Deck 12: Biological Membranes: Structure and Membrane Transport

Question 1

Effects of cholesterol on phospholipid bilayers include all of the following EXCEPT

A) eliminates the thermotropic phase transition.
B) rigidifies membranes which are initially fluid.
C) fluidizes membranes which are initially liquid-crystalline.
D) orients hydroxyl groups near charged phosphodiester functions.

Answer 1

fluidizes membranes which are initially liquid-crystalline.

Question 2

Induces the dephosphorylation of the phosphorylated Na^+--K⁺- ATPase (E~P)

A) K⁺
B) Na⁺
C) ATP^4-
D) Ca²⁺
E) phosphoenolpyruvate (PEP)

Answer 2

K⁺

Question 3

Which of the following statements about the composition of red cell membranes is correct?

A) As with plant cell membranes, cholesterol is present only in traces.
B) As a group, the glycerol phosphatides (PTC, PTE, PTS) are the quantitatively major lipid component.
C) Proteins are found as extrinsic proteins on both the inner and outer surfaces of the lipid bilayer.
D) Oligosaccharide chains of glycolipids project from both the inner and outer surfaces of the lipid bilayer.
E) Sphingomyelins are uniformly distributed between the inner and outer layers of the lipid bilayer.

Answer 3

As a group, the glycerol phosphatides (PTC, PTE, PTS) are the quantitatively major lipid component.

Question 4

The transport system that maintains the sodium gradient across the cell membrane:

A) involves an ATPase enzyme.
B) is a symport system with glucose as a cotransported solute.
C) moves sodium into the cell.
D) hydrolyzes ATP in the membrane, in a mechanism independent of the movement of sodium ion.
E) is an antiport system that derives its energy from high concentrations of glucose.

Question 5

A new transport protein is found to undergo a cycle of phosphorylation-dephosphorylation during the movement of selenium ion into cells. To which of the following would you expect the sequence of this protein to be related ?

A) the anion transport protein
B) the Ca²⁺- ATPase
C) the glucose transport protein
D) an amino acid cotransporter
E) the mitochondrial coupling factor

Question 6

Phosphatides may contain glycerol in ester linkage to two fatty acids, and in phosphodiester linkage with which of the following alcohols?

A) choline, serine, ethanolamine
B) choline, sphingosine, serine
C) serine, cholesterol, choline
D) All of the above.
E) None of the above.

Question 7

The erythrocyte membrane

A) contains phosphatidylserine as the major glycerophospholipid.
B) contains anion exchange protein as the major peripheral protein.
C) exhibits restricted lateral diffusion of major integral proteins.
D) facilitates permeability of glucose through the lipid regions.
E) permits rapid transverse diffusion of lipid molecules.

Question 8

All of the following statements about facilitated diffusion are correct EXCEPT

A) a plot of rate of uptake by cells of the pertinent substance would be expected to give a hyperbolic curve.
B) depending on conditions, transport could occur in either direction across the membrane.
C) the process can allow a substance in cells to be accumulated against a concentration gradient.
D) an interaction between the substance transported and a membrane component is likely to occur.
E) competitive inhibition of the transport of a substance by its chemical analogs is likely to occur.

Question 9

A characteristic among all mammalian glucose transporters (GLUTs) is

A) a high affinity for binding glucose.
B) a transmembrane, hydrophilic pore.
C) expression in the liver.
D) gating by Ca²⁺.
E) regulation by insulin.

Question 10

The complete hydrolysis of phosphatidylcholine, isolated from a plasma membrane, would be expected to result in the formation of

A) sphingosine, phosphoric acid, choline and a mixture of saturated and unsaturated fatty acids.
B) glycerol, phosphoric acid, choline and saturated fatty acids only.
C) glycerol, phosphoric acid, choline and unsaturated fatty acids only.
D) glycerol, phosphoric acid, choline and a mixture of saturated and unsaturated fatty acids.
E) sphingosine, phosphoric acid, choline and galactose.

Question 11

Cholesterol, phosphatidylserine, and palmitate have in common

A) a phosphate group.
B) a hydrophobic unit.
C) an acyl chain.
D) a carboxylate group.
E) a free hydroxyl group.

