Use the following information to answer the questions below.
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 labelled the lipids on the HIV membrane with a red fluorescent dye.

-What would be observed by live-cell fluorescence microscopy if HIV is endocytosed first, and then fuses with the endocytotic vesicle membrane?
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)The red fluorescent dye-labelled lipids will diffuse in the endocytotic vesicle membrane and become difficult to detect.
C)A spot of red fluorescence will move into the infected cell's interior.
D)A spot of red fluorescence will remain outside the cell after delivering the viral capsid.
E)Fluorescence microscopy does not have enough resolution to visualize fluorescently labelled HIV virus particles.

Question

Use the following information to answer the questions below.
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 labelled the lipids on the HIV membrane with a red fluorescent dye.
 
-What would be observed by live-cell fluorescence microscopy if HIV is endocytosed first, and then fuses with the endocytotic vesicle membrane?
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)The red fluorescent dye-labelled lipids will diffuse in the endocytotic vesicle membrane and become difficult to detect. 
C)A spot of red fluorescence will move into the infected cell's interior. 
D)A spot of red fluorescence will remain outside the cell after delivering the viral capsid. 
E)Fluorescence microscopy does not have enough resolution to visualize fluorescently labelled HIV virus particles.

Quizplus · Accepted Answer

If HIV gains entry into the cell via receptor-mediated endocytosis, the red fluorescence on the viral lipids would move into the infected cell's interior along with the endocytotic vesicle. Option A is incorrect because no membrane fusion occurs on the plasma membrane. Option B is incorrect because endocytotic vesicles have a distinct lipid composition and would not be expected to diffuse into the vesicle membrane. Option D is incorrect because the viral capsid would be released into the cytoplasm, not outside the cell. Option E is incorrect because live-cell fluorescence microscopy can visualize fluorescently labelled virus particles.

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