Deck 7: Membranes: Their Structure,function,and Chemistry

Question 1

In response to temperature changes,cell membranes change state to become more solid or more fluid by undergoing

A)lipid raft formation.
B)membrane folding.
C)a phase transition.
D)transverse diffusion.
E)differential scanning calorimetry.

Answer 1

C

Question 2

Each of the following is true about homeoviscous adaptation in membranes except

A)maintains membrane viscosity despite changes in environmental temperature.
B)may decrease the average length of membrane lipid fatty acid tails.
C)may increase the unsaturation of membrane lipid fatty acid tails.
D)occurs primarily in homeothermic (warm-blooded)organisms and only rarely in poikilothermic (cold-blooded)organisms.
E)may increase the proportion of cholesterol in animal cell membranes.

Answer 2

D

Question 3

Which of the following types of organisms contain sphingomyelin in cell membranes?

A)prokaryotes
B)algae
C)animals
D)yeast
E)plants

Answer 3

C

Question 4

Each of the following is a function of membranes except

A)defining cell and organelle boundaries.
B)sites for specific biochemical functions.
C)information storage.
D)regulation of transport.
E)cell-cell communication.

Question 5

Which of the following lipids would you expect to find associated with chloroplast membranes?

A)phosphatidylserine
B)glycosphingolipid
C)monogalactosyldiacylglycerol
D)galactocerebroside
E)hopanoids

Question 6

Which of the following would be the most thermodynamically unfavorable membrane lipid activity in a membrane?

A)lateral diffusion
B)transverse diffusion
C)association with a neighboring lipid
D)association with cholesterol
E)rotation

Question 7

When a mouse cell and a human cell with different cell-surface protein markers are fused using polyethylene glycol (PEG)and immediately placed at 0°C,what would you expect happens to the mouse and human marker proteins?

A)Both the mouse and human marker proteins will rapidly disperse evenly throughout the fused membrane.
B)Only the mouse cell marker proteins will disperse throughout the fused membrane; the human marker proteins will remain confined to the original human region of the fused membrane.
C)The mouse and human markers will migrate to opposite poles of the fused membrane.
D)The mouse and human markers will migrate little and remain confined to their original membrane regions.
E)Both mouse and human markers will be endocytosed by the fused cell and destroyed in the fused cell.

Question 8

The most prominent lipids in animal cell membranes are

A)phospholipids.
B)glycolipids.
C)cholesterol.
D)phytosterol.
E)cerebrosides.

Question 9

Using a laser beam to inactivate fluorescence dye molecules connected to proteins or lipids on a cell membrane is called

A)liposome formation.
B)electrophoresis.
C)photobleaching.
D)freeze-fracturing.
E)affinity labeling.

Question 10

Cholesterol

A)is found in abundance in prokaryotic cell membranes.
B)buffers membrane fluidity by increasing fluidity at low temperature and decreasing fluidity at high temperature.
C)increases permeability for Ca2⁺.
D)increases permeability for small polar molecules.
E)All of the above are correct.

Question 11

When examining an electron micrograph of cells obtained from a new deep-sea life-form,you notice that the plasma membranes appear as two dark lines separated by a lightly stained region.Which of the following investigator(s)used a similar observation as the basis for a model of membrane structure?

A)Robertson
B)Gorter and Grendel
C)Unwin and Henderson
D)Overton
E)Singer and Nicolson

Question 12

Each of the following is a model for membrane structure except

A)Overton lipid coat.
B)Langmuir monolayer.
C)Gorter and Grendel bilayer.
D)Singer and Nicholson fluid mosaic.
E)Watson and Crick double helix.

Question 13

Each of the following is typical characteristics of an integral membrane protein transmembrane segment except

A)α-helical structure.
B)20-30 amino acids long.
C)composed primarily of hydrophobic amino acids.
D)amphipathic.
E)All are characteristics of a typical transmembrane segment.

Question 14

Which of the following proposed the "sandwich" model of membranes,in which lipid bilayers are coated on both sides with thin sheets of proteins?

