Ch. 8
Why is the ER so well-suited and ideally constructed for its role as a port of entry for secretory proteins? 1) It has a large surface area allowing the attachment of many ribosomes. 2) The ER cisternae lumen favors unfolding and disassembly of proteins. 3) The RER can segregate secretory, lysosomal and cytoplasmic proteins from other newly made proteins, allowing their modification, and sends them to their final destination. a) 1 b) 2 c) 3 d) 1 and 3 e) 1, 2, and 3
a) 1
Why does the cell use proteasomes to destroy misfolded proteins? a) Destruction of misfolded proteins assures that aberrant proteins are not sent to other parts of the cell. b) These proteins can be degraded into components that can be used to make polynucleotides. c) These proteins are degraded into components that can be used to make polysaccharides. d) These proteins are degraded into components that are used to make lipids. e) Destruction of misfolded proteins prevents the dissolution of the plasma membrane.
a) Destruction of misfolded proteins assures that aberrant proteins are not sent to other parts of the cell.
What happens to the clathrin coat once the vesicle has budded from the Golgi body? a) It is lost. b) It is strengthened. c) It is rearranged. d) It is thickened. e) It swells.
a) It is lost
What is usually the retrieval signal for ER integral membrane proteins, like the SRP receptor? a) KKXX at the C-terminus of the protein b) KDEL at the C-terminus of the protein c) KDEL at the N-terminus of the protein d) KKXX at the N-terminus of the protein e) KXEL at the C-terminus of the protein
a) KKXX at the C-terminus of the protein
What is the effect of CDG1b on cell physiology and what is the treatment that has shown some promise of being effective? a) Mannose is unavailable for incorporation into oligosaccharides; oral supplements of mannose are the treatment. b) Mannose is available for incorporation into oligosaccharides; oral supplements of mannose are the treatment. c) Mannose is unavailable for incorporation into oligosaccharides; a diet free of mannose is the treatment. d) Mannose is available for incorporation into oligosaccharides; a diet free of mannose is the treatment. e) Fructose is unavailable for incorporation into oligosaccharides; oral supplements of fructose are the treatment.
a) Mannose is unavailable for incorporation into oligosaccharides; oral supplements of mannose are the treatment.
Cells are infected with a vesicular stomatitis virus (VSV) strain in which a viral gene (VSVG) is fused to the green fluorescent protein gene. When the chimeric protein is synthesized, what pathway does it follow from synthesis until it leaves the cell? a) RER, Golgi complex, plasma membrane, viral envelopes b) RER, Golgi complex, viral envelopes, plasma membrane c) Golgi complex, RER, plasma membrane, viral envelopes d) RER, Golgi complex, mitochondria, plasma membrane, viral envelopes e) RER, mitochondria, Golgi complex, plasma membrane, viral envelopes
a) RER, Golgi complex, plasma membrane, viral envelopes
What GTP-binding protein plays a regulatory role by initiating vesicle formation and by regulating the assembly of the vesicle's COPII coat? a) Sar1 b) Gar1 c) ARF1 (adenosylation ribose factor) d) Ras e) Src
a) Sar1
What evidence suggests that the translocon, by itself, can properly orient transmembrane segments? a) Studies performed with purified components in cell-free systems show that the translocon, by itself, is capable of properly orienting transmembrane segments. b) Reconstituted translocons properly oriented membrane proteins in a natural membrane. c) Translocons orient proteins in red blood cells when exposed to them. d) Translocons bind to proteins in vitro. e) When translocons are missing, membrane proteins are not appropriately oriented.
a) Studies performed with purified components in cell-free systems show that the translocon, by itself, is capable of properly orienting transmembrane segments.
What kind(s) of modifications are made in proteins as they move through the Golgi complex? a) The protein's carbohydrates are modified by a series of stepwise enzymatic reactions. b) Amino acids can be added to either end of the polypeptide chain. c) Amino acids in the proteins may be chemically altered into nucleic acids. d) Small segments of amino acids can be added into the center of an existing protein. e) All of these are correct.
a) The protein's carbohydrates are modified by a series of stepwise enzymatic reactions.
What appears to be the purpose of molecular chaperones like BiP? a) They recognize and bind to unfolded or misfolded proteins and help them attain their native structure. b) They recognize and bind to unfolded or misfolded DNAs and help them attain their native structure. c) They recognize and bind to unfolded or misfolded RNAs and help them attain their native structure. d) They recognize and bind unfolded or misfolded carbohydrates and help them lose their native shape. e) They transport secretory proteins into secretory vesicles.
a) They recognize and bind to unfolded or misfolded proteins and help them attain their native structure.
