Lodish 8e Ch14 Test Bank PDF

14 *Section 14.1* 1\. The discovery of green fluorescent protein (GFP) has greatly facilitated living cell experiments because: a\. GFP is green. b\. GFP requires a jellyfish-specific cofactor. c\. GFP sequences may be readily fused to those of other proteins. d\. wild-type GFP folding is adap...

14 *Section 14.1* 1\. The discovery of green fluorescent protein (GFP) has greatly facilitated living cell experiments because: a\. GFP is green. b\. GFP requires a jellyfish-specific cofactor. c\. GFP sequences may be readily fused to those of other proteins. d\. wild-type GFP folding is adapted to normal seawater temperatures, 15--25 °C. Ans: c Question Type: Multiple choice Section 14.1 Blooms: Applying Difficulty: Moderate 2\. Endoglycosidase D is a useful reagent because it allows scientists to distinguish glycosylated proteins that: a\. remain in the *cis*-Golgi. b\. remain in the *trans*-Golgi. c\. remain in the ER. d\. get secreted. Ans: c. Question Type: Multiple choice Section 14.1 Blooms: Understanding Difficulty: Moderate 3\. Yeast *sec* mutations: a\. provide little evidence regarding the mechanism, necessitating other assays or information. b\. invariably affect nonessential genes. c\. affect protein transport into mitochondria but not chloroplasts. d\. all fall into the same complementation class. Ans: a Question Type: Multiple choice Section 14.1 Blooms: Analyzing Difficulty: Moderate 4\. Cell-free transport assays: a\. complement genetic approaches to the secretory pathway. b\. often probe for changes in the glycosylation state of transported proteins. c\. provide a means to test the effect of added purified proteins. d\. all of the above Ans: d Question Type: Multiple choice Section 14.1 Blooms: Understanding Difficulty: Difficult 5\. Why is VSV G protein one of the more useful tools in analyzing membrane trafficking? Ans: The usefulness of VSV G protein resides mainly in its folding properties or, more specifically, those of the mutant VSV G protein, tsO45 G. When expressed in cells, this protein is temperature sensitive in its folding properties. At 39.5 °C, the protein folds abnormally in the endoplasmic reticulum (ER) and fails to exit from the ER. At 32 °C, the protein folds normally and exits the ER. Most important, misfolded VSV G will fold normally when the culture temperature is shifted to 32 °C. This permits a pulse-chase situation in which tsO45 G accumulates in the ER and then may be chased from the ER by a temperature shift in the presence of a protein-synthesis inhibitor to prevent the synthesis of new VSG G. The protein has two N-linked oligosaccharide chains. Therefore, its subcellular distribution may be inferred from its glycosylation state. As a protein, it may be fused to GFP. As a viral protein, high levels of VSV G expression are tolerated by cells. Question Type: Essay Section 14.1 Blooms: Applying Difficulty: Difficult 6\. How can the direction in which vesicles move in a VSV G--based, cell-free system for transport between Golgi compartments be distinguished? Ans: Certainly, the results from such a cell-free system provide strong evidence for transfer between Golgi compartments and the role of various proteins in this transfer. In a cisternal progression context, the results are interpreted to mean that the Golgi enzyme is transported to the compartment containing the cargo protein, VSV G. In other words, a retrograde vesicle is formed by budding from the wild type Golgi, and this retrograde vesicle transports the resident Golgi enzyme *N*-acetylglucosaminyltransferase to the mutant Golgi containing VSV G protein. Using this assay system, vesicles can be isolated, and the composition of the transport vesicles can be characterized. The data indicate that the vesicles are enriched in Golgi enzymes, not VSV G protein. Such data are sufficient to establish that the vesicles are retrograde carriers. Question Type: Essay Section 14.1 Blooms: Analyzing Difficulty: Difficult 7\. The first step in the secretory pathway that should be inhibited by a non-functional mutant of NSF is: a\. ER to Golgi transport. b\. intra-Golgi transport. c\. *trans*-Golgi network (TGN) transport to the plasma membrane. d\. *trans*-Golgi network (TGN) transport to endosomes. Ans: a Question Type: Multiple choice Section 14.1 Blooms: Applying Difficulty: Moderate 8. Given the wild type (normal) yeast on the left and the mutant yeast on the right, identify the defective phenotype for the mutant. a\. entry into the ER b\. fusion of transport vesicles from the ER to the Golgi c\. budding from the Golgi to secretory vesicles d\. fusion of secretory vesicles with the plasma