Question 12

The lateral diffusion of an integral membrane protein is

A) decreased by interactions with peripheral proteins.
B) increased as the fatty acyl residues of membrane phospholipids become more saturated.
C) decreased relative to that of a phospholipid because of the large difference in molecular size.
D) increased as a consequence of fluorescence recovery after photobleaching.

Question 13

Lipid rafts tend to be thicker than the rest of the membrane. What causes this?

A) High cholesterol
B) High glycosphingolipids
C) High plasmalogen
D) High protein content
E) High unsaturated fatty acids

Question 14

All of the following statements about lipid bilayer membranes are correct, EXCEPT

A) cholesterol can decrease the fluidity of a membrane.
B) water molecules can diffuse through a lipid bilayer.
C) lipids can readily diffuse laterally in the membrane.
D) lipids can rotate end-over-end (Flip-Flop) easily.
E) all major components of a lipid membrane show asymmetric arrangement.

Question 15

Which of the following statements about transport across plasma membranes of cells is correct?

A) Facilitated diffusion transport systems are bidirectional with the direction of net transport being determined by the concentration gradient.
B) A variety of small compounds such as glucose and other sugars enter cells primarily by simple diffusion.
C) All examples of mediated transport involve vectorial or one-way transport across the membrane.
D) In the absence of specific transport systems, a small hydrophobic compound would be expected to cross a membrane more slowly than a hydrophilic molecule of similar size.
E) Ions such as chloride and bicarbonate cross membranes very slowly.

Question 16

Chloride transport through the CFTR protein is

A) gated by the binding of guanine nucleotides.
B) linked to a cotransport (antiport) of phosphate.
C) localized to the endoplasmic reticulum of normal epithelial cells.
D) regulated by phosphorylation and dephosphorylation of Ser residues.

Question 17

In biological membranes the PREDOMINANT interaction between the proteins and phospholipids is probably

A) hydrogen bonding.
B) hydrophobic interaction.
C) ionic interactions.
D) covalent linkages.

Question 18

The movement of Na⁺ and K⁺ across the plasma membrane protons by Na⁺K⁺-ATPase is an example of what type of transport?

A) passive diffusion
B) facilitated diffusion
C) active antiport cotransport
D) active symport cotransport
E) mass transit

Question 19

In the fluid-mosaic model of membrane structure

A) ionic and polar heads of lipid molecules are in the interior core of the membrane.
B) the membrane is symmetrical in that the outer face is identical to the cytoplasmic face in terms of phospholipid and protein composition.
C) integral membrane proteins are in contact with the fatty acid chains of the phospholipids.
D) peripheral membrane proteins are situated in the hydrophobic core.

Question 20

Integral membrane proteins that exhibit an intrinsic activity of hydrolyzing ATP to ADP and Pi most likely participate in

A) binding polypeptide hormones.
B) generating intracellular messengers during signal transduction.
C) initiating one or more steps in blood coagulation.
D) moving cations against their concentration gradient.
E) targeting proteins to different organelles.

Question 21

Phosphoglycerides

A) always contain a nitrogen base.
B) are derivatives of phosphatidic acid.
C) are derivatives of terpenes.
D) are non-saponifiable.
E) are usually phosphate-free.

Question 22

Simple diffusion of a substance across a biological membrane

A) shows saturation kinetics.
B) is a linear function of the concentration difference across the membrane.
C) can be inhibited by the addition of a compound of similar chemical structure.
D) is dependent on the concentration of other solutes in the system.
E) is mediated by membrane carriers.

Question 23

A typical transmembrane domain in a protein is

A) an alpha helix containing mostly aromatic amino acids.
B) an alpha helix containing a mixture of nonpolar amino acids.
C) a beta sheet containing alternating polar and nonpolar amino acids.
D) a beta sheet containing mostly nonpolar amino acids.

Question 24

A structural feature common to all membrane forming lipids is

A) charged groups.
B) fatty acyl groups.
C) hydroxyl groups.
D) amphipathic character.
E) detergent property.