What allows the interface between the Sec13-Sec31 subunits to form cages of varying diameter, thus accommodating vesicles of varying size? a) a degree of flexibility built into the interface between the Sec13-Sec31 subunits b) a degree of rigidity built into the interface between the Sec13-Sec31 subunits c) a degree of extensibility built into the interface between the Sec13-Sec31 subunits d) a protein between Sec13 and Sec31 that allows free rotation e) Sec24, which provides a cushion between the Sec13 and Sec31 subunits
a) a degree of flexibility built into the interface between the Sec13-Sec31 subunits
A control cell that is synthesizing a GFP-labeled version of mannosidase II has fluorescence localized in the numerous Golgi complexes of the cell. Normally, this enzyme is synthesized in the endoplasmic reticulum and moves via transport vesicles to the Golgi complex, where it takes up residence. If an experimental cell contains an siRNA that leads to the fluorescence being restricted to the endoplasmic reticulum, with what would the siRNA be likely to interfere? a) an mRNA that codes for a protein involved in the transport of the enzyme from the ER to the Golgi complex b) an rRNA that synthesizes the enzyme c) the synthesis of mannosidase II from its mRNA d) an mRNA that codes for a protein involved in the transport of the enzyme from the Golgi complex to the ER e) an mRNA that codes for the enzyme
a) an mRNA that codes for a protein involved in the transport of the enzyme from the ER to the Golgi complex
Lysosomal enzymes are transported from the TGN in vesicles coated with what protein? a) clathrin b) lysozyme c) dynamin d) acid phosphatase e) COPII
a) clathrin
What is responsible for adding sugars to dolichol phosphate? a) membrane-bound glycosyltransferases b) membrane-bound oligosaccharyltransferase c) membrane-bound gangliosidase d) glycosylsynthetase e) peptidyltransferase
a) membrane-bound glycosyltransferases
What is the arrangement of organelles in a secretory cell from the basal end to the apical end, an arrangement that reflects the flow of secretory products from synthesis to discharge? a) nucleus and RER - SER - Golgi complex - secretory vesicles b) Golgi complex - nucleus and RER - SER - secretory vesicles c) nucleus and RER - Golgi complex - SER - secretory vesicles d) SER - nucleus and RER - Golgi complex - secretory vesicles e) secretory vesicles - nucleus and RER - SER - Golgi complex
a) nucleus and RER - SER - Golgi complex - secretory vesicles
Which of the proteins below is(are) not made on the membrane-bound ribosomes of the RER? a) peripheral proteins of the inner surface of the plasma membrane b) soluble lysosomal proteins c) vacuolar enzymes d) proteins of the extracellular matrix e) All of these are correct.
a) peripheral proteins of the inner surface of the plasma membrane
TB 8.008 Elevated temperatures at which temperature-sensitive mutants do not work are called ________ temperatures. a) restrictive b) permissive c) temperature-sensitive d) frame-shift e) point
a) restrictive
Which type of cells below is not known for its extensively developed SER? a) skin cells b) kidney tubule cells c) skeletal muscle cells d) steroid-producing endocrine cells e) both skeletal muscle cells and kidney tubule cells
a) skin cells
Which of the models below suggests that the Golgi cisternae are transient structures that form at the cis face of the stack by fusion of membranous carriers from the ER and ERGIC and that each cisterna travels through the Golgi complex from the cis to the trans end of the stack, changing in composition as it progresses? a) the cisternal maturation model b) the cargo carrying model c) the vesicular transport model d) the secretory transport model e) the chemiosmotic model
a) the cisternal maturation model
The accumulation of misfolded proteins in the ER is a potentially lethal situation and thus causes the triggering of what process? a) the unfolded protein response (UPR) b) the posttranscriptional response c) the polysomal response d) the proteasomal response e) the intracellular protein response
a) the unfolded protein response (UPR)
Sec23 and Sec24 bind together to form a "banana-shaped" dimer. What is the purpose of this dimer a) Because of its linear shape, it firms up the membrane. b) Because of its curved shape, the dimer puts pressure on the membrane surface to help it further bend into a curved bud. c) Because of its curved shape, the dimer puts pressure on the membrane surface to help it disintegrate. d) The dimer stabilizes the Golgi complex membrane. e) The dimer joins with other dimers to form a remarkably stable cage.
b) Because of its curved shape, the dimer puts pressure on the membrane surface to help it further bend into a curved bud.
