Chapter 12 Membrane Structure and Function
Matching Questions
Use the following to answer questions 1-10:
Choose the correct answer from the list below. Not all of the answers will be used.
a) glycolipids
b) biomolecular sheets
c) lateral diffusion
d) integral
e) hydrophobic effect
f) acetylsalicylic acid (aspirin)
g) water
h) lipid raft
i) hydrophobic
j) ions
k) high
l) peripheral
m) low
1.
Lipid biolayers spontaneously form ____________.
2.
The driving force for the formation of membrane bilayers.
Ans: e.
Section: 12.1
3.
________ has a higher permeability through lipid bilayers than ions and most polar molecules.
Section: 12.1 and Figure 12.4
4.
____________membrane proteins are embedded in the hydrocarbon chains of membrane lipids.
Ans: d
Section: 12.3
5.
____________ This substance inhibits prostaglandin H2 synthase-1 by blocking the channel
through which the substrate, arachidonate, travels.
Ans: f
Section: 12.4
Ans: b
Section: Introduction
Chapter 12 Membrane Structure and Function
2
6.
Cells maintain a __________ concentration of intracellular potassium as compared to the
extracellular concentration.
7.
____________ The type of amino acid found in the transmembrane helix of an integral protein.
Ans: i
Section: 12.3
8.
____________ This is the process by which lipids and proteins move in the membrane bilayer.
Ans: c
Section: 12.4
9.
____________ These membrane components contain carbohydrates.
Ans: a
Section: 12.1
10.
Ans: h
Section: 12.2
____________ This is a complex between cholesterol and membrane phospholipids.
Fill–in-the-Blank Questions
11.
is the noncovalent force that favors close packing of the tails of the lipids in a membrane.
Ans: van der Waals Section: 12.1
12.
are bilayer lipid vesicles with an aqueous compartment.
Ans: Liposomes Section: 12.1
13.
The of small molecules is correlated with their relative solubilities in water and non-polar
solvents.
Ans: permeability Section: 12.1
14.
Membranes are said to be because their two faces always differ from each other.
Ans: asymmetric Section: Introduction
15.
inserts into lipid bilayers, disrupting interactions between fatty acids, thereby helping to
maintain membrane fluidity.
Ans: Cholesterol Section: 12.2
16.
membrane proteins are bound primarily by electrostatic and hydrogen bond interactions with
the head groups of lipids.
Ans: k
Section: 12.5
Chapter 12 Membrane Structure and Function
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17.
Most cell membranes are electrically polarized, the inside being relative to the outside.
18.
The rate of lateral diffusion is such that a phospholipid molecule can travel from one end of a
bacterium to the other in of time.
Ans: one second Section: 12.4
19.
The temperature at which a phospholipid membrane transitions from a rigid to a fluid state is
referred to as .
Ans: Tm or melting temperature Section: 12.2
20.
An increase in the ratio of saturated to unsaturated fatty acid chains in a membrane the
fluidity of the membrane.
Ans: decreases Section: 12.2
Multiple-Choice Questions
21.
The energy for __________ transport comes from the gradient itself.
A)
active
B)
facilitated
C)
passive
D)
pumped
E)
ATP-mediated
Ans: C Section: 12.5
22.
Which of the following is true?
A)
Membranes are lipid bilayers.
B)
Membrane lipids have both hydrophobic and hydrophilic properties.
C)
Many membranes are electrically polarized.
D)
All of the above.
E)
None of the above.
Ans: D Section: Introduction
23.
How many molecules thick are membranes?
A)
two
B)
one
C)
infinite
D)
varying thickness, depending on structure
E)
None of the above.
Ans: A Section: Introduction
24.
Which of the following membranes would be the most fluid?
A)
a bilayer made of lipids with polyunsaturated 18 carbon-fatty acids
B)
a bilayer made of lipids with saturated 18 carbon-fatty acids
C)
a bilayer made of lipids with saturated 16 carbon-fatty acids
D)
a bilayer made of lipids with polyunsaturated 16 carbon-fatty acids
E)
All of the above are equivalent in fluidity.
