Exam 7: Membrane Structure and Function

Use the paragraph and accompanying figure to answer the following questions. 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 ________.

The difference between pinocytosis and receptor-mediated endocytosis is that ________.

Five dialysis bags, constructed of a type of membrane that is permeable to water and 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 with the highest initial concentration of sucrose?

Which of the following types of molecules lack hydrophilic domains?

Which of the following statements is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?

When a cell is in equilibrium with its environment, which of the following processes occurs for substances that can diffuse through the plasma membrane?

A sodium-potassium pump ________.

When a plant cell, such as one from a tulip leaf, is submerged in a hypertonic solution, what is likely to occur?

In which of the following environments would there be the greatest need for osmoregulation?

For the following questions, match the labeled component of the cell membrane in the figure with its description. - Which component in the accompanying figure is hydrophilic?

Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water ________.

An organism with a cell wall would most likely be unable to take in materials through ________.

An animal cell lacking carbohydrates on the external surface of its plasma membrane would likely be impaired in which function?

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 (NaCl), 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. At the beginning of the U-tube experiment illustrated above, which of the following statements is true?

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

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

What will happen to a red blood cell (RBC), which has an internal ion content of about 0.9%, if it is placed into a beaker of pure water?

What kinds of molecules pass through a cell membrane most easily?

Three lab groups carried out an experiment to identify the concentration of sucrose in six solutions. Each unknown contained one of the following sucrose concentrations: 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M. Cubes of sweet potato (1 cm³)were soaked for 24 hours in each solution and weighed to determine the change in mass. Each data entry represents the average of three sample replicates expressed as percent change in mass following a 24-hour soak in the unknown solutions. Unknown Percent change in Percent change in Percent change in Graup 1 Guss mass A 6.6 7.8 Group 3 B 3.1 3.7 7.5 E -2.7 -3.5 2.9 D 0.7 0.5 -2.5 E -11.6 -12.3 1.1 F -5.2 6.2 -12.6 Based on the data provided, the intracellular molarity of dissolved solutes in sweet potato cells is approximately ________.

According to the fluid mosaic model of cell membranes, phospholipids ________.