Which coated vesicles move materials in a retrograde direction from the ERGIC and Golgi stack backwards toward the ER? a) COPII-coated vesicles b) COPI-coated vesicles c) clathrin-coated vesicles d) cadmium-coated vesicles e) both COPII-coated vesicles and COPI-coated vesicles
b) COPI-coated vesicles
How is the orientation of membrane proteins in the membrane thought to be accomplished? a) After synthesis, an enzyme orients the protein properly. b) During synthesis, the translocon inner lining orients the nascent polypeptide so the more positive end faces the cytosol. c) During synthesis, the translocon inner lining orients the nascent polypeptide so the more negative end faces the cytosol. d) During synthesis, the translocon inner lining orients the nascent polypeptide so the more positive end faces the mitochondrial intermembrane space. e) After synthesis, the translocon inner lining orients the nascent polypeptide so the more positive end faces the cytosol.
b) During synthesis, the translocon inner lining orients the nascent polypeptide so the more positive end faces the cytosol.
What mediates the interaction between integral membrane proteins to be transported in COPII-coated vesicles and the COPII-coat? a) ER export signals in the luminal tails of integral ER membrane proteins b) ER export signals in the cytosolic tails of integral ER membrane proteins c) ER export signals in ER phospholipids that interact with the membrane proteins d) ER export signals in carbohydrates on the cytosolic tails of integral ER membrane proteins e) ER export signals in carbohydrates on the luminal tails of integral ER membrane proteins
b) ER export signals in the cytosolic tails of integral ER membrane proteins
How and where is the asymmetry of the phospholipid bilayers initially established? a) It is initially established in the Golgi complex during lipid and protein modification. b) It is initially established in the ER during lipid and protein synthesis. c) It is initially established in the secretory vesicles during lipid and protein modification d) It is initially established in the mitochondria by random insertion into the membranes. e) All of these are correct.
b) It is initially established in the ER during lipid and protein synthesis.
What are the recognition signals for lysosomal enzymes that allow them to be localized correctly in lysosomes? a) Lysosomal enzymes possess sulfated mannose residues on N-linked carbohydrate chains. b) Lysosomal enzymes possess phosphorylated mannose residues on N-linked carbohydrate chains. c) Lysosomal enzymes possess phosphorylated mannose residues on O-linked carbohydrate chains. d) Lysosomal enzymes possess sulfated mannose residues on O-linked carbohydrate chains. e) Lysosomal enzymes possess phosphorylated glucose residues on N-linked carbohydrate chains.
b) Lysosomal enzymes possess phosphorylated mannose residues on N-linked carbohydrate chains.
What effect does the binding of the SRP to the growing polypeptide chain and the ribosome have on protein synthesis? a) Protein synthesis accelerates. b) Protein synthesis ceases temporarily. c) Protein synthesis ceases permanently. d) Protein synthesis is terminated. e) The ribosome dissociates.
b) Protein synthesis ceases temporarily.
How are integral membrane proteins thought to enter the lipid bilayer? a) They insert into the membrane from the RER lumen after their synthesis is complete. b) The aqueous translocon channel seems to have a gate that continuously opens and closes, giving each nascent polypeptide segment a chance to partition itself into the lipid bilayer's hydrophobic core. c) They insert into the membrane from the cytosol after their synthesis is complete. d) It is thought that they burrow into the lipid bilayer. e) It is thought that they are enzymatically implanted in the lipid bilayer.
b) The aqueous translocon channel seems to have a gate that continuously opens and closes, giving each nascent polypeptide segment a chance to partition itself into the lipid bilayer's hydrophobic core.
How do protein coats select the cargo molecules to be carried by the vesicles they help to form? a) They electromagnetically attract the correct cargo proteins. b) The protein coats have a specific affinity for the cytosolic tails of integral membrane proteins that reside in the donor membrane. c) The coats have a specific affinity for the luminal tails of integral membrane proteins that reside in the donor membrane. d) The coat proteins directly attach to the cargo proteins in the lumen of the forming vesicles. e) The coat proteins attach to the extracellular matrix.
b) The protein coats have a specific affinity for the cytosolic tails of integral membrane proteins that reside in the donor membrane.
TB 8.014 You incubate liposomes with a series of purified proteins normally found in the coats of cell transport vesicles. After adding one of them to the liposome mixture, budding of vesicles from the liposomes began. What does this mean? a) Liposomes cause the protein to denature. b) The protein is involved in the initiation of vesicle formation. c) The protein is involved in liposome denaturation. d) The protein triggers protein synthesis. e) The protein causes the entry of water into the liposomes.
b) The protein is involved in the initiation of vesicle formation
Phospholipids are made by integral ER membrane enzymes whose active sites face the cytosol and they are inserted into the outer (cytoplasmic) leaflet of the ER membrane. How then do lipids destined for the luminal leaflet of the ER membrane get there? a) They diffuse freely into the luminal leaflet. b) There are enzymes called flippases that flip these lipids later into the opposite leaflet. c) They are disassembled on the cytoplasmic side and reassembled on the luminal side. d) They move to the cytoplasmic leaflet by osmosis. e) There are enzymes called translocases that flip these lipids later into the opposite leaflet.
b) There are enzymes called flippases that flip these lipids later into the opposite leaflet.
