Final Exam Question Bank Chapter 15 - Intracellular Compartments | Môn Biology - Trường Đại học Quốc tế, Đại học Quốc gia Thành phố Hồ Chí Minh

lOMoAR cPSD| 59078336
ESSENTIAL CELL BIOLOGY, FOURTH EDITION
CHAPTER 15: INTRACELLULAR COMPARTMENTS AND PROTEIN TRANSPORT
© 2014 GARLAND SCIENCE PUBLISHING
Membrane-Enclosed Organelles
15-1 Which of the following statements about the endoplasmic reticulum (ER) is false? (a)
The ER is the major site for new membrane synthesis in the cell. (b)
Proteins to be delivered to the ER lumen are synthesized on smooth ER. (c)
Steroid hormones are synthesized on the smooth ER. (d)
The ER membrane is contiguous with the outer nuclear membrane.
15-2 Which of the following statements about membrane-enclosed organelles is true? (a)
In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane. (b)
The nucleus is the only organelle that is surrounded by a double membrane. (c)
Other than the nucleus, most organelles are small and thus, in a typical cell, only
about 10% of a cell’s volume is occupied by membrane-enclosed organelles; the
other 90% of the cell volume is the cytosol. (d)
The nucleus is the only organelle that contains DNA.
15-3 Name the membrane-enclosed compartments in a eukaryotic cell where each of the
functions listed below takes place. A. photosynthesis B. transcription C. oxidative phosphorylation D.
modification of secreted proteins E. steroid hormone synthesis F.
degradation of worn-out organelles G. new membrane synthesis H.
breakdown of lipids and toxic molecules
15-4 Label the structures of the cell indicated by the lines in Figure Q15-4. lOMoAR cPSD| 59078336 Figure Q15-4 A. nucleus B. peroxisome C. rough endoplasmic reticulum D. Golgi apparatus E. cytosol F. endosome G. plasma membrane H. lysosome I. mitochondrion J. smooth endoplasmic reticulum
15-5 For each of the following sentences, fill in the blanks with the best word or phrase selected
from the list below. Not all words or phrases will be used; use each word or phrase only once.
The __________________ makes up about half of the total cell volume of a typical
eukaryotic cell. Ingested materials within the cell will pass through a series of
compartments called __________________ on their way to the __________________,
which contains digestive enzymes and will ultimately degrade the particles and
macromolecules taken into the cell and will also degrade worn-out organelles. The
__________________ has a cis and trans face and receives proteins and lipids from the
__________________, a system of interconnected sacs and tubes of membranes that
typically extends throughout the cell. cytosol Golgi apparatus nucleus endoplasmic reticulum lysosome peroxisomes endosomes mitochondria plasma membrane lOMoAR cPSD| 59078336
15-6 Which of the following organelles is not part of the endomembrane system? (a) Golgi apparatus (b) the nucleus (c) mitochondria (d) lysosomes
15-7 You discover a fungus that contains a strange star-shaped organelle not found in any other
eukaryotic cell you have seen. On further investigation, you find the following. 1.
The organelle possesses a small genome in its interior. 2.
The organelle is surrounded by two membranes. 3.
Vesicles do not pinch off from the organelle membrane. 4.
The interior of the organelle contains proteins similar to those of many bacteria. 5.
The interior of the organelle contains ribosomes.
How might this organelle have arisen?
15-8 Which of the following statements is true? (a)
Lysosomes are believed to have originated from the engulfment of bacteria specialized for digestion. (b)
The nuclear membrane is thought to have arisen from the plasma membrane invaginating around the DNA. (c)
Because bacteria do not have mitochondria, they cannot produce ATP in a membrane-dependent fashion. (d)
Chloroplasts and mitochondria share their DNA. Protein Sorting
15-9 For each of the following sentences, fill in the blanks with the best word or phrase selected
from the list below. Not all words or phrases will be used; use each word or phrase only once.
Plasma membrane proteins are inserted into the membrane in the __________________.
