Lodish 8e Ch 13 Test Bank PDF

13 *Section 13.1* 1\. Which of the following proteins involved in cotranslational translocation of proteins into the ER membrane is NOT a GTP-hydrolyzing protein? a\. α subunit of the SRP receptor b\. elongation factors in ribosome-mediated mRNA translation c\. P54 subunit of SRP d\. Sec61 tra...

13 *Section 13.1* 1\. Which of the following proteins involved in cotranslational translocation of proteins into the ER membrane is NOT a GTP-hydrolyzing protein? a\. α subunit of the SRP receptor b\. elongation factors in ribosome-mediated mRNA translation c\. P54 subunit of SRP d\. Sec61 translocon Ans: d Question Type: Multiple choice Section 13.1 Blooms: Analyzing Difficulty: Moderate 2\. Protein insertion into the mammalian ER membrane is typically: a\. cotranslational. b\. post-translational. c\. pretranslational. d\. quasitranslational. Ans: a Question Type: Multiple choice Section 13.1 Blooms: Understanding Difficulty: Moderate 3\. Post-translational translocation of some secretory proteins in yeast is powered by: a\. ATP hydrolysis by BiP. b\. cAMP hydrolysis by cAMP phosphodiesterase. c\. GTP hydrolysis EF-Tu. d\. phospholipid hydrolysis by phospholipase C. Ans: a Question Type: Multiple choice Section 13.1 Blooms: Remembering Difficulty: Moderate 4\. In the absence of targeting information, what is the default location of proteins synthesized on cytosolic ribosomes? Ans: Proteins synthesized on cytosolic ribosomes that contain no information for targeting to organelles diffuse throughout the cytosol. Question Type: Essay Section 13.1 Blooms: Understanding Difficulty: Easy 5\. What are the general features of an N-terminal signal sequence that targets secretory proteins to the ER? Ans: N-terminal signal sequences targeting proteins to the ER are 16 to 30 amino acids in length and have a hydrophobic core of 6 to 12 amino acids. Preceding the core is one or more positively charged amino acids. Otherwise, N-terminal signal sequences have little in common. Question Type: Essay Section 13.1 Blooms: Applying Difficulty: Moderate 6\. In a cell-free protein synthesis system utilizing microsomes from fragmented ER, under which condition could you determine if the new protein was imported into the microsome? a\. Ribosomes and mRNA are incubated with microsomes, then a protease is added and the results are analyzed. b\. Ribosomes and mRNA are incubated with microsomes, then a protease and detergent are added and the results are analyzed. c\. Ribosomes and mRNA are incubated with protease, then microsomes are added and the results are analyzed. d\. Ribosomes and mRNA are incubated with microsomes, then detergent is added and the results are analyzed. Ans: a Question Type: Multiple choice Section 13.1 Blooms: Analyzing Difficulty: Moderate 7\. Which of the following is true about ER import? a\. N-terminal signal sequences have been determined to be necessary for ER import because if they are added to sequences which are not normally targeted to the ER, they will end up in the ER. b\. Signal recognition particles (SRPs) are needed during co-translational import. c\. Ribosomal translation of a 6-12 amino acid sequence on the N-terminus will initiate the process through interactions with SRP. d\. GTP hydrolysis by the Sec61 translocon causes ribosomal translation to begin again after it is halted by SRP binding. Ans: c Question Type: Multiple choice Section 13.1 Blooms: Understanding Difficulty: Difficult *Section 13.2* 8\. Type I membrane proteins have all of the following properties, except: a\. cleavable signal sequence. b\. internal signal-anchor sequence. c\. internal stop-transfer sequence. d\. N-out, C-in topology. Ans: b Question Type: Multiple choice Section 13.2 Blooms: Understanding Difficulty: Moderate 9\. GPI-anchoring serves a special function, especially in polarized epithelial cells, because this modification serves to target proteins to the: a\. RER. b\. Golgi. c\. plasma membrane. d\. nucleus. Ans: c Question Type: Multiple choice Section 13.2 Blooms: Understanding Difficulty: Easy 10\. The topology of membrane proteins can often be predicted by computer programs that identify[\_\_\_\_\_] topogenic segments. a\. glycosylation-specific b\. hydrophilic c\. hydrophobic d\. cleavable signal sequence Ans: c Question Type: Multiple choice Section 