membrane Ans: b Question Type: Multiple choice Section 14.1 Blooms: Understanding Difficulty: Moderate *Section 14.2* 9\. Vesicle budding recruits proteins that are needed for subsequent: a\. invagination of the vesicle into the ER lumen. b\. selective vesicle targeting and fusion. c\. shedding of integral membrane proteins into the cytosol. d\. assembly of chromosome folding machinery. Ans: b Question Type: Multiple choice Section 14.2 Blooms: Applying Difficulty: Moderate 10\. The presence of clathrin mediates vesicular transport: a\. from ER to *cis*-Golgi. b\. *trans*-Golgi to endosome. c\. nuclear membrane to endosome. d\. plasma membrane to *trans*-Golgi. Ans: b Question Type: Multiple choice Section 14.2 Blooms: Remembering Difficulty: Easy 11\. Which of the following small GTPases are NOT involved in vesicle budding or docking? a\. ARF b\. rab1 c\. ras d\. Sar1p Ans: c Question Type: Multiple choice Section 14.2 Blooms: Remembering Difficulty: Moderate 12\. How are different coat proteins recruited to different sites within the cell? Ans: There are three known classes of coat proteins: clathrin, COPI, and COPII. Small GTPases recruit each to membranes. Sar1 recruits COPII. Sar1 itself is activated by a guanine nucleotide exchange factor, Sec12, an ER integral membrane protein. ARF recruits both clathrin and COPII. How ARF, or different isoforms of ARF, and guanine nucleotide exchange factor(s) recruit different coat protein/adapters to different sites is not yet known. Question Type: Essay Section 14.2 Blooms: Applying Difficulty: Difficult 13\. How are SNARE proteins thought to bring about specific membrane fusion? Ans: SNARE proteins are thought to bring about specific membrane fusion by a pairing process. During vesicle budding, v-SNARE proteins are recruited into the budding vesicle membrane. The cytosolic surface of the target membrane expresses exposed t-SNARE proteins. v-SNARE and t-SNARE proteins pair to form coiled-coil complexes, drawing the vesicle and target membranes very close together. Membrane fusion then occurs by a process that is not well understood. Question Type: Essay Section 14.2 Blooms: Applying Difficulty: Moderate 14\. If Sar1 is inserted into the membrane: a\. it is bound to GTP and recruits COPII coat proteins. b\. it is bound to GDP and recruits COPII coat proteins. c\. it is bound to GTP and recruits cargo. d\. it is not bound to GTP or GDP. Ans: a Question Type: Multiple choice Section 14.2 Blooms: Understanding Difficulty: Easy 15\. Proteins that function in the ER will encounter which of the following? a\. enzymatic modification of the ER resident soluble protein to add the KDEL sequence b\. release from KDEL receptor binding in the Golgi due to a pH change c\. anterograde transport in COPII coated vesicles d\. sequestration in the ER by KDEL receptors Ans: c Question Type: Multiple choice Section 14.2 Blooms: Understanding Difficulty: Moderate 16\. What phenotype would be observed in a cell containing a nonhydrolyzable form of ATP with respect to the vesicles of the secretory pathway? a\. Secretion of peptides from the cell would be increased. b\. Vesicles would be delivered to incorrect target membranes. c\. Uncoated vesicles would accumulate. d\. Coated vesicles would accumulate. Ans: d Question Type: Multiple choice Section 14.2 Blooms: Analyzing Difficulty: Moderate *Section 14.3* 17\. COPI coat proteins mediate [ ] transport between the Golgi apparatus and other organelles. a\. anterograde b\. enterograde c\. retrograde d\. siderograde Ans: c Question Type: Multiple choice Section 14.3 Blooms: Remembering Difficulty: Easy 18\. Which of the following is a forward transport sorting signal acting at the ER? a\. diacidic amino acid motif within the cytosolic domain b\. KDEL (Lys-Asp-Glu-Leu) C-terminal sequence c\. KKXX (Lys-Lys-X-X) within the cytosolic domain d\. NPXY (Asn-Pro-X-Tyr) within the cytosolic domain Ans: a Question Type: Multiple choice Section 14.3 Blooms: Remembering Difficulty: Easy 19\. Soluble and membrane proteins advance through the Golgi complex by: a\. cisternal progression. b\. stable continuities between Golgi cisterna. c\. transient continuities between Golgi cisterna. d\. vesicular transport. Ans: a Question Type: Multiple choice Section 14.3 Blooms: Understanding Difficulty: Moderate 20\. What is the role of vesicles in the early stages of the secretory pathway such as ER to Golgi trafficking? Ans: There are two classes of coat proteins involved in the early stages of the secretory pathway. COPII coat proteins are involved in vesicle budding at the ER. The newly formed COPII-coated vesicles act as anterograde (forward) carriers. COPI coat