The address information for protein sorting in a eukaryotic cell is contained in the
__________________ of the proteins. Proteins enter the nucleus in their
__________________ form. Proteins that remain in the cytosol do not contain a
__________________. Proteins are transported into the Golgi apparatus via
__________________. The proteins transported into the endoplasmic reticulum by
__________________ are in their __________________ form. amino acid sequence Golgi apparatus sorting signal endoplasmic reticulum plasma membrane transport vesicles folded protein translocators unfolded lOMoAR cPSD| 59078336
15-10 Where are proteins in the chloroplast synthesized? (a) in the cytosol (b) in the chloroplast (c) on the endoplasmic reticulum (d)
in both the cytosol and the chloroplast
15-11 Proteins that are fully translated in the cytosol do not end up in _______. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) transport vesicles.
15-12 Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) the nuclear membrane.
15-13 Signal sequences that direct proteins to the correct compartment are _________. (a)
added to proteins through post-translational modification. (b)
added to a protein by a protein translocator. (c)
encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination. (d)
always removed once a protein is at the correct destination.
15-14 What is the role of the nuclear localization sequence in a nuclear protein? (a)
It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. (b)
It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. (c)
It aids in protein unfolding so that the protein can thread through nuclear pores. (d)
It prevents the protein from diffusing out of the nucleus through nuclear pores.
15-15 Which of the following statements about nuclear transport is true? (a)
mRNAs and proteins transit the nucleus through different types of nuclear pores. (b)
Nuclear import receptors bind to proteins in the cytosol and bring the proteins to
the nuclear pores, where the proteins are released from the receptors into the pores for transit into the nucleus. (c)
Nuclear pores have water-filled passages that small, water-soluble molecules can
pass through in a nonselective fashion. (d)
Nuclear pores are made up of many copies of a single protein. lOMoAR cPSD| 59078336
15-16 A large protein that passes through the nuclear pore must have an appropriate _________. (a)
sorting sequence, which typically contains the positively charged amino acids lysine and arginine. (b)
sorting sequence, which typically contains the hydrophobic amino acids leucine and isoleucine. (c)
sequence to interact with the nuclear fibrils. (d)
Ran-interacting protein domain.
15-17 A gene regulatory protein, A, contains a typical nuclear localization signal but surprisingly
is usually found in the cytosol. When the cell is exposed to hormones, protein A moves
from the cytosol into the nucleus, where it turns on genes involved in cell division. When
you purify protein A from cells that have not been treated with hormones, you find that
protein B is always complexed with it. To determine the function of protein B, you
engineer cells lacking the gene for protein B. You compare normal and defective cells by
using differential centrifugation to separate the nuclear fraction from the cytoplasmic
fraction, and then separating the proteins in these fractions by gel electrophoresis. You
identify the presence of protein A and protein B by looking for their characteristic bands
on the gel. The gel you run is shown in Figure Q15-17. Figure Q15-17
On the basis of these results, what is the function of protein B? Explain your conclusion
and propose a mechanism for how protein B works.
15-18 Your friend works in a biotechnology company and has discovered a drug that blocks the
ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport? (a)
Nuclear transport receptors would be unable to bind cargo. (b)
Nuclear transport receptors would be unable to enter the nucleus. (c)
Nuclear transport receptors would be unable to release their cargo in the nucleus. (d)
Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils.
15-19 Which of the following statements is true? lOMoAR cPSD| 59078336 (a)
The signal sequences on mitochondrial proteins are usually at the C-terminus. (b)
Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria. (c)
Chaperone proteins in the mitochondria facilitate the movement of proteins across
the outer and inner mitochondrial membranes. (d)
Mitochondrial proteins cross the membrane in their native, folded state.
15-20 Which of the following statements about transport into mitochondria and chloroplasts is false? (a)
The signal sequence on proteins destined for these organelles is recognized by a
receptor protein in the outer membrane of these organelles. (b)
After a protein moves through the protein translocator in the outer membrane of
these organelles, the protein diffuses in the lumen until it encounters a protein
translocator in the inner membrane. (c)
Proteins that are transported into these organelles are unfolded as they are being transported. (d)
Signal peptidase will remove the signal sequence once the protein has been
imported into these organelles.
15-21 Which of the following statements about peroxisomes is false? (a)
Most peroxisomal proteins are synthesized in the ER. (b)
Peroxisomes synthesize phospholipids for the myelin sheath. (c)
Peroxisomes produce hydrogen peroxide. (d)
Vesicles that bud from the ER can mature into peroxisomes.
15-22 You are trying to identify the peroxisome-targeting sequence in the thiolase enzyme in
yeast. The thiolase enzyme normally resides in the peroxisome and therefore must contain
amino acid sequences that are used to target the enzyme for import into the peroxisome.