What happened to COPI-coated vesicles within the cell when the cell was treated with GTP analogues that could not be hydrolyzed? a) They accumulated in the nucleus. b) They accumulated in the cytoplasm. c) They fused into one giant vesicle that was seen in the cytoplasm. d) They decreased substantially in number in the nucleus. e) They decreased substantially in number in the cytoplasm.
b) They accumulated in the cytoplasm.
Cells are infected with a virus carrying a temperature-sensitive mutant VSVG gene that encodes a protein that cannot leave the ER of infected cells grown at restrictive temperatures. Thus, at higher temperatures, ______________. a) VSVG protein heads immediately for the Golgi complex. b) VSVG protein cannot leave the ER. c) VSVG protein leaves the ER immediately. d) All of the manufactured VSVG protein leaves the ER synchronously. e) VSVG protein is degraded rapidly and never passes to the Golgi complex.
b) VSVG protein cannot leave the ER.
What do studies suggest governs the "decision" to destroy a defective protein that has been unable to fold correctly and has been in the ER for an extended period of time? a) a fast-acting ER enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein b) a slow-acting ER enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein c) a fast-acting cytoplasmic enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein d) a slow-acting nuclear enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein e) a slow-acting cytoplasmic enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein
b) a slow-acting ER enzyme that trims a mannose residue from an exposed end of the oligosaccharide of a protein
What is the general name for a molecule that physically links two different types of materials? a) enzymes b) adaptors c) structural proteins d) receptors e) polynucleotides
b) adaptors
To what residue of a polypeptide are N-linked oligosaccharide chains attached as that poypeptide enters the RER lumen through the translocon? a) arginine b) asparagine c) serine d) threonine e) ninhydrin
b) asparagine
Enzymes can be purified from the microsomal fraction. They can then be used as antigens to make antibodies. The antibodies can then be exposed to cells and later visualized in the electron microscope. What allows them to be seen in the electron microscope? a) attachment of amino acids to the antibody b) attachment of gold particles to the antibodies c) attachment of nonradioactive amino acids to the antibodies d) degradation of the antibodies e) shrinkage of the antibodies
b) attachment of gold particles to the antibodies
The SRP and SRP receptor are thought to bind GTP ______ interacting with each other. a) while b) before c) after d) before and after e) instead of
b) before
Studies of cell physiology that occur in test tubes that do not contain whole cells are called ______. a) in vivo systems b) cell-free systems c) test tube systems d) onsite systems e) cellonic systems
b) cell-free systems
What are the two sites within a cell at which protein synthesis is generally thought to occur? a) cytosolic surface of RER and cisternal surface of RER b) cytosolic surface of RER and free ribosomes c) cisternal surface of RER and free ribosomes d) free ribosomes and cytosolic surface of SER e) cytosolic surface of RER and cytosolic surface of SER
b) cytosolic surface of RER and free ribosomes
Most vesicles budding from the Golgi body have a fuzzy, electron-dense coat on their ______ surface. The coat appears to be made of _______. a) luminal, protein b) cytosolic, protein c) luminal, lipid d) cytosolic, carbohydrate e) cytosolic, lipid
b) cytosolic, protein
What is the name sometimes given to a single Golgi stack in a plant cell? a) endosome b) dictyosome c) flagosome d) ribosome e) plantosome
b) dictyosome
The endomembrane system when homogenized is broken up into vesicles, which are heterogeneous but similar in size. These vesicles can be purified and, after purification, often retain their biological activity. They are collectively referred to as _________. a) endosomes b) microsomes c) ribosomes d) minisomes e) lysosomes
b) microsomes
What is the name for a brief incubation of a tissue with radioactivity during which labeled amino acids are incorporated into protein? a) chase b) pulse c) pulse-chase d) labelard e) statin
b) pulse
Which part of the Golgi complex is thought to function primarily as a sorting station that distinguishes between proteins to be shipped back to the ER and those that are allowed to proceed to the next Golgi station? a) the cis cisternae b) the CGN c) the medial cisternae d) the trans cisternae e) the trans-Golgi network
b) the CGN
Where in the Golgi complex does most protein sorting occur? a) the medial cisternae b) the TGN c) the CGN d) the cis network e) the pre-Golgi network