Question 25

The organization of the glycerophospholipid phosphatidylserine in an aqueous environment is a

A) monomer with the serine and fatty acyl residues exposed to water.
B) micelle with the serine residues exposed to water.
C) micelle with the serine residues sequestered from water.
D) bilayer with the fatty acyl residues exposed to water.
E) bilayer with the fatty acyl residues sequestered from water.

Question 26

All of the following enter or leave mitochondria via a specific transport protein EXCEPT

A) ATP.
B) inorganic phosphate.
C) pyruvate.
D) malate.
E) oxygen.

Question 27

The protein that is defective in cystic fibrosis normally functions as

A) a chloride transporter protein.
B) a G-protein.
C) a receptor for insulin.
D) a sodium, potassium ATPase.
E) an endoplasmic reticulum calcium pump.

Question 28

Membranes will have their greatest fluidity when which one of the following is present in the phospholipids?

A) palmitic acid
B) stearic acid
C) arachidonic acid
D) linoleic acid
E) oleic acid

Question 29

In treating a patient with congestive heart failure, you have prescribed digoxin (a cardiac glycoside) to strengthen the heart's output and maintain a regular rate. The target of this drug is the

A) ATP synthase.
B) Na⁺, K⁺ - ATPase.
C) ligand - gated Ca²⁺ channel.
D) resting K⁺ channel.
E) voltage - gated Na⁺ channel.

Question 30

All of the following statements about a facilitated diffusion transport system are correct EXCEPT

A) like an enzyme, the system would display saturation or Michaelis-Menten kinetics.
B) transport of a compound would be expected to be inhibited by a close chemical analogue.
C) transport would be vectorial or one-way.
D) the system would be expected to be quite specific, i.e., it would be expected to transport only one or a few closely-related compounds.
E) a mutation, expressed as the loss of ability to make a certain membrane protein, could result in loss of ability of a cello take up a given compound.

Question 31

Phospholipids have the property of detergency. This is due primarily to

A) polar head groups.
B) a hydrocarbon tail.
C) an amphipathic nature.
D) solubility

Question 32

Each of the following lipid types is a membrane constituent EXCEPT which one?

A) sphingolipids
B) phospholipids
C) gangliosides
D) triglycerides
E) cholesterol

Question 33

Which of the following is most likely to cross a membrane by a non-mediated diffusion process?

A) glucose
B) carbon dioxide
C) sodium ions out of cells
D) ADP
E) ATP

Question 34

Which statement is NOT characteristic of an active transport system for L-alanine in animal cells?

A) L-alanine is transported against a concentration gradient.
B) A carrier protein is required to recognize and bind L-alanine.
C) It is blocked by inhibitors of oxidative phosphorylation.
D) It transports D- and L-alanine with equal facility.
E) It is functional in renal tubular cells.

Question 35

All of the following are generally accepted as features of the fluid-mosaic model of membrane structure EXCEPT

A) asymmetrical arrangement of lipids.
B) rapid diffusion of inorganic ions across the lipid bilayer
C) rapid lateral diffusion of lipids.
D) slow lateral diffusion of integral and peripheral proteins.
E) infrequent transverse (flip-flop) movement of lipids from one face of the bilayer to the other.

Question 36

Differences in bilayer fluidity among human cell membranes are due to

A) changes in membrane potential resulting from ATP-driven ion pumps.
B) fluctuations in body temperature.
C) interactions between phosphatidylethanolamine and divalent cations.
D) the level of monoacylglycerol.
E) the ratio of cholesterol to phospholipids.

Question 37

The formation in humans of specific membrane microdomains depends on all of the following EXCEPT

A) chemical characteristics of lipids.
B) lateral mobility of proteins.
C) lipid anchors on proteins.
D) temperature and pressure.
E) transbilayer asymmetry of lipids and proteins.

Question 38

The mechanism of action of many anesthetics is now thought to involve a

A) change in the organization (order) of membrane lipids.
B) specific interaction with integral membrane proteins.
C) direct influence on the active transport rate.
D) plugging of the sodium channels.

