
up those poly protein chains and
ultimately allows for them to coalesce
and form the mature structures that make
up the final virion and now you have a
mature infectious virion that can go on
now to infect other cells
once that happens now the cell can
produce tons of viruses and this is
really what then keeps the whole process
going