b) the TGN
With what structure is the RER often seen to be continuous, as seen by its association with ribosomes? a) the inner membrane of the nuclear envelope b) the outer membrane of the nuclear envelope c) the outer mitochondrial membrane d) the outer chloroplast membrane e) the Golgi complex
b) the outer membrane of the nuclear envelope
What determines the sequence of sugar addition to glycoproteins traveling through the Golgi complex? a) Nothing - the sequence is random. b) the spatial arrangement of specific glycosyltransferases that contact proteins as they pass through the Golgi complex c) the concentration of sugars in the Golgi complex d) the concentration of sugars in the Golgi complex e) the sequence of nucleotides in the Golgi complex
b) the spatial arrangement of specific glycosyltransferases that contact proteins as they pass through the Golgi complex
What accounts for the differences in function between the types of ER? 1) the location of the ER 2) the proximity of the ER to the nucleus 3) the protein content of the ER 4) the shape of its component lipids a) 1 b) 2 c) 3 d) 4 e) 1 and 2
c) 3
What GTP-binding protein is associated with the formation of the COPI coat on COPI-coated vesicles? a) Sar1 b) Arf Arf c) ARF1 (adenosylation ribose factor) d) Ras e) Src
c) ARF1 (adenosylation ribose factor)
Which GTP-binding protein is associated with clathrin-coated vesicles and helps to initiate the formation of the coat? a) Sar1 b) Raf Raf1 c) ARF1 (adenosylation ribose factor) d) Ras e) Src
c) ARF1 (adenosylation ribose factor)
What does the conformation-sensing enzyme GT do if it binds to a misfolded or incompletely folded glycoprotein? a) It degrades the oligosaccharide chain. b) It adds a single mannose back to one of the glucose residues at the exposed end of the recently trimmed oligosaccharide. c) It adds a single glucose back to one of the mannose residues at the exposed end of the recently trimmed oligosaccharide. d) It degrades the protein. e) It refolds the protein on its own.
c) It adds a single glucose back to one of the mannose residues at the exposed end of the recently trimmed oligosaccharide.
What would happen if the enzyme that adds phosphate groups to the appropriate mannose residues on the carbohydrate chains of lysosomal enzymes were defective? a) Lysosomal enzymes would be localized to lysosomes. b) Lysosomal enzymes would be localized to peroxisomes. c) Lysosomal enzymes would continue through the Golgi complex to secretory vesicles and would eventually be secreted. d) Lysosomal enzymes would be degraded. e) Lysosomal enzymes would be degraded.
c) Lysosomal enzymes would continue through the Golgi complex to secretory vesicles and would eventually be secreted.
A cellular phenomenon called _________ is a process in which cells produce small RNAs that bind to specific mRNAs and inhibit the translation of these mRNAs into proteins. a) RNAi b) cRNAs c) RNAi and RNA interference d) RNA interference e) RNAa
c) RNAi and RNA interference
What is the primary adaptor protein of the COPII coat that interacts specifically with the ER export signals in the cytosolic tails of membrane proteins that are destined to traffic on to the Golgi complex? a) ARF1 b) Sec23 c) Sec24 d) Sec31 e) Sec13
c) Sec24
How does GT recognize incompletely folded or misfolded proteins that have been recently synthesized? a) Such proteins display exposed hydrophilic residues that are absent from properly folded proteins. b) Five histidine residues are exposed on the protein's surface when it is improperly folded. c) Such proteins display exposed hydrophobic residues that are absent from properly folded proteins. d) Six arginine residues are exposed on the protein's surface when it is improperly folded. e) Such proteins display numerous carboxyl groups on their surfaces, which decreases their solubility.
c) Such proteins display exposed hydrophobic residues that are absent from properly folded proteins.
What happens if the UPR is unsuccessful in relieving the stressful conditions in the cell? a) The cell grows. b) The cell divides. c) The cell-death pathway is triggered and the cell is destroyed. d) The cell shrinks. e) The cell's temperature is raised.
c) The cell-death pathway is triggered and the cell is destroyed.
What are the differences between ribosomes that make secretory proteins and those that make proteins intended for the cytosol? a) The ribosomes that make secretory proteins are smaller. b) The ribosomes that make cytosolic proteins are larger. c) There are no differences between them. d) The ribosomes that make secretory proteins are denser. e) The ribosomes that secretory proteins have extra subunits.
c) There are no differences between them.