A)Overton
B)Langmuir
C)Gorter and Grendel
D)Davson and Danielli
E)Robertson

Question 15

The composition of lipids in the outer and inner monolayers of cell membrane lipid bilayers is

A)asymmetrical; i.e.,different in each monolayer.
B)identical in each monolayer.
C)twice as concentrated in the inner monolayer as in the outer monolayer.
D)highly random for each monolayer.
E)the same for all cell plasma membranes but different from the composition in mitochondrial and chloroplast membranes.

Question 16

Which of the following would you expect to find predominating in the plasma membrane of a unicellular eukaryotic organism thriving in glacier ice?

A)20 carbon long saturated fatty acids.
B)18 carbon long saturated fatty acids.
C)20 carbon long fatty acids with 1 double bond.
D)18 carbon long fatty acids with 1 double bond.
E)16 carbon long fatty acids with 3 double bonds

Question 17

Of the following molecules,which would you predict diffuses most readily across membranes?

A)water
B)glucose
C)oxygen
D)serine
E)hydrogen ions

Question 18

Which of the following molecules enters kidney cells via a specific transporter?

A)water
B)carbon dioxide gas
C)cholesterol
D)ethanol
E)oxygen

Question 19

Each of the following is a type of cell-cell junctions except

A)adhesive.
B)tight.
C)gap.
D)plasmodesmata.
E)All are cell-cell junctions.

Question 20

Which of the following lipids is found concentrated in lipid rafts in animal cell plasma membranes?

A)cholesterol
B)phosphatidylcholine
C)phosphatidylserine
D)phophatidylethanolamine
E)phosphatidylinositol

Question 21

Localized regions of plasma membranes that contain cholesterol and proteins involved in cell signaling are known as

A)gap junctions.
B)arterial plaques.
C)cadherin junctions.
D)lipid rafts.
E)plasmodesmata.

Question 22

Which of the following would best be used to determine the lipid content of an isolated membrane fraction?

A)freeze-fracture analysis
B)thin-layer chromatography
C)SDS-PAGE
D)ferretin-linked antibodies
E)Western blot analysis

Question 23

Which of the following is true about glycosylated plasma membrane proteins?

A)Carbohydrate is added only after the protein is in the plasma membrane.
B)The carbohydrate usually is one sugar and rarely more than 5 sugars long.
C)Only one specific site is glycosylated on each protein.
D)N-linked carbohydrates are linked to hydroxyl groups in protein R groups.
E)The carbohydrates can be detected experimentally with ferretin-linked lectins.

Question 24

Which of the following types of protein would be most easily removed from a membrane by changing pH or ionic strength?

A)GPI-anchored protein
B)fatty acid-anchored protein
C)integral protein
D)peripheral protein
E)glycosylated integral protein

Question 25

Predict which of the following lipid characteristics would be most important to form the best liposomes for delivering a drug into a cell.

A)It contains a carbon ring structure similar to that in cholesterol.
B)It is linked to mannose
C)It is short and polar like glycerol.
D)It is amphipathic.
E)It has three fatty acid chains like a triglyceride.

Question 26

E.coli uses which of the following enzymes to regulate membrane fluidity?

A)glucose-6-phosphatase
B)desaturase
C)fatty acid convertase
D)gangliosidase
E)kinase

Question 27

Cell-cell communication in plants takes place via specialized structures called

A)plasmodesmata.
B)chloroplast outer membrane pores.
C)gap junctions.
D)lipid rafts.
E)connexons.

Question 28

The number and location of transmembrane segments in an integral membrane protein can be inferred from the amino acid sequence of the protein by a computer-generated

A)Western blot.
B)DNA sequence.
C)freeze-fracture replica.
D)hydropathy plot.
E)prediction of glycosylation sites.

Question 29

The most common number of carbons in fatty acid hydrocarbon chains of membrane phospholipids is

A)7.
B)10.
C)16.
D)19.
E)24.

Question 30

Lipid rafts are associated with which of the following activities?