To identify the targeting sequences, you create a set of hybrid genes that encode fusion
proteins containing part of the thiolase protein fused to another protein, histidinol
dehydrogenase (HDH). HDH is a cytosolic enzyme required for the synthesis of the amino
acid histidine and cannot function if it is localized in the peroxisome. You genetically
engineer a series of yeast cells to express these fusion proteins instead of their own
versions of these enzymes. If the fusion proteins are imported into the peroxisome, the
HDH portion of the protein cannot function and the yeast cells cannot grow on a medium
lacking histidine. You obtain the results shown in Figure Q15-22. lOMoAR cPSD| 59078336 Figure Q15-22
What region of the thiolase protein contains the peroxisomal targeting sequence? Explain your answer.
15-23 Most proteins destined to enter the endoplasmic reticulum _________. (a)
are transported across the membrane after their synthesis is complete. (b)
are synthesized on free ribosomes in the cytosol. (c)
begin to cross the membrane while still being synthesized. (d) remain within the endoplasmic reticulum.
15-24 After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify
the RNAs attached to it. Which of the following proteins do you expect the RNA from the
rough endoplasmic reticulum to encode? (a) soluble secreted proteins (b) ER membrane proteins (c) plasma membrane proteins (d) all of the above
15-25 In which cellular location would you expect to find ribosomes translating mRNAs that
encode ribosomal proteins? (a) the nucleus (b) on the rough ER (c) in the cytosol (d) in the lumen of the ER
15-26 What would happen in each of the following cases? Assume in each case that the protein
involved is a soluble protein, not a membrane protein. lOMoAR cPSD| 59078336 A.
You add a signal sequence (for the ER) to the N-terminal end of a normally cytosolic protein. B.
You change the hydrophobic amino acids in an ER signal sequence into charged amino acids. C.
You change the hydrophobic amino acids in an ER signal sequence into other hydrophobic amino acids. D.
You move the N-terminal ER signal sequence to the C-terminal end of the protein.
15-27 You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given
that information, which of the following statements must be true? (a)
Fuzzy has a C-terminal signal sequence that binds to SRP. (b)
Only one ribosome can be bound to the mRNA encoding Fuzzy during translation. (c)
Fuzzy must contain a hydrophobic stop-transfer sequence. (d)
Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be
ejected into the ER membrane and degraded.
15-28 Which of the following statements about a protein in the lumen of the ER is false? (a)
A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane. (b)
Some of the proteins in the lumen of the ER can end up in the extracellular space. (c)
Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system. (d)
Some of the proteins in the lumen of the ER can end up in the plasma membrane.
15-29 Which of the following statements is true? (a)
Proteins destined for the ER are translated by a special pool of ribosomes whose
subunits are always associated with the outer ER membrane. (b)
Proteins destined for the ER translocate their associated mRNAs into the ER lumen where they are translated. (c)
Proteins destined for the ER are translated by cytosolic ribosomes and are targeted
to the ER when a signal sequence emerges during translation. (d)
Proteins destined for the ER are translated by a pool of cytosolic ribosomes that
contain ER-targeting sequences that interact with ER-associated protein translocators.
15-30 Match the components involved with ER transport with the appropriate cellular location.
Locations can be used more than once, or not at all. Components Location
1. signal-recognition particle _____ A. cytosol 2. protein translocator _____ B. ER lumen 3. mRNA _____ C. ER membrane 4. SRP receptor _____
5. active site of signal peptidase ____ lOMoAR cPSD| 59078336
15-31 Figure Q15-31 shows the organization of a protein that resides on the ER membrane. The
N- and C-termini of the protein are labeled. Boxes 1, 2, and 3 represent membranespanning
sequences. Non-membrane-spanning regions of the protein are labeled “X,” “Y,” and “Z.” Figure Q15-31
Once this protein is fully translocated, where will region Y be? (a) in the cytoplasm (b) in the ER lumen (c) inserted into the ER membrane (d) degraded by signal peptidase
15-32 Briefly describe the mechanism by which an internal stop-transfer sequence in a protein
causes the protein to become embedded in the lipid bilayer as a transmembrane protein
with a single membrane-spanning region. Assume that the protein has an N-terminal
signal sequence and just one internal hydrophobic stop-transfer sequence.