What is one problem created by the detoxifying enzymes of the SER? a) They often create compounds that cause excessive weight gain. b) They often create compounds that cause excessive weight loss. c) They can cause a compound to be converted into a carcinogen. d) They can cause the denaturation of an essential enzyme or protein. e) They can lead to addiction
c) They can cause a compound to be converted into a carcinogen.
What happens to yeast cells that cannot transport proteins into the ER lumen cotranslationally? a) The die. b) They hibernate. c) They survive, but grow more slowly than normal yeast cells. d) They divide more frequently. e) Their lifespans are lengthened
c) They survive, but grow more slowly than normal yeast cells.
What always serves as the donor of a sugar to the growing oligosaccharide chain of a glycoprotein? a) a sugared nucleotide b) a nucleotide peptide c) a nucleotide sugar d) a sugar e) ATP
c) a nucleotide sugar
In a pulse-chase procedure, if the chase is longer, which statement below correctly describes the location of the radioactively labeled proteins in the cell? a) closer to the synthesis site b) farther from the nucleus c) farther from the synthesis site d) closer to the nucleus e) farther from the mitonchondria
c) farther from the synthesis site
Which procedure below would lead to the visualization of the dynamic movements of specific proteins as they move through a single living cell? The proteins can be seen through the microscope eyepiece and the cells do not have to be killed for the protein to be detected. a) pulse-chase b) fusion of the green fluorescent protein gene to the protein that is to be tracked through the cell c) fusion of the green fluorescent protein gene to the gene encoding the protein to be tracked through the cell d) pulse-chase using fluorescent antibodies e) all of these are correct
c) fusion of the green fluorescent protein gene to the gene encoding the protein to be tracked through the cell
What enzymes are responsible for determining the sequence of sugars added to growing oligosaccharide chains of membrane proteins or secretory proteins as they travel through the Golgi complex? a) glycosaminocosidases b) peptidyltransferases c) glycosyltransferase d) amylases e) Rubisco
c) glycosyltransferase
What sugar is usually removed from the N-linked core oligosaccharide chains on proteins in the Golgi complex as opposed to the glucose residues trimmed off in the ER? a) glucose b) galactose c) mannose d) sialic acid e) fucose
c) mannose
The movement of vesicular-tubular carriers (VTCs) farther away from the ER and toward the Golgi complex occurs along tracks composed of what material? a) RNA b) DNA c) microtubules d) microfilaments e) intermediate filaments
c) microtubules
The ER reportedly contains sensors that monitor the concentration of unfolded or misfolded proteins in the lumen. One proposal suggests that the sensors are normally kept in an inactive state by ______, particularly ______. a) molecular chaperones, ribosomes b) proteasomes, BiP c) molecular chaperones, BiP d) enzymes, ER e) molecular chaperones, Rubisco
c) molecular chaperones, BiP
What enzyme transfers a block of sugars to asparagine residues of a polypeptide as it enters the RER? a) glycosyltransferase b) acid phosphatase c) oligosaccharyltransferase d) cellulose e) glycolase
c) oligosaccharyltransferase
CDG1b results from a deficiency in what enzyme? a) phosphomannose phosphatase b) phosphotungstate isomerase c) phosphomannose isomerase d) phosphatase e) phosphoenol pyruvate carboxylase
c) phosphomannose isomerase
A tissue has been briefly labeled with radiolabeled amino acids. It is then transferred to a medium containing unlabeled amino acids. This can be done several times with different tissue samples for varying periods of time. What is the entire procedure called? a) chase b) pulse c) pulse-chase d) labelard e) statin
c) pulse-chase
Vesicles that move through the Golgi complex from a trans-donor to a cis-acceptor membrane are said to move in a(n) __________ direction. a) astrograde b) anterograde c) retrograde d) awful grade e) verigrade
c) retrograde
To what site does Sar1 bind after it binds to GTP? a) the luminal leaflet of the ER membrane b) the luminal leaflet of the ER membrane c) the cytosolic leaflet of the ER bilayer d) the luminal leaflet of the Golgi membrane e) the cytosolic leaflet of the plasma membrane
c) the cytosolic leaflet of the ER bilayer
Which model of Golgi complex formation suggests that the cisternae of a Golgi stack remain in place as stable compartments held together by a protein scaffold, while the cargo is shuttled through the Golgi via vesicles that bud from one compartment and fuse with a neighboring one? a) the cisternal maturation model b) the cargo carrying model c) the vesicular transport model d) the secretory transport model e) the chemiosmotic model
c) the vesicular transport model
The oligosaccharide block that is added to secretory proteins after they enter the ER lumen goes through a number of modifications after its attachment. What is the first modification that occurs? a) addition of more sugars b) addition of glucose c) trimming of some sugars from the oligosaccharide block d) chemical modification of the sugars on the oligosaccharide chain e) both addition of more sugars and addition of glucose
c) trimming of some sugars from the oligosaccharide block
When cells are homogenized, the cytomembrane system is broken into fragments, the ends of which can fuse to form small membranous spheres called ________. a) vacuoles b) victuals c) vesicles d) nuclei e) endosomes
c) vesicles
Why is RNAi now used as a strategy for investigating the effect of a missing protein more often than generating an organism that possesses a mutant gene? a) It is easier to generate an organism that possesses a mutant gene than to synthesize a small RNA. b) Small RNAs are less stable than organisms. c) Mutant genes are much easier to synthesize. d) It is easier to synthesize a small RNA than to generate an organism that possesses a mutant gene. e) Small RNAs are much more sensitive.
