Ch 11 Q - Membrane Structure

9) PART 1: Carbohydrates on the surface of leukocytes play an important role in responding to infection or inflammation. Place the following steps of the response in the correct order.

1.) cytokines are released at sites of infection or inflammatino and stimulate endothelial cells of blood vessels 2.) endothelial cells express selectins on their plasma membrane 3.) selectins bind to carbohydrates on the surface of leukocytes, causing them to stick 4.) leukocytes roll along vessel walls 5.) leukocytes crawl out of vessel into adjacent tissue

Detergent molecules are ___________ in nature and bind with membrane proteins and membrane lipids to disrupt their interactions and release the proteins from the membrane. Choose one: A. amphipahtic B. hydrophobic C. polar D. hydrophilic

A. amphipahtic

Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. When animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. The presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell. How might a cell actively engineer this phospholipid redistribution? Choose one: A. by activating a scramblase and inactivating a flippase in the plasma membrane B. by inverting the existing plasma membrane C. by inactivating a scramblase in the plasma membrane D. by inactivating both a flippase and a scramblase in the plasma membrane E. by boosting the activity of a flippase in the plasma membrane

A. by activating a scramblase and inactivating a flippase in the plasma membrane

Proteins that are associated with the membrane by noncovalent interactions with other membrane proteins are called ___________ proteins. Choose one: A. peripheral membrane B. integral membrane C. lipid-linked D. monolayer-associated

A. peripheral membrane

Why must all living cells carefully regulate the fluidity of their membranes? Choose one or more: A. to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell B. to allow cells to function at a broad range of temperatures C. to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides D. to allow membranes, under appropriate conditions, to fuse with one another and mix their molecules E. to constrain and confine the movement of proteins within the membrane bilayer

A. to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell C. to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides D. to allow membranes, under appropriate conditions, to fuse with one another and mix their molecules

9)PART 3: The following graphs show the number of adherent leukocytes found on the blood vessel wall in control conditions and after adding a selectin inhibitor, which blocks the function of selectin. Which of the following graphs correctly shows the effect of a selectin inhibitor on adherence of leukocytes to the vessel wall? Choose one: A. Graph A B. Graph B C. Graph C D. Cannot be determined from this experiment.

B. Graph B

When scientists were first studying the fluidity of membranes, they did an experiment using hybrid cells. Certain membrane proteins in a human cell and a mouse cell were labeled using antibodies coupled with differently colored fluorescent tags. The two cells were then coaxed into fusing, resulting in the formation of a single, double-sized hybrid cell. Using fluorescence microscopy, the scientists then tracked the distribution of the labeled proteins in the hybrid cell. Which best describes the results they saw and what they ultimately concluded? Choose one: A. At first, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became divided such that half faced the cytosol and half faced the hybrid cell exterior. This suggests that flippases are activated by cell fusion. B. Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became evenly intermixed over the entire cell surface. This suggests that proteins, like lipids, can move freely within the plane of the bilayer. C. The mouse and human proteins remained confined to the portion of the plasma membrane that derived from their original cell type. This suggests that cells can restrict the movement of their membrane proteins to establish cell-specific functional domains. D. The mouse and human proteins began to intermix and spread across the surface of the hybrid cell, but over time, one set of proteins became dominant and the other set was lost. This suggests that cells can ingest and destroy foreign proteins. E. Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins recombined such that they all fluoresced with a single, intermediate color. F. Initially, the mouse and human proteins intermixed, but over time, they were able to resegregate into distinct membrane domains. This suggests that cells can restrict the movement of membrane proteins.

B. Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became evenly intermixed over the entire cell surface. This suggests that proteins, like lipids, can move freely within the plane of the bilayer.

A cell membrane made up primarily of lipids with which characteristics would be the least fluid (i.e., most stiff)? Choose one: A. long, unsaturated fatty acid tails B. long, saturated fatty acid tails C. short, unsaturated fatty acid tails D. short, saturated fatty acid tails

B. long, saturated fatty acid tails

Which is a mechanism for restricting the movement of proteins in the plasma membrane? Choose one or more: A.forming a covalent linkage with membrane lipids B.tethering proteins to the extracellular matrix C.coating proteins with carbohydrates D.tethering proteins to the surface of another cell E.using barriers such as tight junctions F.tethering proteins to the cell cortex

B.tethering proteins to the extracellular matrix D.tethering proteins to the surface of another cell E.using barriers such as tight junctions F.tethering proteins to the cell cortex

9) PART 2: Mutation in the hemoglobin gene can cause sickle-cell anemia. The defective protein found in sickle-cell anemia causes red blood cells to "sickle"—become a misshapen C shape. These misshapen cells abnormally stick to each other and can become trapped by leukocytes (white blood cells) that are rolling or paused on the endothelial cells lining the vessel. This causes blockages of small blood vessels, causing severe pain and strokes called vaso-occlusive crisis. A new drug that binds and blocks selectin proteins is in phase III clinical trials to test for improvement in patients' symptoms. Why might this be an effective treatment for vaso-occlusive crisis? Choose one: A. Blocking selectins would block the ability of selectin to bind carbohydrates on the surface of red blood cells, preventing the blockage. B. Blocking selectins on red blood cells would prevent the red blood cells from binding to the blood vessel endothelial cells, preventing the blockage of red blood cells. C. Blocking selectins would block the ability of selectin to bind leukocytes, so leukocytes would be less likely to move slowly along the vessel wall and cause a blockage of red blood cells. D. Blocking selectins would reduce activation of pain sensors in the blood vessels.