15-33 Using genetic engineering techniques, you have created a set of proteins that contain two
(and only two) conflicting signal sequences that specify different compartments. Predict
which signal would win out for the following combinations. Explain your answers. A.
Signals for import into the nucleus and import into the ER. B.
Signals for export from the nucleus and import into the mitochondria. C.
Signals for import into mitochondria and retention in the ER.
15-34 Figure Q15-34 shows the organization of a protein that normally resides in the plasma
membrane. The boxes labeled 1 and 2 represent membrane-spanning sequences and the
arrow represents a site of action of signal peptidase. Given this diagram, which of the
following statements must be true? Figure Q15-34 (a)
The N-terminus of this protein is cytoplasmic. (b)
The C-terminus of this protein is cytoplasmic. (c)
The mature version of this protein will span the membrane twice, with both the N-
and C-terminus in the cytoplasm. (d) None of the above. lOMoAR cPSD| 59078336
15-35 Figure Q15-35 shows the orientation of a multipass transmembrane protein after it has
completed its entry into the ER membrane (part A) and after it gets delivered to the plasma
membrane (part B). This protein has an N-terminal signal sequence (depicted as the dark
gray membrane-spanning box), which signal peptidase cleaves off in the endoplasmic
reticulum. The other membrane-spanning domains in the protein are represented as open
boxes. Given that any hydrophobic membrane-spanning domain can act as either a start-
transfer region or a stop-transfer region, draw the final consequences of the actions
described below on the orientation of the protein in the plasma membrane. Indicate on
your drawing the extracellular space, the cytosolic face, and the plasma membrane, as well
as the N- and C-terminus of the protein. Figure Q15-35 A.
deleting the first signal sequence B.
changing the hydrophobic amino acids in the first, cleaved sequence to charged amino acids C.
changing the hydrophobic residues in every other transmembrane sequence to
charged residues, starting with the first, cleaved signal sequence Vesicular Transport
15-36 Which of the following choices reflects the appropriate order of locations through which a
protein destined for the plasma membrane travels? (a)
lysosome → endosome → plasma membrane (b)
ER → lysosome → plasma membrane (c)
Golgi → lysosome → plasma membrane (d)
ER → Golgi → plasma membrane
15-37 For each of the following sentences, fill in the blanks with the best word or phrase selected
from the list below. Not all words or phrases will be used; use each word or phrase only once.
Proteins are transported out of a cell via the __________________ or
__________________ pathway. Fluids and macromolecules are transported into the cell
via the __________________ pathway. All proteins being transported out of the cell pass lOMoAR cPSD| 59078336
through the __________________ and the __________________. Transport vesicles link
organelles of the __________________ system. The formation of __________________
in the endoplasmic reticulum stabilizes protein structure. carbohydrate Golgi apparatus disulfide bonds hydrogen bonds endocytic ionic bonds endomembrane lysosome endoplasmic reticulum protein endosome secretory exocytic
15-38 Which of the following statements about vesicle budding from the Golgi is false? (a)
Clathrin molecules are important for binding to and selecting cargoes for transport. (b)
Adaptins interact with clathrin. (c)
Once vesicle budding occurs, clathrin molecules are released from the vesicle. (d)
Clathrin molecules act at the cytosolic surface of the Golgi membrane.
15-39 Molecules to be packaged into vesicles for transport are selected by ________. (a) clathrin. (b) adaptins. (c) dynamin. lOMoAR cPSD| 59078336 (d) SNAREs.
15-40 Which of the following protein families are not involved in directing transport vesicles to the target membrane? (a) SNAREs (b) Rabs (c) tethering proteins (d) adaptins
15-41 Your friend has just joined a lab that studies vesicle budding from the Golgi and has been
given a cell line that does not form mature vesicles. He wants to start designing some
experiments but wasn’t listening carefully when he was told about the molecular defect of
this cell line. He’s too embarrassed to ask and comes to you for help. He does recall that
this cell line forms coated pits but vesicle budding and the removal of coat proteins don’t
happen. Which of the following proteins might be lacking in this cell line? (a) clathrin (b) Rab (c) dynamin (d) adaptin
15-42 An individual transport vesicle ________. (a)
contains only one type of protein in its lumen. (b)
will fuse with only one type of membrane. (c)
is endocytic if it is traveling toward the plasma membrane. (d)
is enclosed by a membrane with the same lipid and protein composition as the
membrane of the donor organelle.