Ans: D Section: 12.2
Ans: negative Section: Introduction
Chapter 12 Membrane Structure and Function
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25.
Which of the following statements is consistent with the structure of biological membranes?
A)
All membrane proteins are integral and associate with the hydrophobic region of the
membrane.
B)
Both proteins and lipids readily undergo transverse (“flip–flop”) diffusion from the inside
to the outside of the membrane.
C)
Membranes are symmetric.
D)
The membrane lipids self-assemble to form the lipid bilayer.
E)
A biological membrane consists of proteins sandwiched between two layers of lipids,
which is referred to as a lipid bilayer.
26.
Digitalis is a cardiotoinic steroid that does not act like a steroid. Instead its function is to
inhibit____________.
A)
the Na+-K+ pump
B)
fatty acid intake
C)
calcium channels
D)
potassium and sodium pores
E)
dropsy channel
Ans: A Section: 12.5
27.
An anti-porter and a symporter are examples of _____________.
A)
passive diffusion
B)
primary active transporters
C)
entropy driven pores
D)
an ABC transporter
E)
secondary transporter
Ans: E Section: 12.5
28.
Carbohydrate residues attached to the membrane lipids are
A)
always positioned on the intracellular side of the membrane.
B)
always positioned on the inside center of the bilayer.
C)
always positioned on the extracellular side of the membrane.
D)
always positioned equally on both sides of the membrane.
E)
also covalently attached to membrane proteins.
Ans: C Section: 11.1
29.
What force(s) stabilize(s) the lipid bilayers?
A)
van der Waals interactions
B)
electrostatic and hydrogen bonding between the polar heads and surrounding water
C)
covalent bonds between the lipid tails
D)
covalent bonds between the lipids and membrane proteins
E)
A and B
Ans: E Section: 12.1
Ans: D Section: 12.1
Chapter 12 Membrane Structure and Function
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30.
The degree of membrane fluidity depends on
A)
the percentage of lipids that contain choline.
B)
the percentage of glycolipids.
C)
the percentage of free fatty acids.
D)
the percentage of unsaturated fatty acids.
E)
None of the above.
31.
Which is the proper order of permeability of molecules across a membrane, from the most
permeable to the least?
A)
water, glucose, urea, sodium ion
D)
B)
water, indole, glucose, sodium ion
E)
C)
water, indole, sodium ion, glucose
Ans: B Section: 12.1
32.
The most common motif found in membrane spanning proteins is:
A)
helices of nonpolar amino acids that pass through the membrane.
B)
helices of charged amino acids that form channels via extensive hydrogen bonding.
C)
triple helix of helices.
D)
a helix-turn-helix arrangement of the peptide strands.
E)
None of the above.
Ans: A Section: 12.3
33.
The fluorescence recovery after photobleaching (FRAP) technique has been used to study:
A)
membrane composition.
B)
lateral diffusion in membranes.
C)
protein structural motifs in membranes.
D)
All of the above.
E)
None of the above.
Ans: B Section: 12.4
34.
The low incidence of protein or lipid flip-flop in a membrane preserves:
A)
membrane fluidity.
D)
B)
membrane melting temperatures.
E)
C)
membrane asymmetry.
Ans: C Section: 12.4
35.
Which of the following helps regulate membrane fluidity in animals?
A)
protein
D)
B)
cholesterol
E)
C)
ATP
Ans: B Section: 12.2
Ans: D Section: 12.2
Chapter 12 Membrane Structure and Function
6
36.
Which of the following describes the role of a protein in the selective permeability of a
membrane?
A)
The polar heads of phospholipids in allowing polar molecule to cross membranes.
B)
The binding of steroids to an extracellular peripheral membrane protein.
C)
The insertion of a porin with polar amino acids forming the β strands.
D)
Na+, K+-ATPase activity that sets up an electrical potential across the membrane.
E)
All of the above.
