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Exam 11: Membrane Structure

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Question 21

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Membrane lipids are capable of many different types of movement.Which of these does not occur spontaneously in biological membranes?

A) moving between lipid layers
B) lateral movement
C) rotation around the long axis of a fatty acid
D) flexing of hydrocarbon chains

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Question 22

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Which of the following statements is TRUE?

A) Phospholipids will spontaneously form liposomes in nonpolar solvents.
B) In eukaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer.
C) Membrane lipids diffuse within the plane of the membrane.
D) Membrane lipids frequently flip-flop between one monolayer and the other.

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Question 23

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We can estimate the relative mobility of a population of molecules along the surface of a living cell by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as molecules migrate back into the bleached area.What is this method called? What does the abbreviation stand for?

A bacterium is suddenly expelled from a warm human intestine into the cold world outside.Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity?

Membrane proteins, like membrane lipids, can move laterally by exchanging positions with other membrane components.Which type of membrane protein is expected to be the least mobile, based on their function?

You have isolated two mutants of a normally pear-shaped microorganism that have lost their distinctive shape and are now round.One of the mutants has a defect in a protein that you call A and the other has a defect in a protein that you call B.First, you grind up each type of mutant cell and normal cells separately and separate the plasma membranes from the cytoplasm, forming the first cell extract.Then you set aside a portion of each fraction for later testing.Next, you wash the remaining portion of the membrane fractions with a low concentration of urea (which will unfold proteins and disrupt their ability to interact with other proteins) and centrifuge the mixture.The membranes and their constituent proteins form a pellet, and the proteins liberated from the membranes by the urea wash remain in the supernatant.When you check each of the fractions for the presence of A or B, you obtain the results given below. $\quad\quad\quad\quad\quad\quad\quad\text { First cell extract }$$\quad\quad\quad\quad\quad\text { After urea wash and centrifugation }$ $\begin{array}{lcccc}\hline&\text { Membrane }&\text { Cytosol }&\quad\quad\text {Membrane }&\text {Supernatant }\\\hline\text { Normal cells } & \text { A and B } & \text { no A or B } & \text { A } & \text { B } \\\hline \text { Mutant A } & \text { A } & \text { B } & \text { A } & \text { no A or B } \\\hline \text { Mutant B } & \text { A } & \text { B } & \text { A } & \text { no A or B }\end{array}$ Figure 11-15 Use these initial observations to classify membrane proteins A and B.What additional information can be inferred from this data set that helps you understand the mutant phenotype?

Membrane curvature is influenced by the differential lipid composition of the two membrane monolayers.Which factor do you think has the largest impact on the curvature of biological membranes?

Which mechanism best describes the process by which a budding yeast cell designates the site of new bud formation during cell division?

Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other.Which group of enzymes accomplishes both of these tasks?

It is possible to follow the movement of a single molecule or a small group of molecules.This requires the use of antibodies linked to small particles of gold, which appear as dark spots when tracked through video microscopy.What is this method called? What does the abbreviation stand for?

Anemia, a condition that results in individuals with a low red blood cell count, can be caused by a number of factors.Why do individuals with defects in the spectrin protein often have this condition?

Indicate whether the following statements are TRUE or FALSE.If a statement is false, explain why it is false.

Which of the following functions of the plasma membrane is possible without membrane proteins?

Which mechanism best describes the process by which an antigen-presenting cell triggers an adaptive immune response?

Indicate whether the following statements are TRUE or FALSE.If a statement is false, explain why it is false.

Red blood cells have been very useful in the study of membranes and the protein components that provide structural support.Which of the following proteins is the principal fibrous protein in the cortex of the red blood cell?

The endothelial cells found closest to the site of an infection express proteins called lectins.Each lectin binds to a particular __________ that is presented on the surface of a target cell.

Some lipases are able to cleave the covalent bonds between the glycerol backbone and the attached fatty acid.What final products do you expect to accumulate through the action of the enzyme monoacylglycerol lipase?

Which type of lipids are the most abundant in the plasma membrane?

Three different membrane components are shown in Figure 11-16.Using the list below, identify the three components, and label the chemical groups indicated. A.glycerol B.sugar C.phospholipid D.glycolipid E.sterol F.unsaturated hydrocarbon G.saturated hydrocarbon H.sterol polar head group Figure 11-16