Biol309
Question Bank
Membrane Structure
Multiple Choice
1. The fluidity of a membrane will decrease as a result of which one of the following changes?
A. increasing the average length of the fatty acids
B. increasing the number of double bonds in the fatty acids
C. decreasing the amount of cholesterol in the membrane
D. increasing the temperature of the membrane
2. Which one of the following statements correctly describes membrane structure?
A. Most membrane constituents are fixed in a specific location in the membrane.
B. The hydrophobic region of the membrane is located along the exposed outer surface.
C. Membranes consist of a ‘sandwich’ of lipids on the outside and protein on the inside.
D. Phospholipids are arranged with the fatty acids facing toward the center.
3. Which one of the following statements best describes phospholipid molecules?
A. They contain two fatty acids with an ester linkage to a glycerol residue.
B. Phospholipids of membranes always contain unsaturated fatty acids.
C. Phospholipids contain three fatty acid residues and a hydrophobic head group.
D. Along with triglycerides, phospholipids serve as important energy sources.
4. Which one of the following molecules is least likely to serve as a phospholipid’s head group?
A. choline
C. ribose
B. serine
D. ethanolamine
5. Which of these functions might be expected for a membrane protein?
A. serving as membrane receptors.
B. transport of substances across the membrane.
C. providing structure and support to the membrane.
D. All of the above are functions of membrane proteins.
6. The function of cholesterol would be best described as:
A. serving as hormone receptors.
B. modifying the fluidity of membranes.
C. facilitating the transport of lipids through the membrane.
D. causing arteriosclerosis and heart attacks
7. Considering membranes with phospholipids with these different average length fatty acids, which
one would be expected to display the highest fluidity?
A. 8 B.10 C.12 D.14
8. Considering membranes with phospholipids with fatty acids with these different average number
of double bonds, which one would be expected to display the highest fluidity?
A. 0 B.1
C.2
D.3
Biol 309
Question Bank
Membrane structure
Page 1
9. Molecules of the ____________ play the most important role in direct adhesion between cells.
A. Cell membrane
C. Cell cortex
B. Extracellular matrix
D. Cell wall
10. When dispersed into water, will each one of the following molecules form a
1) bilayer
2) micelle
3) insoluble droplet 4) or dissolve
Explain your answers.
A. triacylglycerol
B. acetone
C. sodium dodecyl sulfate
D. palmitic acid
11. Longer fatty acids make membranes less fluid because:
A. the long chains tend to get interwined and tangled.
B. this allows greater hydrogen-bonding between the methyl groups.
C. longer fatty acids bind rather tenaciously to membrane proteins.
D. there are more van derWaals interactions between the chains.
12. More double-bonds in fatty acids make membranes more fluid because:
A. fatty acids with lots of double bonds strongly repel each other.
B. the fatty acids cannot not pack together as tightly.
C. double bonds prevent cholesterol from entering the membrane.
D. the phospholipids tend to flip-flop across the membrane more quickly.
13. Why do glycolipids exist almost exclusively on the exterior side, but not the cytoplasmic side, of
the cell membrane?
A. The inner layer of the membrane is not thick enough to accommodate carbohydrates
B. Flippases move the glycolipids to this side of the membrane.
C. Carbohydrates are added only to lipids on the lumen side of the ER and golgi
membranes.
D. Carbohydrates are removed from the cytoplasmic side by glycosylase enzymes.
14. Does each of the following statements correctly describe the:
1) cell ‘cortex’
2) ‘extracellular matrix’
3) or both
A. This is the location of structural proteins that reinforce the cell membrane.
B. This region is rich in carbohydrate-containing macromolecules.
C. This region is the site of many enzymatic processes.
D. This layer provides anchor points for membrane proteins.
E. Molecules in this layer play an important role in cell-to-cell recognition.
F. This layer influences the shape of the cell.
G. This layer becomes hydrated and lubricates cell movement.
Biol 309
Question Bank
Membrane structure
Page 2
15. Which of the following membrane protein structures…
1) single pass alpha helix
2) 5x multipass alpha helix
…is most-likely to be found in a(n):
A. aqueous ion-channel
B) anchor protein
Explain your answers.
3) 18-strand beta-sheet
C) membrane receptor
16. A "tight junction":
A. is a special type membrane phospholipid molecule.
B. is the layer of protein and carbohydrate found between all cells.
C. restricts membrane proteins in the membrane to distinct domains.
D. resembles a small pore interconnecting two adjacent cells.
E. separates a cell from the external environment.
17. The experimental procedure known as "FRAP" can be used to demonstrate that:
A. cell membranes are composed of a bilayer of phospholipid molecules.
B. lipid molecules can "flip-flop" across the two sides of the lipid bilayer.
C. lipid and protein molecules move within a lipid bilayer.
D. membrane proteins transport specific molecules across the cell membrane.
True and False
1. The membrane of internal organelles consists of single layers (not a bilayer) of phospholipids.
2. The structures of most membrane proteins are now well known.
3. All membrane lipids are phospholipids.
4. In general, there is great diversity of oligosaccharide structures among glycoproteins and
glycolipids.
5. Increasing the cholesterol content of a lipid bilayer will decrease the fluidity of the membrane.
6. Most phospholipid synthesis occurs on the cytoplasmic side of the ER membrane.
7. After fusion with the cell membrane, the lumen side of a vesicle membrane will lie on the
cytoplasmic side of the cell membrane.