A)responding to extracellular signals
B)transport of nutrients across cell membranes
C)immune responses
D)transport of cholera toxin into cells
E)All of the above are correct.

Question 31

Which of the following diseases results from impaired glycosphingolipid degradation?

A)heart disease
B)glycosphingolipid anemia
C)metabolic syndrome
D)erythrocyte spherocytosis
E)Tay-Sachs disease

Question 32

Naturally occurring unsaturated fatty acids typically

A)are highly branched.
B)are omega-3 fatty acids.
C)contain double bonds primarily in the trans configuration.
D)contain double bonds primarily in the cis configuration.
E)contain an odd number of carbon atoms.

Question 33

A colleague gives you two tubes containing membrane fractions from an animal cell lysate.One tube contains the plasma membrane fraction,and the other tube contains the mitochondrial inner membrane fraction,but the tubes are not labeled.When you analyze the macromolecule composition of the samples,you are confident that the second tube contains the mitochondrial fraction,because the sample has

A)a higher ratio of cholesterol to phospholipids.
B)a higher protein to lipid ratio.
C)a lower protein to lipid ratio.
D)more carbohydrate in glycoproteins.
E)more GPI-anchored proteins.

Question 34

Starting with shredded spinach leaves,you follow a procedure that separates cellular organelles into different fractions.To identify the fraction that contains the mitochondria,you should test for the presence of

A)aquaporin.
B)insulin receptors.
C)phospholipids present only in the mitochondrial outer membrane.
D)mitochondrial wall polysaccharides.
E)electron transport proteins.

Question 35

Which of the following would best detect a specific carbohydrate sugar on a glycoprotein?

A)thin-layer chromatography
B)freeze-fracture microscopy
C)photobleaching
D)ferritin-conjugated lectins
E)SDS-PAGE

Question 36

Hopanoids are

A)found exclusively in yeast.
B)related to cholesterol.
C)a type of glycolipid.
D)a type of phospholipid.
E)All of the above are correct.

Question 37

Which of the following is a sterol-like lipid associated with plant cell membranes?

A)stearate
B)phytosterol
C)linoleate
D)palmitate
E)hopanoids

Question 38

The technique that separates denatured proteins based on size is

A)SDS-PAGE.
B)FRAP.
C)thin-layer chromatography.
D)Western blotting.
E)freeze-fracture microscopy.

Question 39

Each of the following contributes to the system providing structural support to the erythrocyte plasma membrane except

A)the peripheral protein spectrin.
B)the integral protein glycophorin.
C)the peripheral protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH).
D)the peripheral protein ankyrin.
E)short actin filaments.

Question 40

FRAP has revealed that some proteins move in cell membranes much slower than they move in reconstituted liposomes.Which of the following could account for limited mobility of proteins in cell plasma membranes?

A)association with other proteins in a large complex.
B)association with lipid rafts.
C)anchorage to the extracellular matrix.
D)anchorage to the cell cytoskeleton.
E)All could limit protein mobility.

Question 41

________ is a sterol associated with fungal cell membranes.

Question 42

The structures of porin proteins in bacterial membranes and mitochondrial and chloroplast outer membranes is atypical for multipass integral proteins,because the porin transmembrane region is composed of a ________ instead of ________ transmembrane segments as in bacteriorhodopsin.

Question 43

The presence of trans fats in membranes ________ (increases or decreases)membrane fluidity and ________ (increases or decreases)the membrane transition temperature.

Question 44

The technique of transferring proteins from SDS-PAGE gels onto a membrane and using labeled antibodies to identify particular proteins is known as ________.

Question 45

The E.coli enzyme responsible for creating unsaturated bonds from saturated bonds in the cell membrane fatty acids at a lower environmental temperature is ________.

Question 46

Substances that can readily pass through the cell membrane are chemically ________ in nature.

Question 47

You are a microbiologist working with a new species of bacteria thriving in soil at 15°C.In the lab,you find this bacterium adjusts well to growth at 37°C.If this bacterium were "typical," what changes would you expect to find in the fatty acid composition of the membrane as the bacteria undergo homeoviscous adaption?

