C) sense of taste
D) sense of touch
Human immunodeficiency virus (HIV) infects cells that have both CD4 and CCR5 cell
surface molecules. The viral nucleic acid molecules are enclosed in a protein capsid,
and the protein capsid is itself contained inside an envelope consisting of a lipid bilayer
membrane and viral glycoproteins. One hypothesis for viral entry into cells is that
binding of HIV membrane glycoproteins to CD4 and CCR5 initiates fusion of the HIV
membrane with the plasma membrane, releasing the viral capsid into the cytoplasm. An
alternative hypothesis is that HIV gains entry into the cell via receptor-mediated
endocytosis, and membrane fusion occurs in the endocytotic vesicle. To test these
alternative hypotheses for HIV entry, researchers labeled the lipids on the HIV
membrane with a red fluorescent dye.
In an HIV-infected cell producing HIV virus particles, the viral glycoprotein is
expressed on the plasma membrane. How do the viral glycoproteins get to the plasma
membrane? They are synthesized _____.
A) on ribosomes on the plasma membrane
B) by ribosomes in the rough ER and arrive at the plasma membrane in the membrane
of secretory vesicles
C) on free cytoplasmic ribosomes and then inserted into the plasma membrane
D) by ribosomes in the rough ER, secreted from the cell, and inserted into the plasma
membrane from the outside