C. Blocking selectins would block the ability of selectin to bind leukocytes, so leukocytes would be less likely to move slowly along the vessel wall and cause a blockage of red blood cells.

To study the structure of a particular membrane protein, the target protein is usually removed from the membrane and separated from other membrane proteins. Shown below are three different proteins associated with the cell membrane. Treatment with high salt would release which protein or proteins from the bilayer?

C. Gray membrane bound portion with green protein.

Which membrane would show a more rapid recovery of fluorescence in a FRAP study? Choose one: A. a membrane containing equal amounts of saturated and unsaturated fatty acids B. a membrane containing a larger proportion of saturated fatty acids C. a membrane containing a larger proportion of unsaturated fatty acids D. The saturation of fatty acids in a cell membrane does not affect the speed of fluorescence recovery in a FRAP study. E. a membrane containing a large amount of cholesterol

C. a membrane containing a larger proportion of unsaturated fatty acids

Phospholipids assemble into in a membrane using Choose one: A. assembly proteins. B. covalent bonds. C. hydrophobic forces. D. enzymes.

C. hydrophobic forces.

Bacteriorhodopsin is a membrane transport protein that uses sunlight to do what? Choose one: A. pump photons into the cell to generate a deep purple color B. convert CO2 into sugar during photosynthesis in archaea that live in salt marshes C. pump protons out of the cell to generate a proton gradient across the plasma membrane D. hydrolyze ATP molecules to allow salt-dwelling, anaerobic archaea to produce energy

C. pump protons out of the cell to generate a proton gradient across the plasma membrane

Fluorescence recovery after photobleaching (FRAP) is used to monitor the movement of fluorescently labeled molecules within the plane of a cell membrane. The molecules labeled are often proteins, but lipids can be labeled too.How would the curve that represents FRAP for labeled proteins compare to the curve representing labeled lipids? Choose one: A. The FRAP curve for proteins would show a much more rapid recovery but only reach about 50% of the initial levels of fluorescence. B. The FRAP curve for proteins would show a much more rapid recovery to initial levels of fluorescence. C. The curves would be identical. D. The FRAP curve for lipids would show a much more rapid recovery to initial levels of fluorescence. E. The FRAP curve for lipids would show a much more rapid recovery but only reach about 50% of the initial levels of fluorescence.

D. The FRAP curve for lipids would show a much more rapid recovery to initial levels of fluorescence.

When the transport vesicle shown below fuses with the plasma membrane, which monolayer will face the cell cytosol? Choose one: A. It depends on the cargo the vesicle is carrying. B. It depends on whether the vesicle is coming from the endoplasmic reticulum or the Golgi apparatus. C. Half the time the orange monolayer will face the cytosol, and half the time the blue monolayer will face the cytosol. D. The orange monolayer will face the cytosol. E. The blue monolayer will face the cytosol.

D. The orange monolayer will face the cytosol.

In an electron transport chain, electrons are passed from one transmembrane electron carrier to another, driving proton movement across a membrane (see image below). The protons then flow through ATP synthase (not shown) to generate ATP. In a 2018 article (Budin, et al., Science vol. 362) researchers probed how membrane fluidity affects electron transport chain activity and ATP production in E. coli by manipulating membrane fluidity and measuring respiration. How could researchers have increased membrane fluidity? Choose one: A. increase the length of the fatty acid tails in phospholipids B. decrease the temperature of the media the E. coli were grown in C. increase the amount of cholesterol present in the bacterial membranes D. increase the proportion of phospholipids with unsaturated fatty acids

D. increase the proportion of phospholipids with unsaturated fatty acids

Organisms that live in cold climates adapt to low temperatures by doing which of the following? Choose one: A. increasing the amounts of saturated fatty acids in their membranes to help keep their membranes fluid B. increasing the amounts of unsaturated fatty acids in their membranes to help decrease the fluidity of their membranes C. decreasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid D. increasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid E. increasing the amounts of saturated fatty acids in their membranes to help decrease the fluidity of their membranes

D. increasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid

In a patch of animal cell membrane about 10 μm in area, which will be true? Choose one: A. There will be about an equal number of proteins and lipids. B. Because the lipid bilayer acts as a two-dimensional fluid, there is no way to predict the relative numbers of proteins and lipids in any patch of cell membrane. C. There will be more carbohydrates than lipids. D. There will be more proteins than lipids. E. There will be more lipids than proteins.

E. There will be more lipids than proteins.

What type of protein moves randomly selected phospholipids from one monolayer of a lipid bilayer to the other? Choose one: A. none; such movement occurs spontaneously and relatively quickly B. flippase C. phospholipase D. none; phospholipids cannot move from one monolayer to another E. scramblase

E. scramblase