Question 48

________ organisms are unable to regulate their body temperature and must rely on ________ to maintain optimal membrane fluidity.

Question 49

The ability of some organisms to alter their membrane lipid composition in response to changes in temperature is known as ________.

Question 50

The current understanding of cell membrane structure is based on the ________ model.

Question 51

Individuals with the O blood group are known as universal donors because the Gal and GlcNAc groups that are recognized by the antibodies in A,B,and AB in other individuals are missing.Which of which of the following types of erythrocyte plasma membrane components lacks these GlcNAc groups?

A)a glycoprotein
B)a glycolipid
C)glycophorin
D)a GPI-anchored protein
E)a glycocalyx protein

Question 52

Amphipathic cationic antimicrobial peptides (AMPs)have potential as novel therapeutic agents in the treatment of skin bacterial diseases such as leprosy (caused by Mycobacterium leprae).Describe the nature of AMPs,where they can be found in nature,the mechanism by which amphipathic cationic AMPs kill bacteria,and how such AMPS could be developed into a treatment for leprosy.

Question 53

Using a radioactive molecule to identify which membrane proteins bind the molecule is called ________.

Question 54

The shift in membrane fluidity from a gel-like state to a more liquid state as temperature rises is known as a ________.

Question 55

You are interested in the mobility of two different unknown integral plasma membrane proteins-protein X and protein Y-in a cell.In one cell,you fluorescently label all the X proteins.In another cell,you label all the Y proteins.When you perform FRAP analysis on both cells,you find that most of the protein X fluorescence has recovered within 3 minutes,but recovery of the protein Y fluorescence is significantly slower.Even after 10 minutes,only 50% of the protein Y fluorescence has recovered.Describe the FRAP experimental protocol,explain what the results tell you about mobility of the X and Y proteins,and propose a possible explanation for why the mobilities of the two proteins differ.

Question 56

Most carbon double bonds in naturally occurring unsaturated fatty acids are in the ________ configuration,but some are in the ________ configuration,making the shape and packing of those fatty acids more like that of saturated fatty acids.

Question 57

Membrane lipids can be separated by ________,based on their ________.

Question 58

________ are small peptide molecules (10-50 amino acids in length)that can disrupt membrane structure.

Question 59

Hydropathy analysis of a membrane protein's amino acid sequence predicts the protein's transmembrane segments and orientation in the membrane.It is necessary to confirm those predictions with experimental analysis.One experimental approach for plasma membrane proteins is to use the protease trypsin to digest extracellular domains of these proteins.(Trypsin is hydrophilic and cannot cross the plasma membrane to enter the cell.)When added to cells,trypsin digests the hydrophilic portions of plasma membrane proteins exposed outside the cell into small fragments but will not have access to transmembrane or cytosolic regions of proteins.Design a general experiment using trypsin and SDS-PAGE to address membrane protein association and orientation,and describe specific expected results that would be consistent with the following predicted membrane protein associations and orientations:
a.a singlepass integral membrane protein with only its N-terminus exposed on the extracellular surface
b.a singlepass integral membrane protein with only its C-terminus exposed on the extracellular surface
c.a multipass integral membrane protein with only three hydrophilic loops exposed on the extracellular surface
d.a fatty acylated protein
e.a GPI-anchored protein

Question 60

Transmembrane proteins involved in detecting external chemical signals and relaying that information to the cell are known as ________ proteins.

Question 61

Recently,consumption of trans fatty acids has been linked to high blood cholesterol levels and increased risk of heart disease.The food industry has responded by decreasing use of "trans fats." Consider the following questions:
(a)How do the structures and transition temperatures of trans,cis,and saturated fatty acids differ,and what are the effects on membrane fluidity?
(b)Are trans fatty acids abundant in nature?
(c)The major source of trans fats is hydrogenated oils.(The trans fats are produced by a side reaction during the hydrogenation process.)Why has the food industry used synthetically produced hydrogenated oils?