HIV viral nucleic acid molecules are enclosed in a protein
capsid, which is itself contained inside a lipid envelope.
One hypothesis for viral entry into cells is that the virus
binds to proteins on the surface of a cell and fuses with the
plasma membrane, releasing the viral capsid into the
cytoplasm. An alternative hypothesis is that HIV is
brought into the cell via receptor-mediated endocytosis,
and membrane fusion occurs in the endocytotic vesicle. To
test these two hypotheses, researchers labeled the lipids on
the HIV membrane with a red ﬂuorescent dye.
20) What would you see if you could follow the
location of the dye by live-cell ﬂuorescence
microscopy if HIV is endocytosed ﬁrst, and
then fuses with the endocytotic vesicle
A) A spot of red ﬂuorescence will remain
on the infected cell's plasma
membrane, marking the site of
membrane fusion and HIV entry.
B) Red ﬂuorescence will move into the
cytoplasm as well as remain in the cell
membrane after delivering the capsid.
C) The dye-labeled lipids will diffuse in
the endocytotic vesicle membrane and
become difﬁcult to detect.
D) A spot of red ﬂuorescence will move
into the infected cell's interior.