Some sample questions relating to membrane structure, transport, and
synthesis:
1.
To determine the effect of polar head group composition on the
fluidity of a phospholipid bilayer, a biologist performed the
following experiment. She made liposomes containing varying
proportions of phosphatidyl choline (PC) and phosphatidyl
ethanolamine (PE). The PC and PE used in the experment had
identical fatty acid chains (14 carbons long, completely saturated).
She analyzed the liposomes using differential scanning calorimetry.
The results of the experiments are shown in the graph below. The
percent values at the right of each curve represent the molar
percent of PC in the liposomes. The graph shows the results of
seven different experiments, using liposomes with 100% PC, 95%
PC, 90% PC, 80% PC, 50% PC, 20% PC, and 0% PC. (There is a
small peak at about 18C in the “100% PC” curve. It is an artifact.
Ignore it.)
Rate of
Heat Flow
(a)
Based on these results, what effect does varying the proportion of
PC and PE have on the fluidity of the lipid bilayer? Propose a
rationale for this effect, based on the differences in the structure of
the polar head groups of PC and PE. (5 pt)
(b)
The peak that is seen in the “50% PC” curve is wider than the
peaks seen at 100% PC and 0% PC. Briefly explain this. (5 pt)
Page 1
(c)
Predict the results that you would expect for differential scanning
calorimetric analysis of liposomes containing
34% PC: 34% PE: 32% cholesterol. In your prediction, I want you
to compare the results that you expect with the results seen in the
“50% PC” curve shown on the graph. Compare your prediction and
the “50% PC” curve with respect to the transition temperature and
the width of the transition peak. You may sketch a curve of your
prediction on the graph. (5 pt)
2.
Design an experiment to determine the location (exterior,
cytoplasmic, or transmembrane) of the carbohydrate on plasma
membrane integral proteins, using erythrocyte plasma membrane
as the experimental system. You may assume that you have a
reagent that tests specifically for carbohydrates. (10 pt)
3.
Fab fragments are antibody fragments containing the antigen
binding sites from the original antibody molecules. They are made
by treating antibody molecules with the proteolytic enzyme papain.
Each Fab fragment contains only one antigen binding site per
molecule.
(a)
In class, we talked about an experiment to demonstrate the lateral
mobility of integral membrane proteins by observing “patching and
capping” after treating cells with fluorecently labeled antibody.
What results do you predict should be seen if fluorescently-labeled
Fab fragments were used instead of whole antibody molecules in
the experiment? (5 pt)
(b)
Would this result (using Fab instead of whole antibody molecules)
support, contradict, or have no bearing on the conclusions that we
reached in class regarding lateral mobility in the patching and
capping experiment? Briefly explain. (5 pt)
Page 2
4.
You wish to study the activity of the voltage-gated K+ channel from
Drosophila cells (as shown in Fig. 4.36, pg 156). You have detected
the protein in plasma membranes from Drosophila salivary glands.
(a)
Your graduate advisor has suggested that you attempt to isolate
and reconstitute the activity of the K+ channel protein in a
liposome system. How would you do this? In your answer, be sure
to tell how you would get the protein out of the salivary gland
membranes and how you would put it into liposomes. Also (and
this is a critical part to the answer!), you must tell me how you will
know if the protein in the liposomes is working or not. Give as
much experimental detail as possible. (15 pt)
(b)
Assume that you were successful in part (a). In a separate set of
experiments, you found that if the liposomes in (a) were treated
briefly with trypsin, the K+ channel protein could still transport K+.
However, it was no longer sensitive to voltage changes across the
cell’s membrane. You found that K+ could go through the protein
no matter what the voltage across the membrane was! Briefly,
propose an explanation for this result. (5 pt)
5.
