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Exam 6: Lipids, membranes, and the First Cells

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Question 21

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What is the most important factor in explaining why osmosis occurs spontaneously?

A) It leads to an increase in entropy.
B) It leads to a decrease in entropy.
C) The process is exothermic.
D) The process is endothermic.

E) A) and B)
F) A) and C)

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Question 22

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Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes?

A) Cholesterol binds to the outside surface of a membrane,thus blocking the movement of solutes.
B) Because cholesterol is amphipathic,it forms tiny vesicles that trap solutes.
C) Because cholesterol is amphipathic,it fits in between the phospholipids and blocks diffusion through the membrane.
D) Cholesterol has four rings in its structure that can sequester (trap) solutes.

E) C) and D)
F) B) and D)

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Question 23

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You place yeast cells in a glucose solution and plot the rate of glucose uptake.You see an increase in glucose uptake over time (that is,the longer the yeast are in the sugar solution,the faster they can take sugar into the cell) .The most likely explanation for this is the cell membrane is becoming more permeable because _____.

Which of the following observations made with freeze-fracture electron microscopy provides evidence for the fluid-mosaic model of membrane structure?

Which of the following means of transport would most likely be used for moving a medium-sized molecule (like a monosaccharide or an amino acid) from a low concentration on the outside of a cell to a high concentration on the inside of a cell?

Use the following information when answering the corresponding question(s) . Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin A) .Opsin is a membrane protein with several α-helical segments that loop back and forth through the plasma membrane.There are two classes of rhodopsins.According to Oded Beje,one class has relatively slow dynamics (a photocycle of approximately 0.5 second) and is well suited for light detection.The second class has faster dynamics (a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis pumping of protons or chloride ions across cell membranes.Oded Beje was the first,in September 2000,to report on a rhodopsin (proteorhodopsin) found in the domain Bacteria.[Source: O.Beje et al. ,Science 289 (2000) : 1902.] -GLUT-1 is an example of what?

Which of the following is true of osmosis?

Use the following information when answering the corresponding question(s) . Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin A) .Opsin is a membrane protein with several α-helical segments that loop back and forth through the plasma membrane.There are two classes of rhodopsins.According to Oded Beje,one class has relatively slow dynamics (a photocycle of approximately 0.5 second) and is well suited for light detection.The second class has faster dynamics (a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis pumping of protons or chloride ions across cell membranes.Oded Beje was the first,in September 2000,to report on a rhodopsin (proteorhodopsin) found in the domain Bacteria.[Source: O.Beje et al. ,Science 289 (2000) : 1902.] -Refer to the paragraph on Rhodopsins.Which of the following best describes this particular protein?

You make a phospholipid bilayer with short,saturated hydrocarbon tails.You measure the permeability of this membrane to oxygen.You are going to change the length of the hydrocarbon tails and remeasure membrane permeability,but first your boss asks you to graph the data you expect if there is no effect of hydrocarbon tail length on membrane permeability (your null hypothesis) .Which of the graphs below best represents the data you expect if your null hypothesis is correct?

Which of the following crosses lipid bilayers the slowest?

Lipids that form membranes have what kind of structure?

Which of the following phospholipid membranes would be most permeable to glycerol?

The term phospholipid can best be described by which of the following?

Which of the following substances would most likely require a protein to facilitate its diffusion across a cell membrane?

Steroids such as cholesterol are an important component of animal cell membranes but do not actually form the membrane.Why?

Phospholipids can form all of the following structures in water except which one?

Which of the following crosses lipid bilayers the fastest?

Use the following information when answering the corresponding question(s) . Rhodopsins are light-sensitive molecules composed of a protein (opsin) and retinal (derivative of vitamin A) .Opsin is a membrane protein with several α-helical segments that loop back and forth through the plasma membrane.There are two classes of rhodopsins.According to Oded Beje,one class has relatively slow dynamics (a photocycle of approximately 0.5 second) and is well suited for light detection.The second class has faster dynamics (a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis pumping of protons or chloride ions across cell membranes.Oded Beje was the first,in September 2000,to report on a rhodopsin (proteorhodopsin) found in the domain Bacteria.[Source: O.Beje et al. ,Science 289 (2000) : 1902.] -Proteorhodopsin consists of a single polypeptide chain.What is the highest level of structure found in this protein?

Where would you most likely find an integral membrane protein?

You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids.After testing the permeability of this membrane to glucose,you increase the proportion of unsaturated phospholipids in the bilayer.What will happen to the membrane's permeability to glucose?