15-43 Which of the following statements about vesicular membrane fusion is false? (a)
Membrane fusion does not always immediately follow vesicle docking. (b)
The hydrophilic surfaces of membranes have water molecules associated with them
that must be displaced before vesicle fusion can occur. (c)
The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion. (d)
The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane
and the target organelle membrane together so that their lipids can intermix.
15-44 v-SNAREs and t-SNAREs mediate the recognition of a vesicle at its target membrane so
that a vesicle displaying a particular type of v-SNARE will only fuse with a target
membrane containing a complementary type of t-SNARE. In some cases, v-SNAREs and
t-SNAREs may also mediate the fusion of identical membranes. In yeast cells, right before
the formation of a new cell, vesicles derived from the vacuole will come together and fuse
to form a new vacuole destined for the new cell. Unlike the situation we have discussed in
class, the vacuolar vesicles contain both v-SNAREs and t-SNAREs. Your friend is trying
to understand the role of these SNAREs in the formation of the new vacuole and consults
with you regarding the interpretation of his data. lOMoAR cPSD| 59078336
Your friend has designed an ingenious assay for the fusion of vacuolar vesicles by using
alkaline phosphatase. The protein alkaline phosphatase is made in a “pro” form that must
be cleaved for the protein to be active. Your friend has designed two different strains of
yeast: strain A produces the “pro” form of alkaline phosphatase (pro-Pase), whereas strain
B produces the protease that can cleave pro-Pase into the active form (Pase). Neither strain
has the active form of the alkaline phosphatase, but when vacuolar vesicles from the strains
A and B are mixed, fusion of vesicles generates active alkaline phosphatase, whose activity
can be measured and quantified (Figure Q15-44A). Figure Q15-44
Your friend has taken each of these yeast strains and further engineered them so that they
express only the v-SNAREs, only the t-SNAREs, both SNAREs (the normal situation), or
neither SNARE. He then isolates vacuolar vesicles from all strains and tests the ability of
each variant form of strain A to fuse with each variant form of strain B, by using the alkaline
phosphatase assay. The data are shown in the graph in Figure Q15-44B. On this graph, the
SNARE present on the vesicle of the particular yeast strain is indicated as “v” (for the
presence of the v-SNARE) and “t” (for the presence of the t-SNARE).
What do his data say about the requirements for v-SNAREs and t-SNAREs in the vacuolar
vesicles? Is it important to have a specific type of SNARE (that is, v-SNARE or t-SNARE) on each vesicle? Secretory Pathways
15-45 N-linked oligosaccharides on secreted glycoproteins are attached to ________. (a)
nitrogen atoms in the polypeptide backbone. (b)
the serine or threonine in the sequence Asn-X-Ser/Thr. (c)
the N-terminus of the protein. lOMoAR cPSD| 59078336 (d)
the asparagine in the sequence Asn-X-Ser/Thr.
15-46 Name two types of protein modification that can occur in the ER but not in the cytosol. 15-
47 Which of the following statements about disulfide bond formation is false? (a)
Disulfide bonds do not form under reducing environments. (b)
Disulfide bonding occurs by the oxidation of pairs of cysteine side chains on the protein. (c)
Disulfide bonding stabilizes the structure of proteins. (d)
Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing.
15-48 Cells have oligosaccharides displayed on their cell surface that are important for cell–cell
recognition. Your friend discovered a transmembrane glycoprotein, GP1, on a pathogenic
yeast cell that is recognized by human immune cells. He decides to purify large amounts
of GP1 by expressing it in bacteria. To his purified protein he then adds a branched 14sugar
oligosaccharide to the asparagine of the only Asn-X-Ser sequence found on GP1 (Figure
Q15-48). Unfortunately, immune cells do not seem to recognize this synthesized
glycoprotein. Which of the following statements is a likely explanation for this problem? Figure Q15-48 (a)
The oligosaccharide should have been added to the serine instead of the asparagine. (b)
The oligosaccharide should have been added one sugar at a time. (c)
The oligosaccharide needs to be further modified before it is mature. (d) The
oligosaccharide needs a disulfide bond.
