Chapter 11 Biological Membranes and Transport
Multiple Choice Questions
1. The composition and architecture of membranes
Which one of the following statements about membranes is true?
A) Most plasma membranes contain more than 70% proteins.
B) Sterol lipids are common in bacterial plasma membranes.
C) Sterol lipids are common in human cell plasma membranes.
D) Sterol lipids are common in plant cell plasma membranes.
E) The plasma membranes of all cell types within a particular organism have basically the same lipid
and protein composition.
2. The composition and architecture of membranes
The inner (plasma) membrane of E. coli is about 75% lipid and 25% protein by weight. How many
molecules of membrane lipid are there for each molecule of protein? (Assume that the average
protein is Mr 50,000 and the average lipid is 750.)
A) 1
B) 50
C) 200
D) 10,000
E) 50,000
3. The composition and architecture of membranes
Which of these statements about the composition of biological membranes is false?
A) In a given eukaryotic cell type (e.g., a hepatocyte), all intracellular membranes have essentially
the same complement of lipids and proteins.
B) The carbohydrate found in membranes is virtually all part of either glycolipids or glycoproteins.
C) The plasma membranes of the cells of vertebrate animals contain more cholesterol than the
mitochondrial membranes.
D) The ratio of lipid to protein varies widely among cell types in a single organism.
E) Triacylglycerols are not commonly found in membranes.
4. The composition and architecture of membranes
Which of these statements about the composition of membranes is true?
A) All biological membranes contain cholesterol.
B) Free fatty acids are major components of all membranes.
C) The inner and outer membranes of mitochondria have different protein compositions.
D) The lipid composition of all membranes of eukaryotic cells is essentially the same.
E) The lipid:protein ratio varies from about 1:4 to 4:1
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5. The composition and architecture of membranes
Membrane proteins:
A) are sometimes covalently attached to lipid moieties.
B) are sometimes covalently attached to carbohydrate moieties.
C) are composed of the same 20 amino acids found in soluble proteins.
D) diffuse laterally in the membrane unless they are anchored
E) have all of the properties listed above.
6. The composition and architecture of membranes
Peripheral membrane proteins:
A) are generally noncovalently bound to membrane lipids.
B) are usually denatured when released from membranes.
C) can be released from membranes only by treatment with detergent(s).
D) may have functional units on both sides of the membrane.
E) penetrate deeply into the lipid bilayer.
7. The composition and architecture of membranes
An integral membrane protein can be extracted with:
A) a buffer of alkaline or acid pH.
B) a chelating agent that removes divalent cations.
C) a solution containing detergent.
D) a solution of high ionic strength.
E) hot water.
The shortest helix segment in a protein that will span a membrane bilayer has about _____ amino
acid residues.
A) 5
B) 20
C) 50
D) 100
E) 200
9. The composition and architecture of membranes
A hydropathy plot is used to:
A) determine the water-solubility of a protein.
B) deduce the quaternary structure of a membrane protein.
C) determine the water content of a native protein.
D) extrapolate for the true molecular weight of a membrane protein.
E) predict whether a given protein sequence contains membrane-spanning segments.
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10. The composition and architecture of membranes
Which of these statements is generally true of integral membrane proteins?
A) The secondary structure in the transmembrane region consists solely of -helices or -sheets.
B) The domains that protrude on the cytoplasmic face of the plasma membrane nearly always have
covalently attached oligosaccharides.
C) They are unusually susceptible to degradation by trypsin.
D) They can be removed from the membrane with high salt or mild denaturing agents.
E) They undergo constant rotational motion that moves a given domain from the outer face of a
membrane to the inner face and then back to the outer.
11. Membrane dynamics
Which of these is a general feature of the lipid bilayer in all biological membranes?
A) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer.
B) Individual lipid molecules in one face (monolayer) of the bilayer readily diffuse (flip-flop) to the
other monolayer.
C) Polar, but uncharged, compounds readily diffuse across the bilayer.
D) The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules.
E) The polar head groups face inward toward the inside of the bilayer.
12. Membrane dynamics
Which of the following are not enzymes involved in moving phospholipids from one leaflet to
another?
