Chapter 7 - Membrane Structure Flashcards
The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane; the membrane is permeable to sodium chloride but not to glucose; side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl0< and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride; initially, the volume in both arms is the same;
if you examine side A after three days, you should find
a decrease in the concentration of NaCl and a decrease in the water level
which of the following is a characteristic feature of a carrier protein in a plasma membrane?
it exhibits a specificity for a particular type of molecule
what is the voltage across a membrane called?
membrane potential
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;
using live-cell fluorescence microscopy, researchers observed that a red fluorescent spot moved from the plasma membrane into the interior of target cells when red fluorescent dye-labeled HIV was added to the cells; what is the best conclusion from these observations?
the hypothesis that HIV enters the cell via fusion with the target cell plasma membrane is not supported
the presence of cholesterol in the plasma membranes of some animals
enables the membrane to stay fluid more easily when cell temperature drops
what kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?
the animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution
which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
the double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly
which of the following would increase the electrochemical potential across a membrane?
a proton pump