15-49 Different glycoproteins can have a diverse array of oligosaccharides. Which of the
statements below about this diversity is true? lOMoAR cPSD| 59078336 (a)
Extensive modification of oligosaccharides occurs in the extracellular space. (b)
Different oligosaccharides are covalently linked to proteins in the ER and the Golgi. (c)
A diversity of oligosaccharyl transferases recognizes specific protein sequences,
resulting in the linkage of a variety of oligosaccharides to proteins. (d)
Oligosaccharide diversity comes from modifications that occur in the ER and the
Golgi of the 14-sugar oligosaccharide added to the protein in the ER.
15-50 If you remove the ER retention signal from a protein that normally resides in the ER lumen,
where do you predict the protein will ultimately end up? Explain your reasoning.
15-51 Which of the following statements about the protein quality control system in the ER is false? (a)
Chaperone proteins help misfolded proteins fold properly. (b)
Proteins that are misfolded are degraded in the ER lumen. (c)
Protein complexes are checked for proper assembly before they can exit the ER. (d)
A chaperone protein will bind to a misfolded protein to retain it in the ER.
15-52 Which of the following statements about the unfolded protein response (UPR) is false? (a)
Activation of the UPR results in the production of more ER membrane. (b)
Activation of the UPR results in the production of more chaperone proteins. (c)
Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins. (d)
Activation of the UPR results in the cytoplasmic activation of gene regulatory proteins.
15-53 Match the set of labels below with the numbered label lines on Figure Q15-53. Figure Q15-53 A. cisterna B.
Golgi stack C. secretory vesicle lOMoAR cPSD| 59078336 D. trans Golgi network E. cis Golgi network
15-54 Vesicles from the ER enter the Golgi at the ______. (a) medial cisternae. (b) trans Golgi network. (c) cis Golgi network. (d) trans cisternae.
15-55 A plasma membrane protein carries an oligosaccharide containing mannose (Man),
galactose (Gal), sialic acid (SA), and N-acetylglucosamine (GlcNAc). These sugars are
added to the protein as it proceeds through the secretory pathway. First, a core
oligosaccharide containing Man and GlcNAc is added, followed by Gal, Man, SA, and
GlcNAc in a particular order. Each addition is catalyzed by a different transferase acting at
a different stage as the protein proceeds through the secretory pathway. You have isolated
mutants defective for each of the transferases, purified the membrane protein from each of
the mutants, and identified which sugars are present in each mutant protein. Table Q15-55 summarizes the results. Table Q15-55
From these results, match each of the transferases (A, B, C, D) to its subcellular location
selected from the list below. (Assume that each location contains only one enzyme.) 1. central Golgi cisternae 2. cis Golgi network 3. ER 4. trans Golgi network
15-56 Which of the following statements about secretion is true? (a)
The membrane of a secretory vesicle will fuse with the plasma membrane when it
discharges its contents to the cell’s exterior. (b)
Vesicles for regulated exocytosis will not bud off the trans Golgi network until the
appropriate signal has been received by the cell. (c)
The signal sequences of proteins destined for constitutive exocytosis ensure their
packaging into the correct vesicles. lOMoAR cPSD| 59078336 (d)
Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH
of the trans Golgi network.
15-57 Figure Q15-57 shows the orientation of the Krt1 protein on the membrane of a Golgiderived
vesicle that will fuse with the plasma membrane. Figure Q15-57
Given this diagram, which of the following statements is true? (a)
When this vesicle fuses with the plasma membrane, the entire Krt1 protein will be
secreted into the extracellular space. (b)
When this vesicle fuses with the plasma membrane, the C-terminus of Krt1 will be
inserted into the plasma membrane. (c)
When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space. (d)
When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be cytoplasmic.
15-58 For each of the following sentences, choose one of the two options enclosed in square
brackets to make a correct statement.
New plasma membrane reaches the plasma membrane by the [regulated/constitutive]
exocytosis pathway. New plasma membrane proteins reach the plasma membrane by the
[regulated/constitutive] exocytosis pathway. Insulin is secreted from pancreatic cells by
the [regulated/constitutive] exocytosis pathway. The interior of the trans Golgi network
is [acidic/alkaline]. Proteins that are constitutively secreted [aggregate/do not aggregate]
in the trans Golgi network.
15-59 In a cell capable of regulated secretion, what are the three main classes of proteins that
must be separated before they leave the trans Golgi network? Endocytic Pathways lOMoAR cPSD| 59078336
15-60 For each of the following sentences, fill in the blanks with the best word or phrase selected
from the list below. Not all words or phrases will be used; each word or phrase should be used only once.