Question 39

Which phospholipid would migrate closest to the plus (+) electrode in an electrophoresis cell at pH 7?

A) phosphatidylserine.
B) phosphatidylcholine.
C) phosphatidylethanolamine.
D) phosphatidylinositol.
E) phosphatidylglycerol.

Question 40

The asymmetry associated with biological membranes refers to the

A) degree of lateral mobility of integral membrane proteins.
B) ratio of phospholipid to cholesterol.
C) differences in protein and lipid composition of the outer and inner leaflet of the membrane bilayer.
D) ratio of peripheral to integral membrane protein.

Question 41

Which of the following is true for Glycophorin?

A) the oligosaccharides are evenly distributed along the peptide chain.
B) the carboxy terminal end is always projecting to the inside of the cell.
C) is a peripheral glycoprotein of human erythrocyte membranes.
D) is a chloride transport protein.

Question 42

The observation that plasma membrane components mix after fusion of two different cells provides evidence for

A) bilayer structure of biological membranes.
B) lateral mobility of membrane proteins.
C) relative asymmetry of membrane lipids.
D) rotational movement of membrane proteins.
E) transbilayer movement of membrane lipids.

Question 43

Which of the following characteristics is typical of the fluid Mosaic model of membrane structure?

A) The proteins are all spread in a sheet over the surface of the lipid bilayer.
B) The proteins are all attached as spherical molecules to the surface of the membrane.
C) Some proteins have polypeptides consisting predominantly of nonpolar residues in the interior of the membrane.
D) All proteins are loosely attached to the exterior and interior surfaces of the lipid bilayer.
E) None of the above is true.

Question 44

Source of energy in the phosphotransferase system of active transport of sugars in bacteria is

A) K ⁺
B) Na⁺
C) ATP^4-
D) Ca²⁺
E) phosphoenolpyruvate (PEP)

Question 45

In the fluid Mosaic model of membrane structure, which one of the following compounds serves as the binding sites for the peripheral membrane proteins?

A) Cholesterol
B) phosphatidyl choline
C) Glycolipids
D) phosphatidyl serine
E) Integral membrane proteins

Question 46

Proteins in membranes

A) are located only at the external surface of the membrane.
B) have carboxy termini is usually oriented toward the exterior part of the cell.
C) consist of a small number of low molecular weight proteins.
D) are located both on the surface and in the interior of the membrane.
E) are located only in the internal portion of the membrane.

Question 47

Regarding the Na⁺ - K⁺ ATPase pump:

A) Na⁺ and Mg²⁺ are required for dephosphorylation of the phosphorylated enzyme.
B) K⁺ is required for phosphorylation of the enzyme by ATP.
C) Both
D) Neither

Question 48

The uptake of a substance across a biological membrane by simple diffusion

A) exhibits saturation kinetics.
B) is at a rate which is a linear function of the concentration difference across the membrane.
C) can be inhibited by blockers of oxidative phosphorylation.
D) is mediated by membrane proteins which bind the substance.

Question 49

Optimal hydrophobic interactions between the interior of a lipid bilayer and a membrane protein would be achieved with which of the following groups of amino acids?

A) Ala, Arg, Asp
B) Cys, His, Pro
C) Gln, Glu, Gly
D) Ile, Met, Trp
E) Ser, Thr, Tyr

Question 50

The carbohydrate moieties of glycoprotein components of the plasma membranes of cells are bound only to

A) asparaginyl residues.
B) serine and threonine residues.
C) parts of the protein that project from the cytoplasmic face of the membrane.
D) parts of the protein that project from the non-cytoplasmic (extracellular) face of the membrane.

Question 51

Cardiac glycosides such as ouabain stimulate cardiac contraction. The molecular basis of the effect of these compounds is believed to result from which of the following?

A) They act as monovalent cation ionophores.
B) They cause an increase in the fluidity of the plasma membrane.
C) They inhibit the efflux of calcium ions from the cell.
D) They inhibit the Na⁺,K⁺-ATPase enzyme.
E) They become intercalated into the plasma membrane, rendering it leaky.