8. Weak detergents can be used to free proteins from membranes, but strong detergents will
completely denature the proteins.
Biol 309
Question Bank
Membrane structure
Page 3
Fill in, etc
1. Complete the following sentences using the word ‘hydrophobic’, ‘hydrophilic’ or ‘amphiphatic’.
The most amino acids of the transmembrane alpha-helix would be expected to have
__________________ side-chains. An ion passing through a mutipass transmembrane
protein would interact predominantly with ________________ amino acids. Membrane
proteins can be isolated from membranes with the use of __________________ molecules,
such as SDS or Triton X-100. Proteins associated with membranes through binding to other
proteins will have surface amino acids with _____________ side-chains.
2. Complete the following sentences.
The specialized properties of membranes is principally determined by the types of
____________________ incorporated into the membrane and the types of
____________________ on the phospholipids. Whereas the characteristics of the
phospholipid ____________________ significantly influence the fluidity of the membrane,
this is also affected by the amount of ______________________ embedded in the
membrane.
3. Complete this sentence.
Proteins that extend through a membrane are said to be ___________________, whereas
those that are non-covalently attached to the membrane surface are said to be
___________________.
4. Sometimes different membrane proteins in a small membrane domain move around in the cell
membrane, like ship-wrecked sailors sharing a raft in the ocean. If someone suggested to you that
this was due to anchoring of the proteins to the cell cortex, you would disagree since:
A. the cell cortex only binds to membrane lipids.
B. barriers created by tight-junctions offers a better explanation.
C. anchored proteins would show essentially no motion at all in the membrane.
D. binding to the cell cortex would not limit the movement of the proteins.
Recent analysis has shown that these membrane domains contain an unusually high concentration of
cholesterol. Explain how these so-called ‘cholesterol rafts’ could account for the observations
described above.
5. List and briefly describe 4 functions of membrane associated proteins.
1.
2.
3.
4.
Biol 309
Question Bank
Membrane structure
Page 4
6. The lipid composition on the two sides of the golgi membrane were determined with the following
results. Indicate whether each lipid requires the action of a flippase to achieve its final distribution.
Explain your answers.
Percent of total found in the:
Lipid
Cytoplasmic side
Lumen side
Phosphatidylcholine
2
98
Phosphatidylinositol
99
1
Phosphatidylserine
49
51
Digalactosyl-diacylglycerol 0
100
Requires
flipase (y/n)
_____
_____
_____
_____
Requires
scramblase (y/n)
_____
_____
_____
_____
If this golgi membrane were to pass through the vesicular transport pathway to the cell surface,
would the membrane surface on the exterior of the cell have the same composition as the
cytoplasmic or lumen side of the golgi membrane?
7. Thylakoid membranes typically are high in unsaturated phospholipids creating a highly fluid
membrane suitable for the functioning of the ATP synthase. In a recent study (Murakami et al,
2000, Science 287:476), the omega-3 fatty acid
desaturase was ‘knocked-out’ in two transgenic
(genetically engineered) tobacco lines. This
enzyme adds a third double bond to the fatty acids
of the membrane lipids (e.g., see Figure), and as a
result the transgenic plants showed a marked
decrease in the proportion of triene (triple
desaturated) fatty acids. The effect of this change
was examined in plants grown for 45 days at
different temperatures, with the following results
Plant growth (g fresh wt) after 45 days at:
Plant strain
15OC
25OC
30OC
37OC
T15 mutant
27%
6.2
489
492
124
T23 mutant
37%
6.9
513
445
123
Normal
82%
6.6
497
399
13
*% of digalactosyldiacylglycerol that has omega-3 double bond; the transgenic lines showed
reductions in triene fatty acids in other membrane lipids as well. Explain your answers to the
following questions:
A. Are the phospholipids of the transgenic plants more or less saturated than those of
normal plants?
B. Would the membranes of the transgenic plants be expected to be more or less fluid
than those of normal plants?
C. What significant difference in growth pattern do the transgenic plants display as
compared to the normal plants.
D. Does the observed change in plant growth at different temperatures correspond with the
expected effect of the mutation on membrane fluidity? Explain.
Triene
DiG-DAG*
Biol 309
Question Bank
Membrane structure
Page 5
8. This figure shows the results of a Fluorescence Recovery After Photobleaching (FRAP)
experiment of membrane lipids. The graph and photographs show the intensity of the photobleached
area before (Fi) and at different times (Fph0, Fph1, Fph2) following photobleaching
Appearance of
membrane
A. Why does the membrane fluoresce, and how was the spot shown in the ‘Fph0’created?
B. What does the curved line in the graph represent? The time required for the fluorescence
intensity to recover to the Fph2 level is a measure of what property of the membrane?
C. Suppose you were to rerun this experiment with a membrane with phospholipids that had
longer fatty acids. Draw another line on the graph to show the expected results after
Fo. Explain the difference.
9. What type of molecule is shown in this diagram?
Is it saturated or unsaturated? Why?
Label in the diagram the:
fatty acid tails
headgroup
glycerol
hydrophobic region
hydrophilic region
Biol 309
Question Bank
Membrane structure
Page 6