A) Flippases that move phosphatidylethanolamine and phosphatidylserine
B) Floppases that move phospholipids from the cytosolic leaflet to the extracellular leaflet
C) Flip-floppases that allow phospholipids to move back and forth between the inner and outer
leaflets
D) Scramblases that allow phospholipids to move down their concentration gradient
E) Phosphatidylinositol transfer proteins that play a role in lipid signaling
13. Membrane dynamics
The fluidity of the lipid side chains in the interior of a bilayer is generally increased by:
A) a decrease in temperature.
B) an increase in fatty acyl chain length.
C) an increase in the number of double bonds in fatty acids.
D) an increase in the percentage of phosphatidyl ethanolamine
E) the binding of water to the fatty acyl side chains.
14. Membrane dynamics
The fluidity of a lipid bilayer will be increased by:
A) decreasing the number of unsaturated fatty acids.
B) decreasing the temperature.
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C) increasing the length of the alkyl chains.
D) increasing the temperature.
E) substituting 18:0 (stearic acid) in place of 18:2 (linoleic acid).
15. Membrane dynamics
When a bacterium such as E. coli is shifted from a warmer growth temperature to a cooler growth
temperature, it compensates by:
A) increasing its metabolic rate to generate more heat.
B) putting longer-chain fatty acids into its membranes.
C) putting more unsaturated fatty acids into its membranes.
D) shifting from aerobic to anaerobic metabolism.
E) synthesizing thicker membranes to insulate the cell.
16. Membrane dynamics
Which of the following statements about caveolin is false?
A) Caveolin is an integral membrane protein.
B) Caveolin induces outward membrane curvature.
C) Caveolin is palmitoylated.
D) Caveolin associates with cholesterol rich regions.
E) Caveolin is involved in membrane trafficking and cellular signaling.
Membrane fusion leading to neurotransmitter release requires the action of:
A) cadherins.
B) selectins.
C) flipases.
D) tSNARE and vSNARE.
E) None of the above
18. Membrane dynamics
Which of the following is not a step involved in neurotransmitter release at a synapse?
A) Creation of a fusion pore
B) Hemifusion induced by zipping and lateral tension on the bilayers
C) v-SNARE binding to t-SNARE
D) Pore widening and release of neurotransmitter
E) Flippase-mediated movement of phosphatidylserine from the inner to the outer leaflet
19. Membrane dynamics
Integrins are:
A) membrane proteins that are involved in ion transport.
B) membrane proteins that are involved in sugar transport.
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C) membrane proteins that mediate cell adhesion.
D) proteins of the extracellular matrix that bind to cell surface proteins.
E) proteins that are found at the membrane-cytoplasm interface.
20. Membrane dynamics
A process not involving the fusion of two membranes or two regions of the same membrane is:
A) endocytosis.
B) entry of enveloped viruses into cells.
C) entry of glucose into cells.
D) exocytosis.
E) reproductive budding in yeast.
21. Solute transport across membranes
Which of these statements about facilitated diffusion across a membrane is true?
A) A specific membrane protein lowers the activation energy for movement of the solute through the
membrane.
B) It can increase the size of a transmembrane concentration gradient of the diffusing solute.
C) It is impeded by the solubility of the transported solute in the nonpolar interior of the lipid bilayer.
D) It is responsible for the transport of gases such as O2, N2, and CH4 across biological membranes.
E) The rate is not saturable by the transported substrate.
22. Solute transport across membranes
Facilitated diffusion through a biological membrane is:
A) driven by a difference of solute concentration.
B) driven by ATP.
C) endergonic.
D) generally irreversible.
E) not specific with respect to the substrate
23. Solute transport across membranes
Glucose transport into erythrocytes is an example of:
A) active transport.
B) antiport.
C) electrogenic uniport
D) facilitated diffusion.
E) symport.
For the process of solute transport, the constant Kt is:
A) analogous to Ka for ionization of a weak acid.
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B) analogous to Km for an enzyme-catalyzed reaction.
C) analogous to Vmax for an enzyme reaction
D) proportional to the number of molecules of glucose transporter per cell.