proteins are involved in vesicle budding at the *cis*-Golgi network and within the Golgi. COPI vesicles mediate retrograde (backward) traffic that recycles soluble and membrane proteins to their site of residence. Question Type: Essay Section 14.3 Blooms: Applying Difficulty: Easy 21\. How are soluble, luminal ER proteins that "leak" out of the ER retrieved to the ER? Ans: Soluble proteins of the ER have a Lys-Asp-Glu-Leu (KDEL) amino acid sequence in their C-terminus. This sequence is a retrieval signal. ER-resident proteins that are missorted to the *cis*-Golgi network bind to a KDEL receptor located in the cis-Golgi network. The missorted ER-resident protein KDEL receptor complex is recognized by COPI coat proteins and carried back to the ER via retrograde COPI vesicles. Question Type: Essay Section 14.3 Blooms: Understanding Difficulty: Moderate *Section 14.4* 22\. Protein sorting of anterograde cargo to different destinations within the Golgi complex occurs in the: a\. *cis-*Golgi. b\. *medial-*Golgi. c\. *trans*-Golgi. d\. *trans-*Golgi network. Ans: d Question Type: Multiple choice Section 14.4 Blooms: Understanding Difficulty: Easy 23\. In hepatocytes, the process by which apically destined proteins travel from the basolateral region across the cell before fusing with the apical membrane is called: a\. exocytosis. b\. transcytosis. c\. endocytosis. d\. none of the above Ans: b Question Type: Multiple choice Section 14.4 Blooms: Remembering Difficulty: Easy 24\. The mannose 6-phosphate residue is important, as it is required to target soluble enzymes to the lysosome. The two enzymes responsible for attaching this residue onto these soluble enzymes reside in the: a\. RER. b\. *cis*-Golgi. c\. *medial*-Golgi. d\. *trans*-Golgi. Ans: b Question Type: Multiple choice Section 14.4 Blooms: Remembering Difficulty: Moderate 25\. In MDCK cells, which of the following is a sorting signal that allows proteins to be targeted to the apical membrane? a\. GPI b\. HA c\. KDEL d\. all of the above Ans: a Question Type: Multiple choice Section 14.4 Blooms: Remembering Difficulty: Easy 26\. How are clathrin-coated vesicles pinched off? Ans: Clathrin-coated vesicles are pinched off in a dynamin-mediated process. Dynamin is a cytosolic GTPase that forms a collar around the necks of clathrin-coated buds. It forces the neck membranes close together and membrane fusion (i.e., pinching off) occurs. The GTPase activity is necessary for this. Question Type: Essay Section 14.4 Blooms: Understanding Difficulty: Moderate 27\. Professor George Palade's elegant experiment to follow protein synthesis and trafficking, published nearly 60 years ago, provided us with a great deal of information and has been used as a tool by several investigators. If you had access to all the reagents needed to repeat the in vitro experiment, describe what you would need to do to see the progression of newly synthesized proteins and their transport in the cell. Ans: Expose pancreatic tissue slices to radioactive leucine for a short period of time (referred to as a pulse). The radioactive pulse of leucine will then be replaced with nonradioactive leucine (the chase), and at varying time points the slices will be fixed and processed for electron microscopy and autoradiography. Autoradiographs of tissue sections will be compared to electron microscopy images to visualize the location of radioactive granules in the cell. At time points shortly after the chase begins, granules should be visualized in the ER, but at later "post-chase" time points the granules would be in the Golgi or near the plasma membrane. Question Type: Essay Section 14.4 Creating Difficulty: Moderate *Section 14.5* 28\. The LDL receptor is a receptor for: a\. apolipoprotein B. b\. receptor-mediated endocytosis of LDL. c\. cell signaling via activation of adenylate cyclase. d\. apolipoprotein B and receptor-mediated endocytosis of LDL. Ans: d Question Type: Multiple choice Section 14.5 Blooms: Understanding Difficulty: Easy 29\. Lipoproteins are effective in transporting lipid molecules in an aqueous environment because their surface layer is: a\. hydrophobic. b\. glycosidic. c\. amphipathic. d\. hydrophobic and glycosidic. Ans: c Question Type: Multiple choice Section 14.5 Blooms: Understanding Difficulty: Moderate 30\. Acidification of endosomes is important in dissociating: a\. cholesterol from LDL. b\. iron from transferrin. c\. transferrin from the transferrin receptor. d\. all of the above Ans: b Question Type: Multiple choice Section 14.5 Blooms: Understanding Difficulty: Moderate 31\. Formation of the late endosome/multivesicular endosome occurs by mechanisms similar to those of: