Exam 11: Membrane Structure

We know the detailed molecular structure and mechanism of action of the transmembrane protein bacteriorhodopsin.This protein uses sunlight as the source of energy to pump __________ out of the cell.

New membrane phospholipids are synthesized by enzymes bound to the __________ side of the __________ membrane.

Which mechanism best describes the process by which nutrients are taken up selectively at the apical surface of the epithelial cells that line the gut and released from their basal and lateral surfaces?

While many prokaryotic cells have a single membrane bilayer, all eukaryotic cells have a complex system of internal membrane-bound compartments.How might it be advantageous for the cell to have these additional compartments?

Which of the following is most likely to occur after the lipid bilayer is pierced?

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once. amphipathic hydrophilic noncovalently cortical hydrophobic peripheral covalently integral transmembrane detergent micelle unfolded There are several ways that membrane proteins can associate with the cell membrane.Membrane proteins that extend through the lipid bilayer are called __________ proteins and have __________ regions that are exposed to the interior of the bilayer.On the other hand, membrane-associated proteins do not span the bilayer and instead associate with the membrane through an α helix that is __________.Other proteins are __________ attached to lipid molecules that are inserted in the membrane.__________ membrane proteins are linked to the membrane through noncovalent interactions with other membrane-bound proteins.

The amino acid sequences below represent the sequences of transmembrane helices.The characteristics of α helices that form a channel are different from those that form a single transmembrane domain.Select the helix that forms a single transmembrane domain.

Diversity among the oligosaccharide chains found in the carbohydrate coating of the cell surface can be achieved in which of the following ways?

Three phospholipids, X, Y, and Z, are distributed in the plasma membrane as indicated in Figure 11-10.For which of these phospholipids does a flippase probably exist? Figure 11-10

Thermal motion promotes lateral position exchanges between lipid molecules within a monolayer.In an artificial bilayer, this movement has been estimated to be ~2 μm/second.This represents the entire length of a bacterial cell.Do you expect the lateral movement of a lipid molecule within a biological membrane to be equally fast? Explain your answer.

Explain the importance of glycolipids in the plasma membrane, identify where they are produced inside the cell, and describe the mechanism by which they are transported to the plasma membrane and presented to the extracellular environment.Draw a diagram to support your answer.

Even though proteins can form channels across biological membranes using either α helices or β sheets, channels made of α helices are more versatile.Explain the physical constraints on β-barrel structures and why these constraints do not apply to channels made of α helices.

Cholesterol serves several essential functions in mammalian cells.Which of the following is NOT influenced by cholesterol?

Porin proteins form large, barrel-like channels in the membrane.Which of the following statements about these channels is FALSE?

Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)?

Most animal fats form a solid at room temperature, while plant fats remain liquid at room temperature.Which of the following is a feature of lipids in plant membranes that best explains this difference?

Formation of a lipid bilayer is energetically favorable.How does this arrangement result in higher entropy for the system, and thus make bilayer formation energetically favorable?

Which mechanism best describes the process by which neutrophils are recruited by endothelial cells?

Consider the apical location of a particular protein expressed in epithelial cells, illustrated in part A of Figure 11-36.When a molecule that chelates calcium is added to the cell culture medium, you observe a redistribution of that protein around the entire cell, shown in part B of Figure 11-36.Which is most likely to be true about the role of calcium in maintaining an apical distribution of protein A? Figure 11-36

Which mechanism best describes the process by which focal adhesions are formed to promote cell motility?