Question 52

Typical components of a plasma membrane include all of the following EXCEPT

A) cholesterol
B) sphingomyelin
C) proteins
D) triglycerides
E) phospholipids

Question 53

Which of the following pairs of compounds are components of a phospholipid?

A) CDP and inositol
B) monoglyceride and choline
C) phosphatidic acid and CDP
D) phosphatidic acid and ethanolamine
E) sphingosine and lecithin

Question 54

A principal difference between facilitated and active transport systems in membranes is the

A) direction of solute movement relative to its concentration gradient.
B) kinetics of the process.
C) number of transmembrane domains in the transport proteins.
D) sensitivity to inhibition.
E) specificity and binding affinity toward the solute being transported.

Question 55

Membrane fluidity

A) increases as the percent of unsaturated fatty acids increases.
B) increases as the percent of unsaturated fatty acids decreases.
C) increases as the length of fatty acid side chains increases.
D) is independent of the nature of fatty acids.
E) increases as the percent of saturated fatty acids increases.

Question 56

All of the following statements about integral membrane proteins are true EXCEPT

A) they are associated with lipid in the membrane.
B) they can be transmembranous.
C) they are amphipathic.
D) they are symmetrically distributed within the membrane.
E) they are only removed from the membrane by drastic treatments.

Question 57

Which one of the following membranes contains the highest percentage of lipid?

A) Endoplasmic reticulum
B) Erythrocyte plasma membrane
C) Myelin sheath
D) Inner mitochondrial membrane
E) Outer mitochondrial membrane

Question 58

Phospholipids and glycolipids in membranes are organized primarily as

A) a micelle.
B) a monomolecular sheet.
C) a trimer.
D) a bimolecular sheet.
E) none of the above.

Question 59

At physiological pH, phosphatidylinositol would exist mainly as a species with a net charge of:

A) +1
B) -2
C) -1
D) +2
E) 0

Question 60

Which of the following properties is characteristic of an active transport system?

A) carrier-mediated
B) solute transported against a concentration gradient
C) transport inhibited by compounds which are structurally similar to the normally transported solute
D) stereospecificity
E) all of the above

Question 61

How does the cell maintain a higher level of K⁺ than of Na⁺?

A) The Na⁺ leaks out into the surrounding extracellular fluid.
B) K⁺ is bound to sites inside the cell.
C) The body contains less total Na⁺ than K⁺, so Na⁺ is found at a low concentration inside the cell.
D) Na⁺ is actively transported out of the cell and K⁺ actively transported in the cell.
E) Much of the Na⁺ outside the cell is bound to protein, so that no Na+ gradient exists across the cell membrane.

Question 62

The major contribution to the favorable free energy of self-association of phospholipids in aqueous media is

A) ion-pair formation
B) electrostatic repulsion
C) hydrophobic free energy
D) charge-transfer interactions
E) All of the other answers are correct

Question 63

The movement of glucose across the erythrocyte membrane is an example of

A) non-mediated transport.
B) passive mediated transport.
C) direct active mediated transport.
D) indirect active mediated transport.
E) altered molecule mediated transport (group translocation).

Question 64

Which is NOT an intrinsic (integral) membrane protein of mammalian cells?

A) spectrin
B) Na⁺/K⁺ ATPase
C) band 3 protein of the erythrocyte
D) ADP/ATP exchange protein of mitochondria
E) LDL receptor

Question 65

The structure of a biological membrane is best described as

A) a continuous bilayer of lipids coated with proteins on either side.
B) a fluid mosaic of proteins interspersed in a lipid bilayer.
C) a phospholipid bilayer with interspersed proteins, held together by covalent and H-bonds.
D) a phospholipid bilayer with the hydrophilic groups turned inward, hydrophobic groups outward.
E) an internal layer of protein surrounded by a sheet of lipids.

Question 66

To what superfamily of transporters do the P-glycoproteins belong?