It is possible to make erythrocyte plasma membrane ghosts by
lysing erthrocytes in a hypotonic buffer. Under appropriate
conditions, the ghosts can be resealed to form closed vesicles. The
resealed ghosts retain the original orientation (“right-side-out”) of
the original plasma membrane, so that the outer leaflet of the
resealed ghost membrane is the same as the outer leaflet of the
erythrocyte plasma membrane. Before the ghosts are resealed,
they can be suspended in buffer containing different dissolved
substances; therefore, the experimenter can control precisely the
composition of the buffer inside the resealed ghost and outside the
resealed ghost.
The Na+-K+ pump is an integral membrane transport protein that
simultaneously transports Na+ out of the cell and K+ into the cell,
hydrolyzing ATP in the process. Therefore, this protein must have
a Na+ binding site, a K+ binding site, and an ATP binding site. In
a series of ghastly experiments on the erythrocyte Na+-K+ pump,
the following results were obtained. The ghosts were made in a
buffer with appropriate concentrations of Na+ and K+ to permit the
measurement of Na+-K+ pump activity. In the table, the “ATP” and
“oubain” columns tell whether or not the substance was present in
the buffer inside the ghosts or outside the ghosts. The last two
Page 3
columns tell whether or not the transport of Na+ and K+ was
observed.
Oubain is a chemical substance. It is pronounced “wah-bane.” It
does something.
Expt.
#
1
2
3
4
5
6
7
ATP present
inside
ghosts?
Yes
Yes
No
No
Yes
Yes
Yes
ATP present
outside
ghosts?
Yes
No
Yes
No
No
No
No
Oubain
present
inside
ghosts?
No
No
No
No
Yes
Yes
No
Oubain
present
outside
ghosts?
No
No
No
No
Yes
No
Yes
Results:
Was Na+
transported
?
Yes
Yes
No
No
Yes
Yes
Yes
Results:
Was K+
transported
?
Yes
Yes
No
No
No
Yes
No
(a)
What do these data suggest about the ATP binding and hydrolysis
site of the Na+-K+ pump? Briefly explain. (5 pt)
(b)
What is the action of oubain on the Na+-K+ pump? Do the data
suggest anything about the Na+ binding site? The K+ binding site?
If so, then briefly explain what the data suggest. (10 pt)
(c)
It is possible to alter the conditions during resealing to produce
inverted (“inside-out”) ghosts, in which the outside of the ghost is
the equivalent of the cytoplasmic face of the erythrocyte
membrane. If these experiments were repeated using inverted
ghosts, what results would you predict? (5 pt)
6.
Liposomes (made by mixing pure phospholipids in water) have
been used as artificial models of membrane structure and
properties. List the ways in which liposomes differ from the
membranes that occur in cells. (5 pt)
7.
Briefly, what information about membrane protein has been
learned in studies of the “purple membrane patches” of
Halobacterium halobium? Briefly explain the experimental
technique used in these studies, and tell why the Halobacterium
purple patches were especially suited to these studies. (5 pt)
8.
Briefly, what information about membrane protein has been
learned in photobleaching experiments using vertebrate retina rod
cells? (5 pt)
Page 4
9.
Briefly explain how to determine experimentally whether a
membrane protein is peripheral or integral, using electrophoresis
to visualize the protein. (5 pt)
10.
Compare and contrast the structures of sphingomyelin and
phosphatidylcholine. In your answer, relate the structures to the
roles of these substances in membranes. (5 pt)
1.
Imagine that you are using a togavirus model to study the
pathways of protein synthesis and transport. This model is ideal,
because you can grow the virus in cultured eukaryotic host cells.
Furthermore, the virus particles have only two proteins, a capsid
protein and an envelope protein. By using radiolabeled amino acids
in “pulse-chase” experiments, you established that the capsid
protein and envelope protein are synthesized via separate, distinct
paths.
CAPSID PROTEIN: Ribosome  Cytoplasm
ENVELOPE PROTEIN: Ribosome  Endoplasmic Reticulum 
Golgi Appartus  Plasma Membrane
Using genetic engineering techniques, you modified the viral RNA
as shown in the diagram below. You deleted a nucleotide sequence
located immediately in front of the coding region of the envelope
protein gene.