d) It is easier to synthesize a small RNA than to generate an organism that possesses a mutant gene
What happens if misfolded proteins are generated in the ER at a faster rate than they can be exported to the cytoplasm? a) They are degraded in the ER. b) They are inserted into the ER membrane. c) They are resynthesized in the ER. d) They accumulate in the ER. e) They accumulate in the Golgi complex.
d) They accumulate in the ER.
What happens to a newly synthesized glycoprotein after the binding of calnexin or calreticulin to help the protein correctly complete its folding? a) When the glycoprotein's folding is correctly completed, the remaining glucose on its oligosaccharide chain is eventually reduced and the glycoprotein is released from the chaperone. b) The oligosaccharide chain is totally degraded. c) Nothing happens. d) When the glycoprotein's folding is correctly completed, the remaining glucose on its oligosaccharide chain is eventually removed enzymatically and the glycoprotein is released from the chaperone. e) The oligosaccharide chain is totally degraded.
d) When the glycoprotein's folding is correctly completed, the remaining glucose on its oligosaccharide chain is eventually removed enzymatically and the glycoprotein is released from the chaperone.
Where are misfolded secretory proteins eventually destroyed? a) in the RER b) in the SER c) in the Golgi complex d) in the cytosol (cytoplasm) e) in the nucleus
d) in the cytosol (cytoplasm)
What determines the function of a cell's smooth endoplasmic reticulum? a) its lipid content b) its polynucleotide content c) its carbohydrate content d) its protein content e) its age
d) its protein content
What is responsible for degrading misfolded proteins in the cytoplasm? a) polysomes b) polyribosomes c) peroxisomes d) proteasomes e) spliceosome
d) proteasomes
The separation of organelles or vesicles derived from different organelles is called ______. a) cell division b) mitosis c) meiosis d) subcellular fractionation e) cell ostentation
d) subcellular fractionation
TB 8.034 Blöbel, Sabatini and Dobberstein proposed that the site of protein synthesis is determined by information contained in the N-terminal portion of the protein, the first part to emerge from the ribosome. What did they call their proposal? a) the Chemiosmotic Hypothesis b) the Posttranslational Hypothesis c) the SRP Hypothesis d) the Signal Hypothesis e) the Cotranslational Hypothesis
d) the Signal Hypothesis
What allows smooth and rough vesicles (microsomes) to be readily separated by density gradient centrifugation? a) their size differences b) their differences in lipid composition c) their differences in color d) their differences in density e) their differences in water content
d) their differences in density
What is the fate of a misfolded or incompletely folded protein in the ER once one or more of its mannose residues has been removed from its oligosaccharide chain(s)? 1) The protein can no longer be recycled. 2) The protein is recycled. 3) The protein is sentenced to degradation. 4) The protein continues to be refolded. a) 1 b) 2 c) 3 d) 4 e) 1 and 3
e) 1 and 3
A control cell that is synthesizing a GFP-labeled version of mannosidase II has fluorescence localized in the numerous Golgi complexes of the cell. Normally, this enzyme is synthesized in the endoplasmic reticulum and moves via transport vesicles to the Golgi complex, where it takes up residence. What would an experimental cell look like if it contained an siRNA that led to the absence of one of the proteins involved in the transport of the enzyme from the ER to the Golgi complex? 1) Fluorescent label is not found in the Golgi complex. 2) The GFP-mannosidase II is denatured so there is no fluorescent label anywhere in the cell. 3) Fluorescent label still translocates the Golgi complex completely. 4) Fluorescent label is found only in the endoplasmic reticulum. a) 1 b) 2 c) 3 d) 3 and 4 e) 1 and 4
e) 1 and 4
Which of the following are enzymes that are involved in detoxification of organic compounds in the SER of liver cells? 1) oxygen-transferring enzymes 2) oxygenases 3) members of the cytochrome P450 family 4) oxidases a) 1 b) 2 c) 3 d) 4 e) 1, 2 and 3
e) 1, 2 and 3
What is responsible for recognizing lysosomal enzymes and localizing them to the lysosomes? 1) mannose 6-phosphate receptors 2) MPRs 3) integral membrane proteins that span the TGN membranes 4) intraGolgi receptors that reside in the TGN lumen a) 1 b) 1, 2, and 4 c) 3 d) 4 e) 1, 2, and 3
e) 1, 2, and 3
Which of the following is a function associated with the smooth endoplasmic reticulum in at least some cells? a) synthesis of steroid hormones b) detoxification of many organic compounds, like barbiturates and ethanol c) release of glucose into the bloodstream d) sequestration of calcium Ca2+ ions within the cisternal space e) All of these are correct
e) All of these are correct
The coat of vesicles that transport materials around the cell interior ___________. a) is composed of two distinct protein layers b) possesses an outer cage or scaffolding that forms the framework for the coat c) possesses adaptors that are able to select specific cargo molecules d) possesses an inner layer of adaptors that serves primarily to bind the vesicle's cargo e) All of these are correct.
