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Exam 7: Membrane Structure and Function

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Question 21

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When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are

A) peripheral proteins.
B) phospholipids.
C) carbohydrates.
D) integral proteins.
E) cholesterol molecules.

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Question 22

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Use the following information to answer the questions below. Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes. -If the sodium ion concentration outside the cell increases, and the CFTR channel is open, in what direction will chloride ions and water move across the cell membrane?

A) Chloride ions will move out of the cell, and water will move into the cell.
B) Both chloride ions and water will move out of the cell.
C) Chloride ions will move into the cell, and water will move out of the cell.
D) Both chloride ions and water will move into the cell.
E) The movement of chloride ions and water molecules will not be affected by changes in sodium ion concentration outside the cell.

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Question 23

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Use the following information to answer the questions below. Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes. -The CFTR protein belongs to what category of membrane proteins?

Which of the following is true of integral membrane proteins?

In a Paramecium, cell surface integral membrane proteins are synthesized

For the following questions, match the labelled component of the cell membrane in the figure with its description. -After the system reaches equilibrium, what changes are observed?

Use the following information to answer the questions below. Five dialysis bags, constructed from a semipermeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed. -Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?

The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?

In order for a protein to be an integral membrane protein, it would have to be

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly

The formulation of a model for a structure or for a process serves which of the following purposes?

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

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. -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-labelled HIV was added to the cells. What is the best conclusion from these observations?

Which of the following membrane activities require energy from ATP hydrolysis?

In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model?

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. -If HIV first enters the cell in an endocytotic vesicle, instead of directly fusing with the plasma membrane, then

The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?

For the following questions, match the labelled component of the cell membrane in the figure with its description. -Which component is a microfilament of the cytoskeleton?