A) ABC (ATP-binding cassette)
B) Calmodulin-associated
C) Glyceroaquaporins
D) Ionophores
E) Secondary active

Question 67

Certain lipid molecules covalently attached to a protein may anchor that protein to the cell membrane. Each of the following lipids have been shown to function in this capacity, EXCEPT:

A) Covalently attached myristate
B) Covalently attached farnesyl group
C) Covalently attached phosphatidyl inositol
D) Covalently attached cholesterol
E) Covalently attached palmitate

Question 68

Phosphorylation of the Na⁺ - K⁺ ATPase promotes a conformational change in which:

A) The phosphorylated conformation has a low binding affinity for Na⁺.
B) The phosphorylated conformation has a high binding affinity for K⁺.
C) Both
D) Neither

Question 69

Which of the following characteristics best describes the lipid molecules in biological membranes?

A) amphipathic
B) complexed with Ca²⁺
C) fluid
D) unsaturated
E) zwitterionic

Question 70

What phrase describes a nutrient transport system that behaves similar to enzymes, requires energy and moves the nutrient in one direction?

A) Simple diffusion
B) Active transport
C) Facilitated diffusion
D) Exchange diffusion
E) None of the above

Question 71

Analysis of an unknown compound yielded fatty acid, sphingosine, phosphate and choline in equimolar ratios. The compound is most likely

A) a triacylglycerol.
B) phosphatidyl choline.
C) a cerebroside.
D) a sphingomyelin.
E) lysophosphatide.

Question 72

Which of the following compounds could easily be converted into lipid bilayer vesicles?

A) bile salts
B) cholesterol
C) diacyl glycerol
D) lecithin
E) Stearate

Question 73

How is the voltage-sensing area of a voltage-gated ion channel seen in a 3D diagram?

A) A transmembrane segment surrounded by 5 other transmembrane segments
B) All transmembrane segments except one grouped together
C) Four transmembrane segments adjacent to each other
D) One transmembrane segment in the center of 3 other segments
E) The first and last transmembrane segment of each homologous domain in the center of the structure

Question 74

The only FALSE statement about membrane proteins is:

A) Some membrane-bound proteins are anchored to the lipid bilayer via a covalent attachment to the membrane lipid phosphatidyl inositol.
B) Carbohydrate on membrane lipids and proteins is symmetrically distributed across the plasma membrane.
C) Peripheral membrane proteins are asymmetrically distributed across the plasma membrane.
D) transport proteins generally span the lipid bilayer multiple times.
E) The membrane-spanning domain of a transmembrane protein is usually an alpha-helix.

Question 75

Gap junctions, important for intercellular communication, can function as follows:

A) They can be open or closed depending on the appropriate level of signal (e.g., Ca²⁺).
B) They can allow molecules of up to 1,000 Daltons (molecular weight) pass from one to another of interconnected cells.
C) Both
D) Neither

Question 76

Bilayer-forming glycerophospholipids

A) are found exclusively in the plasma membrane.
B) exhibit rapid transverse diffusion across the membrane.
C) have two fatty acyl groups.
D) rarely participate in non-covalent bonds with proteins.
E) readily assemble in water into micelles.

Question 77

A relatively low protein concentration is found in the myelin sheath because

A) the functional role of proteins in myelin is limited to ion channels.
B) proteins principally serve as structural components.
C) the large ganglioside molecules do not leave enough room for proteins.
D) hydrophilic and hydrophobic interactions cannot occur.

Question 78

Provides structural rigidity to the plasma membrane.

A) Cholesterol
B) palmitate
C) arachidonate
D) diacylglycerol
E) oleate

Question 79

An alpha-helix conformation is favored in the transmembrane domain of a membrane protein because:

A) Intramolecular H-bonding can occur, stabilizing the alpha?helix.
B) Within the core of the lipid bilayer, there are no other molecules which can form H-bonds and thus compete with the intramolecular H-bonds of the transmembrane peptide domain.
C) Both
D) Neither

Question 80

Lipid bilayers

A) form spontaneously by the cooperative assembly of amphipathic molecules in water.
B) form from phosphatidylcholine in an organic solvent such as chloroform.
C) have the thickness of one molecule of phosphoglyceride or sphingolipid.
D) are more permeable to small ions such as Na⁺ than to larger molecules such as glucose.
E) are about 2 A thick.