e) All of these are correct.
When electron micrographs were first taken of the cell interior, what kinds of membranous structures were seen? a) membrane-bound vesicles of varying diameter, containing material of different electron density b) long channels bounded by membranes and radiating through the cytoplasm c) an interconnected network of canals d) stacks of flattened, membrane-bound sacs called cisternae e) All of these are correct.
e) All of these are correct.
Why are yeast cells often used to study eukaryotic gene mutations affecting secretion and other cytomembrane processes? a) They have only a few genes. b) They are small and single-celled and can be cultured easily. c) They can be grown as haploid organisms so mutants are easily seen. d) Deficiencies in yeast cells caused by mutants are easily detected. e) All of these are correct.
e) All of these are correct.
What components below are selected for transport by vesicles originating in the Golgi complex? a) secretory proteins b) lysosomal proteins c) proteins required to dock the vesicle to an acceptor membrane d) proteins required to target the vesicle to an acceptor membrane e) All of these components.
e) All of these components.
What is the effect on a yeast cell of the presence of a mutant gene involved in vesicle fusion? a) The ER shrank. b) The nucleus became swollen. c) The Golgi complex expanded greatly. d) Cells accumulated expanded ER cisternae. e) Cells amassed an excess number of unfused vesicles.
e) Cells amassed an excess number of unfused vesicles.
How do misfolded proteins get to the cytoplasm to be destroyed? a) They diffuse freely through the lipid bilayer. b) A process called reverse transcription takes proteins back through the translocons they passed through on their way into the ER lumen. c) They diffuse through gap junctions. d) An enzyme flips them through the hydrophobic part of the lipid bilayer. e) Proteins are transported back to the cytosol through the translocon that brought them into the ER lumen or through a separate dislocation channel of uncertain identity.
e) Proteins are transported back to the cytosol through the translocon that brought them into the ER lumen or through a separate dislocation channel of uncertain identity.
Which protein(s) below is(are) recruited to the COPII coat by Sar1-GTP? a) ARF1 b) Sec23 c) Sec32 d) Sec24 e) both Sec23 and Sec24
e) both Sec23 and Sec24
What subunit(s) of the COPII coat bind(s) to the vesicle membrane to form the outer structural cage of the protein coat? a) Sec31 b) Sec24 c) Sec23 d) Sec13 e) both Sec31and Sec13
e) both Sec31and Sec13
Which of the following carbohydrates is not synthesized in the Golgi complex? a) glycosaminoglycans in the animal extracellular matrix b) plant cell wall polysaccharides like pectin and hemicellulose c) the carbohydrates of glycolipids d) the carbohydrates of glycoproteins e) glycogen
e) glycogen
A cellular phenomenon called RNA interference is a process in which cells produce small RNAs called _______ that bind to specific mRNAs and inhibit the translation of these mRNAs into proteins. a) snRNAs b) isRNAs c) mRNAs d) RNAsi e) siRNAs
e) siRNAs
What specific cellular responses are known to be triggered by the regulated release of Ca2+ ions from the SER? a) skeletal muscle cell contraction b) secretory vesicle fusion with the plasma membrane c) release of neurotransmitters from nerve cells d) release of the contents of the acrosome from the head of a sperm e) skeletal muscle cell contraction
e) skeletal muscle cell contraction