Eukaryotic cells are continually taking up materials from the extracellular space by the
process of endocytosis. One type of endocytosis is __________________, which uses
__________________ proteins to form small vesicles containing fluids and molecules.
After these vesicles have pinched off from the plasma membrane, they will fuse with the
__________________, where materials that are taken into the vesicle are sorted. A second
type of endocytosis is __________________, which is used to take up large vesicles that
can contain microorganisms and cellular debris. Macrophages are especially suited for this
process, as they extend __________________ (sheetlike projections of their plasma
membrane) to surround the invading microorganisms. chaperone Golgi apparatus pseudopods cholesterol mycobacterium rough ER clathrin phagocytosis SNARE endosome pinocytosis transcytosis
15-61 Which of the following statements about phagocytic cells in animals is false? (a)
Phagocytic cells are important in the gut to take up large particles of food. (b)
Phagocytic cells scavenge dead and damaged cells and cell debris. (c)
Phagocytic cells can engulf invading microorganisms and deliver them to their lysosomes for destruction. (d)
Phagocytic cells extend pseudopods that surround the material to be ingested.
15-62 Name three possible fates for an endocytosed molecule that has reached the endosome.
15-63 If a lysosome breaks, what protects the rest of the cell from lysosomal enzymes?
15-64 You are working in a biotech company that has discovered a small-molecule drug called
H5434. H5434 binds to LDL receptors when they are bound to cholesterol. H5434 binding
does not alter the conformation of the LDL receptor’s intracellular domain. Interestingly,
in vitro experiments demonstrate that addition of H5434 increases the affinity of LDL for
cholesterol and prevents cholesterol from dissociating from the LDL receptor even in acidic
conditions. Which of the following is a reasonable prediction of what may happen when
you add H5434 to cells? (a)
Cytosolic cholesterol levels will remain unchanged relative to normal cells. (b)
Cytosolic cholesterol levels will decrease relative to normal cells. (c)
The LDL receptor will remain on the plasma membrane. (d) The uncoating of vesicles will not occur. lOMoAR cPSD| 59078336
15-65 Fibroblast cells from patients W, X, Y, and Z, each of whom has a different inherited defect,
all contain “inclusion bodies,” which are lysosomes filled with undigested material. You
wish to identify the cellular basis of these defects. The possibilities are: 1.
a defect in one of the lysosomal hydrolases 2.
a defect in the phosphotransferase that is required for mannose-6-phosphate tagging of the lysosomal hydrolases 3.
a defect in the mannose-6-phosphate receptor, which binds mannose-6-
phosphatetagged lysosomal proteins in the trans Golgi network and delivers them to lysosomes
When you incubate some of these mutant fibroblasts in a medium in which normal cells
have been grown, you find that the inclusion bodies disappear. Because of these results,
you suspect that the constitutive exocytic pathway in normal cells is secreting lysosomal
hydrolases that are being taken up by the mutant cells. (It is known that some mannose-
6phosphate receptor molecules are found in the plasma membrane and can take up and
deliver lysosomal proteins via the endocytic pathway.) You incubate cells from each patient
with medium from normal cells and medium from each of the other mutant cell cultures,
and get the results summarized in Table Q15-65. Table Q15-65
Indicate which defect (1, 2, 3) each patient (W, X, Y, Z) is most likely to have.
How We Know: Tracking Protein and Vesicle Transport
15-66 You have created a green fluorescent protein (GFP) fusion to a protein that is normally
secreted from yeast cells. Because you have learned about the use of temperaturesensitive
mutations in yeast to study protein and vesicle transport, you obtain three mutant yeast
strains, each defective in some aspect of the protein secretory process. Being a good
scientist, you of course also obtain a wild-type control strain. You decide to examine the
fate of your GFP fusion protein in these various yeast strains and engineer the mutant strains
to express your GFP fusion protein. However, in your excitement to do the experiment, you lOMoAR cPSD| 59078336
realize that you did not label any of the mutant yeast strains and no longer know which
strain is defective in what process. You end up numbering your strains with the numbers 1
to 4, and then you carry out the experiment anyway, obtaining the results shown in Figure
Q15-66 (the black dots represent your GFP fusion protein). Figure Q15-66
Name the process that is defective in each of these strains. Remember that one of these
strains is your wild-type control.