Capsid Protein
Gene
^
Site A
Envelope Protein
Gene
^
Site B
^
(1) Viral RNA before modification
Capsid Protein
Gene
^
Site A
Envelope Protein
Gene
^
Site B
(2) Genetically-modified Viral RNA: Note the deletion at site B
Page 5
The genetically-modified RNA was injected into host cells, where it
was able to begin the viral developmental cycle. However, no new
viral particles were produced by the modified RNA. Instead, both
the capsid and envelope protein remained localized in the
cytoplasm of the host cells.
USING MODIFIED RNA, BOTH CAPSID AND ENVELOPE PROTEIN:
Ribosome  Cytoplasm
(a)
pt)
Propose a hypothesis to explain the results of this experiment. (5
(b)
To test your hypothesis, you modify the viral RNA at site A. How
could you modify the RNA at site A in an experiment to test your
hypothesis? Be sure to tell me what results you predict from your
experiment. (5 pt)
2.
You are studying the process of protein synthesis on ribosomes
that are attached to the endoplasmic reticulum. As part of this
study, you have developed a reconstituted system for protein
synthesis on the ER, using microsomes. The system is as follows:

If you incubate (suspended in a buffered solution in a test
tube): ER microsomes, free ribosomes, some mRNA (specific for
the plasma membrane protein glycophorin), and appropriate
amino acids needed for protein synthesis – THE RIBOSOMES
CARRY OUT PROTEIN SYNTHESIS, BUT DO NOT BECOME
ATTACHED TO THE MICROSOMES.

If you incubate (suspended in a buffered solution in a test
tube): ER microsomes, free ribosomes, some mRNA (specific for
the plasma membrane protein glycophorin), appropriate amino
acids needed for protein synthesis, and a small amount of
freshly prepared cytosol– THE RIBOSOMES BECOME
ATTACHED TO THE MICROSOMES AND CARRY OUT PROTEIN
SYNTHESIS.

If you incubate (suspended in a buffered solution in a test
tube): ER microsomes, free ribosomes, some mRNA (specific for
the plasma membrane protein glycophorin), appropriate amino
acids needed for protein synthesis, and a small amount of
boiled cytosol (the cytosol was incubated at 100C for 20 min) –
THE RIBOSOMES CARRY OUT PROTEIN SYNTHESIS, BUT DO
NOT BECOME ATTACHED TO THE MICROSOMES.
Page 6
(a)
What are microsomes and cytosol, and how did you get them?
(10 pt)
(b)
Propose a hypothesis to explain the results of the experiment,
focusing on why the ribosomes either did or did not attach to the
microsomes.
(10 pt)
3.
An important experimental approach in studying protein
trafficking (and other cell processes) is the analysis of genetic
mutants in which the structure and activity of a specific protein is
altered or missing.
Below, I have listed several key components that regulate the
movement and sorting of proteins through the ER-Golgi pathway.
What I want you to do is this:


For each component, state its function or role in the protein
trafficking process.
What effect would you see in mutant cells in which the activity of the
component was completely lost? You must specifically state what
effects or changes would be observed in the mutant cells as compared
to the wild type. “The cell dies,” “It won’t work anymore,” or other
such statements are not acceptable answers.
Note that some components may have more than one function.
Also, you can assume that an appropriate experimental cell system
is available. These are worth 10 pt each.
For example:
N-acetylglucosamine phosphotransferase (in the cis Golgi):
This enzyme recognizes proteins that are destined to go to
lysosomes. It attaches two GlcNAc molecules to specific mannose
units in the N-linked carbohydrate core, through phosphate links.
A different enzyme removes the GlcNAc, leaving mannose
6-phosphate in the carbohydrate. Mannose 6-phosphate is the
sorting signal for lysosomal proteins. A receptor in the trans Golgi
apparatus binds to mannose 6-phosphate and sends the protein to
the lysosome.