37.
Would you agree that a peripheral membrane protein can act as a Na+, K+-ATPase and why?
A)
Yes, because the Na+ and K+ is available intracellularly and extracellularly.
B)
Yes, because the hydrophobic amino side chains of the α helices firmly anchor the protein
to the membrane.
C)
No, because a peripheral protein does not form a transporter across the entire membrane.
D)
No, because only secondary active transport proteins can act as a Na+,K+-ATPase.
E)
No, because a P-glycoprotein must also be present for Na+, K+–ATPase activity.
Ans: C Section: 12.5
38.
What evidence exists to show that membrane asymmetry can be preserved for long periods?
A)
Lateral diffusion from fluorescence recovery after photo-bleaching experiments.
B)
Transverse diffusion of proteins has not been observed.
C)
Facilitated diffusion can take place in either direction depending on the concentration
gradient.
D)
Tumor cells often become resistant to drugs.
E)
The α helices in membrane-spanning proteins are hydrophobic and tightly packed.
Ans: B Section: 12.4
39.
If you wanted to study how membranes regulate their curvature and budding processes, which
of the following membrane structures would you study?
A)
presence of lipid rafts
B)
degree of fatty acid unsaturation
C)
presence of active transport proteins
D)
presence of prostaglandin H2 synthase-1
E)
None of the above.
Ans: A Section: 12.2
Short-Answer Questions
40.
Why are membranes impermeable to most substances?
Ans:
The hydrophobic core of the membrane makes crossing of polar molecules difficult due
to water associated with the compounds.
Section: 12.1
Ans: D Section: 12.3
Chapter 12 Membrane Structure and Function
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41.
How do proteins function to make membranes selectively permeable?
42.
What are the key biochemical elements for transmembrane spanning proteins?
forming core. The extracellular portion is typically glycosylated and is random ordered.
Section: 12.3
43.
Flip flopping of lipids takes place once in several hours. This is evidence for what?
membranes are able to achieve and hold asymmetry for a long period of time.
Section: 12.3
44.
Draw a cross-section of a membrane bilayer and a liposome.
of this.
Section: 12.1
45.
Describe a lipid raft and their potential role in a cell.
environment. These rafts are likely involved in cell-signaling events.
Section: 12.2
46.
How are lipid bilayers formed? What is the driving force?
each other by electrostatic and hydrogen-bonding attractions.
Section: 12.1
47.
Why do most phospholipids preferentially form sheets instead of micelles?
interior that acts as a mermeability barrier.
Section: 12.1
48.
What are liposomes? What are some of the current commercial applications?
creams.
Section: 12.1
mechanism to select for a single class or kind of molecule to allow through the cell.
Section: 12.5
Chapter 12 Membrane Structure and Function
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49.
Describe the effect of introducing a sodium ion pore into a membrane containing the Na+–
glucose symporter.
50.
Draw a bilayer membrane that has both an integral and peripheral protein present.
this.
Section: 12.3
51.
What is the function of prostaglandin H2 synthase-1? How does its position in the membrane
facilitate its activity?
enters the protein channel from within the membrane, successfully avoiding any
interaction with aqueous environments.
Section: 12.3
52.
What is multi-drug resistance?
Ans:
Cells may develop a resistance to drugs that were initially quite toxic to them. When this
occurs, they also develop resistance to a range of other compounds.
Section: 12.5
53.
Describe the selectivity of the potassium ion channel.
center. These residues point a carboxyl group inward, which binds potassium ions,
creating a selective filter for the K+ ions
Section: 12.5
54.
How do secondary transporters drive the transport of a substance up its concentration gradient?
Ans:
The thermodynamically uphill flow of one molecule is coupled to the downhill flow of
another.
Section: 12.5
55.
Why do defects in ABC transporters cause such serious health problems?
transporters usually involve a defect in an active transport system within an organ or cell
type.
Section: 12.5
without the transport of glucose. A secondary and devastating effect would be the loss of
Section: 12.5