E) the maximum rate of glucose transport.
25. Solute transport across membranes
Which of the following statements is not true about the chloride-bicarbonate exchanger (AE)?
A) The AE protein increases the rate of bicarbonate transport across the membrane.
B) The AE protein uses ATP as an energy source to drive bicarbonate transport.
C) The AE protein transports chloride ions across the membrane.
D) The AE protein is classified as an anti-porter.
E) The AE protein spans the membrane at least 12 times.
26. Solute transport across membranes
The type of membrane transport that uses ion gradients as the energy source is:
A) facilitated diffusion
B) passive transport.
C) primary active transport.
D) secondary active transport.
E) simple diffusion.
27. Solute transport across membranes
Consider the transport of glucose into an erythrocyte by facilitated diffusion. When the glucose
concentrations are 5 mM on the outside and 0.1 mM on the inside, the free-energy change for glucose
uptake into the cell is: (These values may be of use to you: R = 8.315 J/mol·K; T = 298 K; 9
(Faraday constant) = 96,480 J/V; N = 6.022 1023/mol.)
A) less than 2 kJ/mol.
B) about 10 kJ/mol.
C) about 30 kJ/mol.
D) about –30 kJoule/mol.
E) impossible to calculate without knowledge of the membrane potential.
28. Solute transport across membranes
Consider the transport of K+ from the blood (where its concentration is about 4 mM) into an
erythrocyte that contains 150 mM K+. The transmembrane potential is about 60 mV, inside negative
relative to outside. The free-energy change for this transport process is: (These values may be of use
to you: R = 8.315 J/mol.K; T = 298 K; 9 (Faraday constant) = 96,480 J/V; N = 6.022 1023/mol.)
A) about 5 J/mol.
B) about 15 J/mol.
C) about 5 kJ/mol.
D) about 15 kJ/mol.
E) impossible to calculate with the information given.
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29. Solute transport across membranes
An electrogenic Na+ transporter:
A) catalyzes facilitated diffusion of Na+ from a region of high Na+ concentration to one of lower Na+
concentration.
B) must catalyze an electron transfer (oxidation-reduction) reaction simultaneously with Na+
transport.
C) must transport both Na+ and a counterion (Cl–, for example).
D) transports Na+ against its concentration gradient.
E) transports Na+ without concurrent transport of any other charged species.
30. Solute transport across membranes
In one catalytic cycle, the Na+/K+ ATPase transporter transports:
A) 2 Na+ out, 3 K+ in, and converts 1 ATP to ADP + Pi.
B) 3 Na+ out, 2 K+ in, and converts 1 ATP to ADP + Pi.
C) 3 Na+ in, 2 K+ out, and converts 1 ATP to ADP + Pi.
D) 1 Na+ out, 1 K+ in, and converts 1 ATP to ADP + Pi.
E) 2 Na+ out, 3 K+ in, and converts 1 ADP + Pi to ATP.
31. Solute transport across membranes
ABC transporters are not known to facilitate the following process:
A) moving cancer drugs out of cancer cells.
B) moving antibiotics out of bacteria.
C) moving membrane lipids from the inner leaflet to the outer leaflet.
D) moving chloride ions in the lung.
E) moving vitamin E into lipocytes.
32. Solute transport across membranes
Movement of water across membranes is facilitated by proteins called:
A) annexins.
B) aquaporins.
C) hydropermeases.
D) selectins.
E) transportins.
33. Solute transport across membranes
The specificity of aquaporins for water is not ensured by which of the following?
A) The channel contains a negatively charged Asp residue to scavenge protons and H3O+.
B) The diameter of the channel narrows to 2.8 Å.
C) There are carbonyl backbone residues in the channel that hydrogen bond with water.
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D) Arg and His residues in the channel repel protons and H3O+.
E) Electric dipoles of short -helices repel protons and H3O+.
34. Solute transport across membranes
The specificity of the potassium channel for K+ over Na+ is mainly the result of the:
A) differential interaction with the selectivity filter protein.
B) hydrophobicity of the channel.
C) phospholipid composition of the channel.