13.2 Blooms: Understanding Difficulty: Easy 11\. In multipass membrane proteins synthesized in association with membrane-bounded ribosomes of the rough ER, signal-anchor and stop-transfer anchor sequences alternate. What do these sequences do? Ans: Signal-anchor sequences direct insertion of internal segments of the protein into the ER membrane; stop-transfer sequences stop the transfer of the protein across the membrane. The alternation of the two produces a protein that loops in and out of the membrane multiple times. Question Type: Essay Section 13.2 Blooms: Understanding Difficulty: Easy 12\. Having misfolded soluble or secretory proteins in the RER contributes to what investigators call the "traffic jam," a scenario associated with a number of human diseases where the normal transport of proteins is blocked by these abnormal proteins and the inability of protein complexes to arrive at their correct site and function properly. Briefly describe how the cell overcomes this particular traffic jam by exporting the misfolded proteins out of the RER into the cytosol, where they are degraded by the proteasome. Ans: Essentially, the misfolded proteins have N-linked carbohydrate chains that are trimmed by the enzyme α-mannosidase. Once trimmed, these proteins are recognized by the lectin-like protein EDEM and/or OS-9, which targets the protein to an ER-associated degradation or ERAD complex, which serves as a type of channel needed to export the protein into the cytosol. Once in the cytosol, these proteins are subjected to enzymes that eventually target them to the proteasome for degradation. Question Type: Essay Section 13.2 Blooms: Applying Difficulty: Difficult 13\. A transmembrane receptor that functions at the cell membrane has an exoplasmic N-terminal sequence, a signal-anchor sequence, and a stop-transfer-anchor sequence. This protein was first inserted into the membrane where? a\. at the plasma membrane b\. in the cis-Golgi c\. in the late endosome d\. in the ER Ans: d Question Type: Multiple choice Section 13.2 Blooms: Understanding Difficulty: Moderate *Section 13.3* 14\. Glycosylation, a post-translational modification of proteins, occurs in the: a\. Golgi. b\. proteasome. c\. mitochondria. d\. none of the above Ans: a Question Type: Multiple choice Section 13.3 Blooms: Remembering Difficulty: Easy 15\. All the following proteins interact with exposed amino acids during protein folding in the ER, except: a\. BiP. b\. calnexin. c\. PDI. d\. prolyl isomerase. Ans: b Question Type: Multiple choice Section 13.3 Blooms: Remembering Difficulty: Moderate 16\. Unassembled or misfolded proteins in the RER can be damaging to the physiology of a cell and therefore are transported to the cytosol where they are degraded. This transport process is referred to as: a\. polyubiquitination. b\. disulfide isomerization. c\. dislocation. d\. O-linked glycosylation. Ans: c Question Type: Multiple choice Section 13.3 Blooms: Remembering Difficulty: Easy 17\. What is the meaning of "quality control in the ER?" Ans: "Quality control within the ER" refers to the need for proteins to be properly modified and folded before they can exit from the ER and travel to the Golgi apparatus. Improperly modified and folded proteins are typically translocated into the cytosol for degradation. Question Type: Essay Section 13.3 Blooms: Understanding Difficulty: Easy 18\. Why are bacteria often a poor choice for the production of proteins for therapeutic purposes? Ans: Typically, proteins used for therapeutic purposes are secreted proteins in animals; disulfide bonds stabilize their structures. Disulfide-bond formation occurs spontaneously in the lumen of the ER but not within bacteria. With this realization, animal cells became the preferred choice for the production of such proteins. Question Type: Essay Section 13.3 Blooms: Applying Difficulty: Moderate *Section 13.4* 19\. Sorting of proteins to mitochondria and chloroplasts is: a\. cotranslational. b\. post-translational. c\. pretranslational. d\. quasitranslational. Ans: b Question Type: Multiple choice Section 13.4 Blooms: Remembering Difficulty: Moderate 20\. Tom/Tim and Toc/Tic protein complexes are involved in: a\. post-receptor recognition events in the cytosolic folding of proteins prior to import into mitochondria or chloroplasts. b\. pre-proteasomal