In a mutant that is missing N-acetylglucosamine
phosphotransferase, the proteins that should go into the lysosomes
won’t go there anymore. One would predict two possible fates for
Page 7
this wrongly sorted protein: either it would accumulate in the trans
Golgi (most likely), or it would go into secretory vesicles and be
secreted.
(a)
phosphodiester glycosidase (in the cis Golgi)
(b)
clathrin
(c)
dolichol
(d)
COP I
(e)
syntaxin
(f)
Sar protein
(g)
translocon
16.
The following choices describe liposomes composed of glycerol-based
phospholipids. Which of the following liposomes will have the lowest
melting temperature, as determined by differential scanning calorimetry?
(You can assume that the head group and fatty acid chain length are the
same for each choice.)
(a)
(b)
(c)
(d)
(e)
Liposomes in which the fatty acid chains are fully saturated.
Liposomes with one cis double bond per fatty acid chain.
Liposomes with one trans double bond per fatty acid chain.
Liposomes with two cis double bonds per fatty acid chain.
Liposomes with two trans double bonds per fatty acid chain.
17.
A black membrane is
(a)
a phospholipid bilayer formed in a small hole in the partition between two
chambers.
a sealed vesicle formed by annealing the fragments of an erythrocyte
membrane.
an erythrocyte ghost.
an artificial bilayer in the form of of a spherical vesicle, formed by mixing
pure phospholipids in water.
a carbohydrate body that is covalently attached to the polar head groups
in the glycocalyx of the plasma membrane.
(b)
(c)
(d)
(e)
18.
Membranes from cells usually have an asymmetrical phospholipid
distribution. This means that the phospholipid composition of the
Page 8
outer leaflet of the membrane is different from the inner leaflet. How is
this asymmetry generated?
(a)
(b)
(c)
(d)
(e)
Phospholipid translocator enzymes in the endoplasmic reticulum move
specific phospholipid molecules from one leaflet to the other during the
synthesis of new lipid bilayer.
Certain phospholipid molecules (especially highly fluid ones, such as
those with unsaturated fatty acids) exhibit a substantially greater rate
of transverse mobility (“flip-flop”). These tend to move with greater
ease from the outer leaflet to the inner leaflet.
Certain phospholipid molecules (especially highly fluid ones, such as
those with unsaturated fatty acids) exhibit a substantially greater rate
of transverse mobility (“flip-flop”). These tend to move with greater
ease from the inner leaflet to the outer leaflet.
The lipids of the inner leaflet are synthesized in the endoplasmic
reticulum, and the lipids of the outer leaflet are synthesized in the
Golgi apparatus.
The lipids of the outer leaflet are synthesized in the endoplasmic
reticulum, and the lipids of the inner leaflet are synthesized in the
Golgi apparatus.
19.
In which part of a membrane would cholesterol be found?
(a)
(b)
(c)
(d)
(e)
Covalently attached to the polar head groups of the phospholipids.
Embedded in the fatty acid layer in the center of the lipid bilayer, with its
single –OH group in contact with a phospholipid head group layer.
Bound to peripheral protein molecules.
Attached to the cytoplasmic domain of integral membrane proteins.
Attached to carbohydrate groups in the glycocalyx.
20.
What role does cholesterol play in membrane structure and function?
(a)
(b)
(c)
It acts as a translocator to thread proteins through the membrane.
It acts as a channel to mediate ion transport.
It broadens the thermal transition temperature, thereby preventing rapid
phase transitions in the membrane.
It serves as a signal for protein sorting in the trans face of the Golgi
apparatus.
It is a major component of the glycocalyx.
(d)
(e)
21.
On which side of a plasma membrane is the greatest amount of
carbohydrate found?
(a)
(b)
No carbohydrate on either side of the plasma membrane.
A much greater amount of carbohydrate on the cytoplasmic (interior) side
of the erythrocyte plasma membrane.
Page 9
(c)
(d)
A much greater amount of carbohydrate on the exterior side of the
erythrocyte plasma membrane.
Approximately equal amounts of carbohydrate on the cytoplasmic and
exterior side.