D) presence of carbohydrates in the channel.
E) presence of cholesterol in the channel.
35. Solute transport across membranes
A ligand-gated ion channel (such as the nicotinic acetylcholine receptor) is:
A) a charged lipid in the membrane bilayer that allows ions to pass through.
B) a membrane protein that permits a ligand to pass through the membrane only when opened by the
appropriate ion.
C) a membrane protein that permits an ion to pass through the membrane only when opened by the
appropriate ligand.
D) a molecule that binds to the membrane thereby allowing ions to pass through.
E) always requires a second ligand to close the channel once it is opened.
Short Answer Questions
36. The composition and architecture of membranes
Page: 386 Difficulty: 3
The plasma membrane of an animal cell consists of 45% by weight of phospholipid and 55% protein.
What is the mole ratio (moles of lipid/moles of protein) if the average molecular weight of
phospholipids is 750 and the average molecular weight of membrane proteins is 50,000?
37. The composition and architecture of membranes
Page: 386 Difficulty: 2
(a) List three different major components of eukaryotic membranes. (b) When a preparation of
mitochondrial membranes was treated with high salt (0.5 M NaCl), it was observed that 40% of the
total protein in this preparation was solubilized. What kind of membrane proteins are in this soluble
extract, and what forces normally hold them to the membrane? (c) What kind of proteins constitute
the insoluble 60%, and what forces hold these proteins in the membrane?
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38. The composition and architecture of membranes
Pages: 389–395 Difficulty: 2
What are the principle features of the fluid mosaic model of membranes?
39. The composition and architecture of membranes
Pages: 389-395 Difficulty: 3
Draw the structure of a biological membrane as proposed by the fluid mosaic model. Indicate the
positions and orientations of phospholipids, cholesterol, integral and peripheral membrane proteins,
and the carbohydrate moieties of glycoproteins and glycolipids.
40. The composition and architecture of membranes
Page: 387 Difficulty: 2
What is an amphipathic compound? Explain how such compounds contribute to the structure of
biological membranes.
41. The composition and architecture of membranes
Pages: 387–388 Difficulty: 2
(a) When relatively high concentrations of fatty acids are suspended in water, they form structures
known as ________. (b) When relatively high concentrations of membrane phospholipids are
dissolved in water, they form structures known as ________. (c) Why are the structures listed in your
answers to (a) and (b) above energetically favored?
42. The composition and architecture of membranes
Page: 388 Difficulty: 3
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(a) Explain why phosphoglycerides are capable of spontaneously assembling into the bilayer structure
found in biological membranes but triacylglycerols are not. (b) What are the forces that drive bilayer
formation?
43. The composition and architecture of membranes
Pages: 389–391 Difficulty: 3
Reagents A and B both react covalently with primary amino groups such as those of
phosphatidylethanolamine. Reagent A permeates erythrocytes, but reagent B is impermeant. Both A
and B are available in radioisotopically labeled form. Describe a simple experiment by which you
might determine whether the phosphatidylethanolamine of erythrocyte membranes is located in the
outside face of the lipid bilayer, the inside face, or in both.
44. The composition and architecture of membranes
Pages: 389–391 Difficulty: 1
Explain the differences between integral and peripheral membrane proteins.
45. The composition and architecture of membranes
Pages: 389–391 Difficulty: 2
(a) What kinds of forces or bonds anchor an integral membrane protein in a biological membrane?
(b) What forces hold a peripheral membrane protein to the membrane? (c) What might one do to
solubilize each of the two types of membrane proteins?
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46. The composition and architecture of membranes
Page: 392 Difficulty: 2
A protein is found to extend all the way through the membrane of a cell. Describe this protein in
terms of the location of particular types of amino acid side chains in its structure and its ability to
move within the membrane.
47. The composition and architecture of membranes
Page: 392 Difficulty: 2
If the hydrophobic interior of a membrane were about 3 nm thick, what would be the minimum
number of amino acids in a stretch of transmembrane helix?
48. The composition and architecture of membranes
Page: 392 Difficulty: 2
Draw a hydropathy plot for a hypothetical integral membrane protein with 3 transmembrane segments
and containing 190 amino acids. Be sure to label the x– and y-axes appropriately, including numerical
values.