steps in tagging aged proteins for degradation. c\. protein translocation into mitochondria and chloroplasts, respectively. d\. resetting biological clocks following rounds of intense protein synthesis. Ans: c Question Type: Multiple choice Section 13.4 Blooms: Applying Difficulty: Moderate 21\. Protein sequences for targeting to mitochondria or chloroplasts are located at: a\. the C-terminus of the precursor protein. b\. amino acid position 173 in most mitochondrial and chloroplast proteins. c\. the N-terminus of the precursor protein. d\. the second and third answers are correct Ans: c Question Type: Multiple choice Section 13.4 Blooms: Remembering Difficulty: Moderate 22\. Protein import into the mitochondrial matrix is supported by energy input from: a\. ATP hydrolysis by chaperone proteins in the cytosol. b\. ATP hydrolysis by chaperone proteins in the mitochondrial matrix. c\. the proton-motive force across the inner mitochondrial membrane. d\. all of the above Ans: d Question Type: Multiple choice Section 13.4 Blooms: Understanding Difficulty: Moderate 23\. During in vitro translation of mitochondrially targeted proteins, when must mitochondria be added for import of proteins synthesized on cytosolic ribosomes? Ans: Proteins are imported into mitochondria post-translationally. Therefore, although mitochondria can be added during the translation process for import to occur, cotranslational presence is not a requirement as it is for import into the ER. The mitochondria can be added post-translationally. Question Type: Essay Section 13.4 Blooms: Applying Difficulty: Moderate 24\. How are proteins imported into the thylakoids of chloroplasts? Ans: For cytosolically synthesized proteins targeted to chloroplast thylakoids, multiple N-terminal uptake-targeting sequences are required. These act sequentially with the N-terminus, most targeting sequences being removed in the chloroplast stroma to expose the next targeting sequence. Four different pathways are known for the import of proteins from the chloroplast stroma into thylakoids. Three are for proteins imported from the cytosol and one is for proteins made in the chloroplast stroma. All pathways are variations of those used for export of proteins by bacteria. Examples of proteins homologous between bacteria and chloroplasts have been identified. Question Type: Essay Section 13.4 Blooms: Applying Difficulty: Difficult 25\. A polypeptide chain contains an amphipathic helix, with arginine and lysine residues on one side and hydrophobic residues on the other. It will likely enter: a\. the peroxisome. b\. the ER. c\. the lysosome. d\. the mitochondria. Ans: d Question Type: Multiple choice Section 13.4 Blooms: Remembering Difficulty: Moderate 26\. In a cell that lacks cytosolic Hsc70: a\. import of proteins into the mitochondrial matrix would be diminished. b\. proteins in the ER would not fold properly. c\. the peroxisome would contain more catalase. d\. generation of ATP from the electron transport chain would happen at the plasma membrane. Ans: a Question Type: Multiple choice Section 13.4 Blooms: Applying Difficulty: Moderate 27\. Which of the following components of mitochondrial import are NOT required for a sequence containing a matrix-targeting sequence and an intermembrane-space-targeting sequence? a\. Tom b\. Tim c\. Oxa1 d\. membrane-bound protease Ans: c Question Type: Multiple choice Section 13.4 Blooms: Remembering Difficulty: Moderate *Section 13.5* 28\. Many peroxisomal matrix proteins are imported as: a\. folded proteins. b\. nascent chains in the process of completing their elongation. c\. protein fragments that are spliced together within the peroxisome. d\. unfolded proteins. Ans: a Question Type: Multiple choice Section 13.5 Blooms: Remembering Difficulty: Easy 29\. PTS1- and PTS2-bearing matrix proteins are targeted to: a\. a common cytosolic receptor. b\. a common import receptor and translocation machinery on the peroxisomal membrane. c\. a common receptor on the nuclear pore that catalyzes entry into the nucleus via pore targeting sequences. d\. a common receptor protein within the peroxisomal matrix that activates protein processing for PTS1- and PTS2-bearing proteins. Ans: b Question Type: Multiple choice Section 13.5 Blooms: Remembering Difficulty: Moderate 30\. Unlike mitochondria and