22.
Which of the following statements best describes the action of the Na +-K+ATPase active transport pump?
(a)
The protein transports three Na+ into the cell and two K+ out of the cell,
hydrolyzing ATP in the process.
The protein transports three Na+ into the cell, two K+ out of the cell, and
two glucose molecules out of the cell, hydrolyzing ATP in the process.
The protein transports three Na+ out of the cell, and two K+ into the cell,
hydrolyzing ATP in the process.
The protein transports three Na+ out of the cell, two K+ into the cell, and
two glucose molecules into the cell, hydrolyzing ATP in the process.
(b)
(c)
(d)
Page 10
The following choices are used for questions 23 – 24. In each question, identify
the structure shown.
(a)
(b)
(c)
(d)
(e)
phosphatidyl choline
phosphatidyl ethanolamine
phosphatidyl serine
sphingomyelin
cholesterol
23.
24.
*******************************************************************************
The following choices are used for questions 25 – 27. Each choice refers to a
protein in the erythrocyte plasma membrane.
(a)
(b)
(c)
(d)
(e)
Band 3
Ankyrin
Spectrin
Band 4.1
Glycophorin
25.
This protein consists of two subunits,  and , that are twisted together. It
is attached to microfilaments on the cytoplasmic side of the erythrocyte
membrane.
26.
This protein is an integral protein in the erythrocyte plasma membrane,
with a single -helix forming the transmembrane domain. Its exact
function is unknown, although it may help to keep red blood cells from
clumping together during circulation.
27.
This protein is a multipass membrane protein that catalyzes the coupled
transport of Cl- and HCO3-.
**********************************************************************
Page 11
28.
In one experiment that we discussed in class, cells were used that
contained a light sensitive protein rhodopsin in their plasma membranes.
A small spot of the rhodopsin was photobleached with a laser light. Over a
short period of time, rhodopsin molecules from the area surrounding the
bleached spot were observed to move into the bleached spot. What did
this demonstrate?
Fluorescent light-driven pumping (active transport) of H+ across the
membrane.
(b)
A high rate of transverse mobility (flip-flop).
(c)
Polymerization of actin along the leading edge of the cell.
(d)
Glycosylation of the plasma membrane proteins
(e)
Lateral mobility (lateral diffusion) of the plasma membrane proteins.
*********************************************************************
The following choices are used for questions 29 - 32.
(a)
(a)
(b)
(c)
(d)
(e)
Simple diffusion directly across a phospholipid bilayer
Facilitated diffusion across a membrane
Active transport across a membrane
Both (a) and (b)
Both (b) and (c)
29.
Small hydrophobic and polar molecules (such as O2, CO2, N2, H2O, and
glycerol) can pass through a membrane by this mechanism, but larger
uncharged polar molecules and ions (such as glucose, Na+, and K+)
cannot pass through a membrane by this mechanism.
30.
A membrane protein must mediate this process.
31.
This process requires the expenditure of the cell’s energy, usually in the
form of ATP hydrolysis.
32.
In this process, the substance being transported moves from a high
concentration to a low concentration until equilibrium is reached.
**********************************************************************
33.
Membrane transport proteins that form hydrophilic pores through which
the solute (usually inorganic ions) can pass
(a)
(b)
(c)
(d)
(e)
are not found in neurons.
are carrier proteins.
always hydrolyze ATP in the process of transporting the solute.
are channel proteins.
are peripheral membrane proteins.
34.
A symport
Page 12
(a)
(b)
(c)
(d)
(e)
is a channel protein.
is a carrier protein that transports only a single type of solute.
is a carrier protein that transports two different solutes, each from the
same side of the membrane.
is a carrier protein that transports two different solutes, one from one side
of the membrane and one from the other side of the membrane.
is a synthetic carrier of ions (also known as an ionophore) useful as a
model for ion transport studies.
35.