a\. exocytosis of insulin in response to glucose levels in the blood. b\. GCA protein--mediated budding at the *trans*-Golgi network. c\. retrovirus budding from the plasma membrane. d\. none of the above Ans: c Question Type: Multiple choice Section 14.5 Blooms: Understanding Difficulty: Moderate 32\. Describe the types of mutations in the LDL receptor that would cause familial hypercholesterolemia. Ans: A mutation that prevents the synthesis of the LDL receptor protein would block LDL uptake. Likewise, mutations that prevent the proper folding of the receptor in the endoplasmic reticulum would lead to its premature degradation. Mutations that interfere or reduce the receptor's ability to bind LDL would also contribute to the disease. Finally, a mutation in the NPXY-sorting signal, which has no apparent effect on receptor-ligand interaction, would block the incorporation of the LDL-LDL receptor into coated pits, thereby preventing internalization. Question Type: Essay Section 14.5 Blooms: Applying Difficulty: Difficult 33\. Which portion of a clathrin coat recognizes internalization signals such as Leu-Leu, Asn-Pro-X-Tyr, and Tyr-X-X-Φ in the cytosolic domain of cell-surface endocytic receptors? Ans: Adapter proteins of the AP2 class recognize internalization signals located within the cytosolic domain of cell-surface endocytic proteins. Adapter proteins associate directly with the plasma membrane. The clathrin triskelion then associates with the adapter proteins. Overall, the complex forms a clathrin/AP2-coated vesicle. Question Type: Essay Section 14.5 Blooms: Understanding Difficulty: Moderate 34\. What is autophagy? Ans: Autophagy ("eating oneself") is the delivery of bulk amounts of cytosol or entire organelles to lysosomes with subsequent degradation. Autophagy is often a regulated process and is typically induced in cells placed under conditions of starvation or other types of stress. The autophagic process begins with the formation of a cup-shaped membrane structure that envelops a portion of the cytosol or an organelle. The source of this membrane is not clear. Question Type: Essay Section 14.5 Blooms: Understanding Difficulty: Moderate 35\. An important molecule for generating fatty acids in the cell enters via receptor-mediated endocytosis. The complex formed between the receptor on the plasma membrane and the important molecule is stable only at neutral pH. Based on this knowledge, you would predict: a\. a COPII-coated vesicle will be required for import. b\. the important molecule enters the cell via a protein channel. c\. *both* the molecule and the receptor are degraded to release the molecule from the receptor. d\. the molecule is released from the receptor in the endosome. Ans: c Question Type: Multiple choice Section 14.5 Blooms: Applying Difficulty: Moderate 36\. The topogenic sequence of transferrin must include: a\. a signal sequence and an internal signal-anchor sequence. b\. an internal signal-anchor sequence with positive charges N-terminal to the SA. c\. an internal signal-anchor sequence with positive charges C-terminal to the SA. d\. alternating signal-anchor sequences with stop-transfer sequences. Ans: b Question Type: Multiple choice Section 14.5 Blooms: Applying Difficulty: Difficult 37\. Receptor-mediated endocytosis of iron-carrying transferrin results in: a\. release of iron and proteolysis of the transferrin protein for recycling inside the cell. b\. transferrin/transferrin receptor complexes in the cytosol of the cell. c\. release of iron from the endosome to the cytosol. d\. vesicle formation at the plasma membrane mediated by COP proteins. Ans: d Question Type: Multiple choice Section 14.5 Blooms: Understanding Difficulty: Moderate *Section 14.6* 38\. The mannose 6-phosphate residue is important, as it is required to target soluble enzymes to the\_\_\_\_\_\_\_\_\_\_. The two enzymes responsible for attaching this residue onto these soluble enzymes reside in the \_\_\_\_\_\_\_\_\_\_\_\_. a\. peroxisome; RER b\. lysosome; *cis*-Golgi c\. nucleus; *medial*-Golgi d\. endosome; *trans*-Golgi Ans: b Question Type: Multiple choice Section 14.6 Blooms: Remembering Difficulty: Moderate 39\. Which of the following is TRUE about lysosomes? a\. They contain enzymes only capable of breaking down nucleic acids. b\. They are bound by a single membrane but can engulf organelles containing double membranes. c\. Proteins targeted to the lysosome are glycosylated in the ER and a specific mannose is phosphorylated. d\. The final, functional state of lysosomal enzymes contains mannose-6-phosphate. Ans: b Question Type: Multiple choice Section 14.6 Blooms: Understanding Difficulty: Moderate