chloroplasts, peroxisomes can arise [\_\_\_\_\_] from precursor membranes, as well as by division of preexisting organelles. a\. as condensate b\. as dispersions c\. de novo d\. as vaporware Ans: c Question Type: Multiple choice Section 13.5 Blooms: Understanding Difficulty: Easy 31\. To what extent do peroxisomal matrix protein import and peroxisomal membrane protein import share the same machinery? Ans: The fact that mutated cells giving rise to Zellweger syndrome, a defect in peroxisomal matrix protein import, still form peroxisomal membranes (peroxisomal ghosts) with the normal composition of peroxisomal membrane proteins strongly indicates that the import machinery for membrane proteins is very different from that for matrix proteins. This situation is different from that for other organelles such as the ER, mitochondria, and chloroplasts. Question Type: Essay Section 13.5 Blooms: Applying Difficulty: Moderate 32\. What is meant by de novo formation of peroxisomes? Ans: This is the concept that peroxisomes can arise from nonperoxisomal membranes. The peroxisomal proteins Pex19, Pex3, and Pex16 are involved. The nature of the precursor membrane is unclear. Question Type: Essay Section 13.5 Blooms: Understanding Difficulty: Moderate 33\. Many peroxisomal matrix proteins are imported as: a\. folded proteins. b\. nascent chains in the process of completing their elongation. c\. protein fragments that are spliced together within the peroxisome. d\. unfolded proteins. Ans: a Question Type: Multiple choice Section 13.5 Blooms: Understanding Difficulty: Moderate *Section 13.6* 34\. The nuclear pore complex allows for: a\. passive diffusion of smaller molecules. b\. import of proteins. c\. active transport of very large molecules. d\. all of the above Ans: d Question Type: Multiple choice Section 13.6 Blooms: Understanding Difficulty: Easy 35\. During the import of proteins into the nucleus, the α importin subunit binds directly to: a\. FG nucleoporins. b\. Ran·GDP c\. basic nuclear localization signals in cargo proteins. d\. all of the above Ans: c Question Type: Multiple choice Section 13.6 Blooms: Understanding Difficulty: Moderate 36\. Which type of RNA participates in nuclear export of mRNA? a\. snRNA b\. hnRNA c\. tRNA d\. rRNA Ans: b Question Type: Multiple choice Section 13.6 Remebering Difficulty: Moderate 37\. Which of the following is present in the nuclear export sequence of PKI (an inhibitor of protein kinase A)? a\. a proline-rich sequence b\. a leucine-rich sequence c\. a lysine-rich sequence d\. all of the above Ans: b Question Type: Multiple choice Section 13.6 Remebering Difficulty: Moderate 38\. Transport of unspliced HIV mRNA from the nucleus to the cytoplasm of host cells is promoted by a virus-encoded protein named: a\. Tat. b\. Rev. c\. nucleoplasmin. d\. Ran. Ans: b Question Type: Multiple choice Section 13.6 Remebering Difficulty: Easy 39\. How does Ran·GTP participate in the nuclear export of the HIV Rev protein? Ans: In the nucleus, Ran·GTP binds to the nuclear export receptor exportin 1 and then to the leucine-rich nuclear export sequence (NES) in Rev. Exportin 1, in this trimolecular cargo complex, interacts transiently with FG repeats in FG-nucleoporins, allowing it to traverse the nuclear pore complex (NPC). In the NPC, the cargo complex encounters Ran·GAP, stimulating Ran to hydrolyze GTP, which reduces its affinity for exportin 1. Exportin 1 subsequently loses its affinity for the NES, releasing Rev to the cytoplasm. Question Type: Essay Section 13.6 Blooms: Applying Difficulty: Difficult 40\. The nuclear pore complex (NPC) contains\_\_\_\_\_ structures that form a gel-like matrix that allow small molecules to diffuse through, but require larger proteins to enter via importin or other nuclear chaperones. a\. nuclear localization signals (NLS) b\. nuclear lamina c\. structural nucleoporin d\. FG-nucleoporin Ans: d Question Type: Multiple choice Section 13.6 Blooms: Remembering Difficulty: Easy 41\. During the process of nuclear import, a GEF works in the: a\. cytoplasm to exchange GTP for GDP bound to Ran. b\. cytoplasm to use GTP to release Ran from importin. c\. nucleus to exchange GTP for GDP bound to Ran. d\. nucleus to activate the intrinsic GTPase activity of Ran. Ans: c Question Type: Multiple choice Section 13.6 Blooms: Understanding Difficulty: Moderate