In its resting state, the exterior of the plasma membrane of a neuron is
(a)
(b)
(c)
(d)
electrically neutral
positively charged
negatively charged
varies in its electrical charge, depending on whether it is a sensory, motor,
or associational
positively charged at the axons, and negatively charged at the dendrites.
(e)
36.
Proteins that are processed by the endoplasmic reticulum and Golgi
apparatus include
(a)
(b)
(c)
(d)
(e)
nuclear and mitochondrial proteins
integral plasma membrane proteins
proteins destined for secretion outside the cell
both (a) and (b)
both (b) and (c)
37.
Phagocytosis
(a)
is the endocytosis of small molecules and fluid, mediated by coated
pits.
is the uptake of bacteriophage by bacterial cells.
is the receptor-mediated endocytosis of large particles, such as the
“eating” of bacterial cells by certain leukocytes.
is the secretion of protein by receptor-mediated exocytosis.
is the secretion of protein by constitutive exocytosis.
(b)
(c)
(d)
(e)
Page 13
38.
Clathrin
(a)
(b)
(d)
(e)
mediates the import of proteins into the mitochondrion.
blocks the forward pathway of vesicular transport between the
endoplasmic reticulum and the Golgi apparatus.
forms a cage-like structure to aid in the formation and stability of coated
vesicles.
is the only protein to be associated with coated vesicles.
more than one of the above.
39.
A liposome is
(a)
a phospholipid bilayer formed in a small hole in the partition between
two chambers.
a sealed vesicle formed by annealing the fragments of an erythrocyte
membrane.
an erythrocyte ghost.
an artificial bilayer in the form of of a spherical vesicle, formed by
mixing pure phospholipids in water.
a carbohydrate body that is covalently attached to the polar head
groups in the glycocalyx of the plasma membrane.
(c)
(b)
(c)
(d)
(e)
**********************************************************************
The following information pertains to questions 40 through 42.
To determine the effect of polar head group composition on the fluidity of a
phospholipid bilayer, a biologist performed the following experiment. She
made liposomes containing varying proportions of phosphatidyl choline (PC)
and phosphatidyl ethanolamine (PE). The PC and PE used in the experment
had identical fatty acid chains (14 carbons long, completely saturated). She
analyzed the liposomes using differential scanning calorimetry. The results of
the experiments are shown in the graph below. The percent values at the
right of each curve represent the molar percent of PC in the liposomes. The
graph shows the results of seven different experiments, using liposomes with
100% PC, 95% PC, 90% PC, 80% PC, 50% PC, 20% PC, and 0% PC. (There is
a small peak at about 18C in the “100% PC” curve. It is an artifact. Ignore
it.)
Page 14
100%PC:0% PE
95% PC:5% PE
Rate of
Heat Flow
90% PC:10% PE
80% PC: 20% PE
50% PC: 50% PE
20% PC: 80% PE
0% PC: 100% PE
Temperature (C)
40.
What effect does varying the proportion of PC and PE have on the lipid
bilayer?
(a)
(b)
The proportion of PC and PE has no effect on the bilayer fluidity.
Increasing the percentage of PC increases the fluidity (and decreases
the melting temperature) of the bilayer.
Increasing the percentage of PE increases the fluidity (and decreases
the melting temperature) of the bilayer.
Increasing the percentage of PC increases the amount of cholesterol in
the bilayer.
Increasing the percentage of PC increases the amount of
sphingomyelin in the bilayer.
(c)
(d)
(e)
41.
Which of the following best explains the effect of varying the PC:PE
ratio?
(a)
The PC has a greater number of double bonds in its fatty acid
structure than PE.
The PC has a greater number of fatty acid chains in its structure than
PE.
The PC has a larger polar head group structure than PE.
The PC has a greater amount of cholesterol in its structure than PE.
The PC has a greater amount of sphingomyelin in its structure than
PE.
(b)
(c)
(d)
(e)
Page 15
42.
The peak that is seen in the “50% PC” curve is wider than the peaks
seen at 100% PC and 0% PC. Which of the following is the most likely
explanation for this?
