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

Question 1

With respect to the outer and inner faces of the lipid bilayer of the cell membrane,the composition of lipids is

A)asymmetrical.
B)identical.
C)not identical but symmetrical.
D)highly random and varies throughout the cell.
E)a mirror image.

Answer 1

A

Question 2

Of the following lipids,which would you expect to find associated with chloroplast membranes?

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

Answer 2

C

Question 3

Two cells with different cell-surface markers are fused in the presence of polyethylene glycol (PEG).The cells are then placed at 0°C.What do you expect to observe about the individual cell markers?

A)The markers will evenly disperse throughout both membranes.
B)Only one marker will disperse, while the other remains stationary.
C)Both sets of markers will not mix but will migrate to opposite poles from one another.
D)The markers will essentially remain where they are, with little migration.
E)The markers will be endocytosed by the fused cell and then redistributed as fused markers.

Answer 3

D

Question 4

Which of the following molecules would enter the cell via a specialized transmembrane receptor?

A)water
B)fatty acids
C)cholesterol
D)ethanol
E)gases

Question 5

Of the following lipids,which is found in approximately equal amounts in both the outer and inner portions of the lipid bilayer?

A)cholesterol
B)glycolipid
C)phosphatidylserine
D)phophatidylethanolamine
E)phophatidylinositol

Question 6

Which of the following is not a function of membranes?

A)define cell boundaries
B)compartmentalization
C)information storage
D)regulation of transport
E)cell-cell communication

Question 7

Cholesterol

A)is found in abundance in prokaryotic cell membranes.
B)intercalates between the fatty acid chains within the bilayer.
C)increases permeability for small cations.
D)destabilizes the cell membrane.
E)is found only in plants.

Question 8

Where would you expect to find an organism possessing a cell membrane composed of large proportions of cholesterol and a predominance of unsaturated fatty acids?

A)frozen wastelands
B)temperate regions
C)tropical regions
D)equatorial regions
E)upper levels of an aquatic environment

Question 9

The ability of some organisms to compensate for temperature changes by altering the lipid composition of membrane lipids is known as

A)homeoviscous adaptation.
B)ectothermic adaptation.
C)kleptothermic adaptation.
D)A and B only
E)none of the above

Question 10

With regard to the semipermeable nature of the plasma membrane,which of the following would readily cross without the aid of a transport protein?

A)calcium ions
B)glucose
C)water
D)amino acids
E)DNA

Question 11

Temperature has a dramatic effect upon cell membranes.This influence can readily make a cell membrane more solid or more fluid in response to the temperature.This is an example of

A)liquidation.
B)membrane flexibility.
C)phase transition.
D)membrane asymmetry.
E)scanning calorimetry.

Question 12

Which of the following molecules would not readily cross an intact cell membrane by simple diffusion?

A)water
B)glucose
C)oxygen
D)fatty acids
E)ethanol

Question 13

Which is not a model for membrane structure?

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 14

The scientist(s)who developed the "sandwich" model of the cell membrane is (are)

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

Question 15

You are examining an electron micrograph of cells obtained from a new deep-sea life form.Upon closer examination,you notice that there are two dark lines separated by a lightly stained region.These results are similar to the observation of which investigator(s)of membrane structure?

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

Question 16

Based on your knowledge of the chemistry of the cell membrane,which of the following compounds would you couple with a new drug in order to achieve better uptake by cells?

A)carbohydrates
B)polar amino acids
C)lipids
D)several mannose-6-phosphate monomers
E)any hydrophilic substance

Question 17

Which of the following organisms would contain sphingomyelin in its cell membrane?

A)bacteria
B)algae
C)animals
D)bryophytes
E)angiosperms

Question 18

Based on the composition of cell membranes,the most prominent lipids are

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

Question 19

A prokaryotic organism is isolated from a glacier,where it was thriving.Based on your knowledge of the plasma membrane,you would expect to find a predominance of

A)largely saturated fatty acids.
B)equal amounts of saturated and unsaturated fatty acids, as long as the chain was close to 12 carbons in length.
C)cell wall to define the cell because the cell membrane would not be present.
D)largely unsaturated fatty acids.
E)none of the above

Question 20

A prokaryotic organism is isolated from a hydrothermal vent,where it has been observed to be thriving.Based on your knowledge of the plasma membrane,you would expect to find a predominance of

A)largely saturated fatty acids.
B)equal amounts of saturated and unsaturated fatty acids, as long as the chain was close to 12 carbons in length.
C)polar fatty acids.
D)largely unsaturated fatty acids.
E)none of the above

Question 21

The technique that allows various proteins to be differentiated based on size,once the proteins have been denatured,is

A)SDS-PAGE.
B)photobleaching.
C)liposome formation.
D)ferritin-conjugated lectins.
E)the freeze-fracture technique.