49. The composition and architecture of membranes
Pages: 389–395 Difficulty: 3
You are trying to isolate an enzyme that catalyzes the conversion of A → B, and you have a sensitive
assay for this enzyme. After lysing open the cells, you find that the activity is associated with the
membrane fraction, not the soluble fraction (which you throw away). You then follow the procedure
shown below. Explain the sudden re-occurrence of activity at the end of your protocol.
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50. Membrane dynamics
Page: 396 Difficulty: 2
The bacterium E. coli can grow at 20 °C or at 40 °C. At which growth temperature would you expect
the membrane phospholipids to have a higher ratio of saturated to unsaturated fatty acids, and why?
51. Membrane dynamics
Pages: 395–396 Difficulty: 2
Describe two different ways a plant can adjust the components of its cell membranes to keep them as
fluid as possible on a cold winter morning.
52. Membrane dynamics
Pages: 395–396 Difficulty: 2
A plant breeder has developed a new frost-resistant variety of tomato that contains higher levels of
unsaturated fatty acids in membrane lipids than those found in standard tomato varieties. However,
when temperatures climb above 95 °F, this frost-resistant variety dies, whereas the standard variety
continues to grow. Provide a likely explanation of the biochemical basis of increased tolerance to
cold and increased susceptibility to heat of this new tomato variety.
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53. Membrane dynamics
Pages: 395–396 Difficulty: 2
a) What is meant by the transition temperature of a membrane? List the two characteristics of the
fatty acids in a biological membrane that affect the transition temperature. Using or , show in
which direction an increase in these characteristics would change the transition temperature.
54. Membrane dynamics
Pages: 398–400 Difficulty: 2
Glycosphingolipids and cholesterol cluster together in membrane regions known as “__________.”
These microdomains are more __________ than the surrounding phospholipid-rich membrane due to
a high content of __________ fatty acids. These regions are rich in proteins that are anchored to the
membrane by covalently attached __________ and __________ groups and also those anchored by
GPI linkage. Proteins aggregated in this fashion are often functionally related. Examples are (1)
__________ proteins and (2) __________ proteins.
55. Membrane dynamics
Pages: 399–402 Difficulty: 3
What are the similarities and differences between integrins, cadherins, and selectins?
56. Solute transport across membranes
Pages: 402–405 Difficulty: 3
Distinguish between simple diffusion (SD), facilitated diffusion (FD), and active transport (AT)
across a membrane for the following questions. (More than one may be true.)
(a) Which processes are energy dependent?
(b) Which processes need some kind of carrier protein(s)?
(c) Which processes can be saturated by substrate?
(d) Which processes can establish a concentration gradient?
(e) How much energy does it take to transport an uncharged substrate in, if its starting inside
concentration is 10-fold greater than outside?
57. Solute transport across membranes
Page: 403 Difficulty: 2
Explain why nonpolar compounds are generally able to diffuse across biological membranes without
the aid of a specific transport system.
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58. Solute transport across membranes
Pages: 405–407 Difficulty: 3
Compare the structure and activity of a membrane transport protein that transports a polar substance
across a membrane with a typical soluble enzyme. How are transporter and enzyme similar? How
are they different?
59. Solute transport across membranes
Pages: 405–407 Difficulty: 3
Transport of histidine into a bacterial cell was measured at several different histidine concentrations.
Does histidine uptake operate by passive or facilitated transport, and why?
Histidine (µM)
Transport (µM/min)
2.5
42.5
7
119
16
240
31
490
72
1000
60. Solute transport across membranes
Pages: 411–412 Difficulty: 3
Compare and contrast symport and antiport. Which term best describes the transport system mediated
by the Na+K+ ATPase?
61. Solute transport across membranes
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Pages: 397–398, 420–423 Difficulty: 2
What are three differences between ion channels and ion transporters?
62. Solute transport across membranes
Pages: 420–424 Difficulty: 3
What is the major difference between gated and non-gated ion channels? Give an example of two
different gating signals.