(a)
The packing of the phospholipid molecules is more irregular in the
“50% PC” liposomes. Therefore, the structure is less crystalline, more
amorphous, and has a broader phase transition temperature.
In the “50% PC” liposomes, all of the PC is located in the outer leaflet
of the bilayer, and all of the PE is located in the inner leaflet.
Therefore, the outer leaflet melts first, giving an overall broader phase
transition temperature.
The packing of the phospholipid molecules is more regular in the “50%
PC” liposomes. Therefore, the structure is more crystalline, less
amorphous, and has a broader phase transition temperature.
In the “50% PC” liposomes, all of the PE is located in the outer leaflet
of the bilayer, and all of the PC is located in the inner leaflet.
Therefore, the inner leaflet melts first, giving an overall broader phase
transition temperature.
(b)
(c)
(d)
**********************************************************************
43.
In the transcellular transport of glucose across an intestinal epithelial
cell, glucose is transported from a low concentration in the lumen of
the intestine to a high concentration in the cytoplasm of the intestinal
epithelial cell. The energy required for this process is provided
(a)
(b)
(c)
(d)
by the natural kinetic energy in the diffusion of the glucose molecules.
by the hydrolysis of ATP, accomplished by the Na+-glucose ATPase
located at the lumenal face of the epithelial cells.
by the glycolytic breakdown of the glucose as it crosses the epithelial
cell plasma membrane.
by the co-transport of Na+ from a high [Na+] in the lumen of the
intestine to a low [Na+] in the cytoplasm of the intestinal epithelial
cell, accomplished by the Na+-glucose symport located at the lumenal
face of the epithelial cells.
Page 16
44.
Which of the following best describes the events of a “nerve impulse” in
a neuron?
(a)
An electrical signal, in the form of a stream of electrons, is transmitted
across conductor molecules bound to carbohydrates in the glycocalyx of
the membrane.
The action of the Na+-K+-ATPase is reversed, causing it to pump Na+
into the cell and K+ out of the cell. This causes a small section of the
neuron membrane to be briefly depolarized, an effect which is
propagated along the length of the neuron in a “wave” of
depolarization.
A voltage-gated K+-channel is opened, resulting in a rush of K+ from
the outside of the cell to the inside of the cell. This causes a small
section of the neuron membrane to be briefly depolarized, an effect
which is propagated along the length of the neuron in a “wave” of
depolarization.
A voltage-gated Na+-channel is opened, resulting in a rush of Na+ from
the outside of the cell to the inside of the cell. This causes a small
section of the neuron membrane to be briefly depolarized, an effect
which is propagated along the length of the neuron in a “wave” of
depolarization.
A ligand-gated (neurotransmitter-gated) K+-channel is opened,
resulting in a rush of K+ from the outside of the cell to the inside of the
cell. This causes a small section of the neuron membrane to be briefly
depolarized, an effect which is propagated along the length of the
neuron in a “wave” of depolarization.
(b)
(c)
(d)
(e)
**********************************************************************
The following choices are used for questions 45 – 49. For each question,
indicate where the process takes place.
(a)
(b)
(c)
(d)
Endoplasmic reticulum
Cis region of the Golgi apparatus
Medial region of the Golgi apparatus
Trans region of the Golgi apparatus
45.
Sorting of proteins into lysosomes and secretory vesicles
46.
Attachment of N-linked oligosaccharide to glycoprotein
47.
Insertion of a transmembrane domain of an integral membrane protein
48.
Binding of a signal-recognition particle to an SRP receptor protein
49.
Phosphorylation of oligosaccharides on lysosomal proteins
Page 17
50.
What is the function of lysosomes?
(a)
They transport membrane from the Golgi apparatus to the plasma
membrane.
They mediate the active transport of ions.
They return ER-resident proteins back to endoplasmic reticulum.
They contain acid hydrolases to hydrolyze substances brought into the
cell by endocytosis.
They modify the N-linked oligosaccharide of glycoproteins.
(b)
(c)
(d)
(e)
Page 18