Question 22

Which of the following is a sterol-like lipid associated with the cell membrane of prokaryotes?

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

Question 23

A colleague gives you two membrane fractions from a plant cell lysate.One contains the plasma membrane fraction,the other the mitochondrial fraction.The tubes are not labeled,but you run the samples anyway,looking at the macromolecule composition of the samples.You know for certain that the second sample contains the mitochondrial fraction simply because it contains insignificant amounts of

A)lipids.
B)protein.
C)specifically phospholipids.
D)carbohydrates.
E)both choices C and D

Question 24

Membranes contain several classes of lipids,such as phospholipids,sphingolipids,sterols,etc.In spite of their many differences,they all

A)are soluble in nonpolar solvents.
B)can be easily hydrolyzed.
C)are readily soluble in water at 37C.
D)can be reduced by strong reducing agents such as sodium.
E)easily react with bases but not with acids.

Question 25

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 26

Which of the following disorders is the result of impaired glycosphingolipid metabolism?

A)leprosy
B)glycosphingolipid anemia
C)polydactyly
D)tuberculosis
E)Tay-Sachs disease

Question 27

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

A)plasmodesmata.
B)desmids.
C)gap junctions.
D)cell wall pores.
E)connexons.

Question 28

Starting with shredded spinach leaves,you follow a procedure that allows for separation of cellular organelles.You are specifically looking for the fraction that contains the mitochondria.To identify this fraction,you should test for the

A)phospholipids unique to intracellular membranes.
B)general presence of enzymes that fix carbon.
C)phospholipids unique to the mitochondrial membrane.
D)polysaccharides that specifically surround the mitochondria.
E)presence of enzymes associated with cellular respiration.

Question 29

You are experimenting with a variety of lipids to determine their efficacy for use as drug delivery system liposomes.What is one feature of the individual lipid that would best ensure the use of a lipid for this purpose?

A)It must have a structure similar to cholesterol.
B)It must be composed entirely of unsaturated fatty acids.
C)It should be exclusively hydrophilic.
D)It should be amphipathic.
E)It should be exclusively hydrophobic.

Question 30

With respect to the outer and inner faces of the lipid bilayer of the cell membrane,the composition of proteins is

A)asymmetrical.
B)identical.
C)not identical but symmetrical.
D)highly random and varies throughout the cell.
E)a mirror image.

Question 31

To facilitate the regulation of membrane fluidity,E.coli has the enzyme

A)bacteriorhodopsin.
B)desaturase.
C)fatty acid convertase.
D)gangliosidase.
E)unsaturase.

Question 32

Lipid rafts have been associated with which of the following?

A)responses 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

Question 33

A means of detecting the presence of specific carbohydrate moieties on glycoproteins is

A)SDS-PAGE.
B)the freeze-fracture technique.
C)photobleaching.
D)ferritin-conjugated lectins.
E)liposome formation.

Question 34

Localized regions of membrane lipids that contain proteins involved in cell signaling are known as

A)hopanoids.
B)membrane leaflets.
C)homeoviscous adaptations.
D)lipid rafts.
E)islands of hydropathy.

Question 35

Hopanoids

A)are found in eukaryotes only.
B)are related to cholesterol.
C)are a type of glycolipid.
D)are a type of phospholipid.
E)all of the above

Question 36

The venom of black widow spiders (Latrodectus mactans)contains an enzyme that hydrolyzes lecithin to the phospholipid lysolecithin.The lysolecithin lyses red blood cells,destroying them.One possible mechanism whereby lysolecithin disrupts the plasma membranes of red blood cells is that it

A)is toxic to red blood cells.
B)may act in a manner similar to detergents.
C)binds calcium ions, compromising membrane integrity.
D)acts as a second messenger to stimulate apoptosis.
E)None of the above is a possible mechanism.

Question 37

The likely number of and locations of transmembrane segments of integral membrane proteins is inferred by

A)X-ray crystallography.
B)SDS-PAGE.
C)western blot.
D)hydropathic analysis.
E)affinity labeling.

Question 38

Naturally occurring fatty acids are typically

A)saturated.
B)unsaturated.
C)in the trans configuration.
D)in the cis configuration.
E)comprised of an odd number of carbon atoms.

Question 39

Inactivation of a fluorescent dye in a very concentrated spot on a cell so that the fluidity of membranes can be visualized is called

A)liposome formation.
B)SDS-PAGE.
C)photobleaching.
D)the freeze-fracture technique.
E)ferritin-conjugated lectins.

Question 40

Many integral membrane proteins have not been analyzed by X-ray crystallography.
However,transmembrane segments can be inferred using computer analysis of the amino
Acid sequence of the protein.This technique is known as

A)homeoviscous adaptation.
B)lipid analysis.
C)lipid rafting.
D)hydropathic analysis.
E)SDS-PAGE.

Question 41

In E.coli the enzyme responsible for creating unsaturated bonds from saturated ones in the fatty acids of the cell membrane is ________.

Question 42

The shifting of membrane fluidity from a gel-like to a more liquid state is known as ________.

Question 43

Transmembrane proteins involved in detecting external stimuli and relaying that information to the cell are most likely ________ proteins.

Question 44

________ are organisms that are unable to regulate their body temperature.

Question 45

________ are small peptide molecules (10-50 amino acids in length)that affect membrane permeability.

Question 46

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

Question 47

________ is the name given to the technique that utilizes radioactive molecules that bind to specific membrane proteins.

Question 48

Consider the antimicrobial peptides (AMPs)that are classified as cationic and amphipathic as potential novel therapeutic agents in the treatment of leprosy (Mycobacterium leprae).In your response,describe AMPs,where they can be found in nature,and how this specific group of AMPs could be developed into a treatment for leprosy.

Question 49

________ is the name of the technique used for the analysis of membrane lipids.

Question 50

Acholeplasma laidlawii is a bacterium that cannot synthesize its own fatty acids and therefore is dependent upon the available fatty acids in its environment for assembling its own cell wall.Based upon your knowledge regarding the cell membrane,hypothesize the features of the cell membrane of A.laidlawii grown at 37°C under the following conditions: 50/50 mixture of saturated and unsaturated fatty acids,80/20 predominance of saturated fatty acids,80/20 predominance of unsaturated fatty acids,and a 50/50 mixture of saturated and specifically trans fatty acids.

Question 51

________ is a sterol associated with fungal cell membranes.

Question 52

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

Question 53

Trypsin is a hydrophilic protease and therefore is unable to cross the plasma membrane and enter a cell.However,it is capable of digesting the hydrophilic portions of membrane proteins.As a result of these properties,researchers investigating membrane proteins have treated cells with trypsin then separated the proteins by SDS-PAGE to gain insight into the orientation of particular proteins within the membrane.Describe an experiment using this information and the results you would expect with the following types of membrane-associated proteins.(Assume the proteins are single polypeptides.)
a.an integral membrane protein with the N-terminus exposed on the surface
b.an integral membrane protein with the C-terminus exposed on the surface
c.an integral membrane protein with three hydrophilic loops (only)exposed on the surface
d.a membrane-associated protein facing the cytoplasm
e.an imbedded membrane protein

Question 54

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

Question 55

You are a microbiologist working with a recently isolated species of bacteria.You start a culture of the bacterium growing at 15°C.In order to study the membrane composition of this species,you then increase the growth temperature to 37°C.If this bacterium were "typical," what would you expect to see with regard to the fatty acid composition of the membrane?

Question 56

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

Question 57

Most unsaturated fatty acids are in the ________ configuration,but some are in the
________ configuration,making their shape more like that of saturated fatty acids.

Question 58

The presence of trans fats in membranes ________ the transition temperature and ________ membrane fluidity.

Question 59

Recently,consumption of trans fatty acids has been reported to have a link to increased risk of coronary heart disease.What are trans fatty acids? Where are they found in nature? How and why have they been synthetically produced? What effect does their consumption have on humans,and how does that cause the problems associated with coronary heart disease?