QUIZ PDF - Cell Compartmentalization, Proteins, and Trafficking

Questions and Problems #4 Cell compartmentalization Protein trafficking Endoplasmic reticulum and the Golgi apparatus Topology considers the configuration, arrangement, and positioning of components in cell compartments. Topologically equivalent spaces...

Questions and Problems #4 Cell compartmentalization Protein trafficking Endoplasmic reticulum and the Golgi apparatus Topology considers the configuration, arrangement, and positioning of components in cell compartments. Topologically equivalent spaces are in red. The lumens of many organelles communicate with each other and the extracellular space (e.g., via transport vesicles). Transport destinations are marked with blue arrows. Some organelles (e.g., mitochondria) do not participate in this communication. The inside nuclear compartment is topologically equivalent to the cytosol because the two nuclear membranes are in continuity where the pores are. Furthermore, during cell division, the nuclear content mixes with the cytosol. However, note that the ER lumen is continuous with the space between the inner and outer nuclear membranes, and the ER membrane is continuous with the outer membrane of the nuclear envelope. Thus, the ER lumen and the space between the inner and outer nuclear membranes are topologically equivalent to the extracellular space. From Molecular Biology of the Cell. Alberts B, Johnson A, Lewis J, et al. New York: Garland Science. Keep building your glossary. In our lectures, we use interchangeable terms such as targeting signal, signal sequence, localization signal, and signal. The N-terminal localization signal of proteins that are synthesized on ER-bound ribosomes is also referred to as a signal peptide. 1. While watching the Yankees game in the lab, you accidentally mutate the nuclear localization signal sequence of the large protein Moose 2, rendering the sequence not functional. Which of the following observations do you expect? A. Moose 2 can bind importin. B. Moose 2 is localized in the cytosol. C. Moose 2 is localized in the nucleus. D. Moose 2 is unable to bind to other proteins. 2. An intracellular organelle is observed to release through pores a type of protein into the cytosol. Following this release, biochemical reactions take place and result in the cell’s death by apoptosis. The most likely identity of this organelle is _____. A. the Golgi complex B. a lysosome C. a mitochondrion D. the nucleus 3. Mitochondrial DNA is: I. circular II. self-replicating III. single-stranded A. I only B. II only C. I and II only D. I, II, and III 4. The side of the Golgi stack, at which material from the endoplasmic reticulum (ER) enters the Golgi apparatus is referred to as ______. A. a maturating stack B. the cis side C. the trans side D. None of the above. 5. Which organelle(s) is the next stop in the normal trafficking of a protein exiting the endoplasmic reticulum (ER)? A. the Golgi complex B. the lysosomes C. the mitochondria D. the peroxisomes 6. Which of the following is not a function of the smooth endoplasmic reticulum? A. Lipid synthesis B. Poison detoxification C. Protein synthesis D. Transport of proteins 7. In which of the following locations might a protein that enters the lumen of the endoplasmic reticulum also be found? A. In the cytosol B. In the nucleus C. In peroxisomes D. Outside the cell 8. Association of ribosomes with the endoplasmic reticulum requires ___. I. signal-recognition particle II. chaperones III. protein translation A. I B. I and III C. II and III D. I, II, and III 9. Protein-sorting signal that consists of a specific three-dimensional arrangement of the folded protein’s surface is called ______. A. a signal peptidase B. a signaling sequence C. a signaling patch D. a hydrophobic transmembrane region 10. Dr. Frankenstein has just discovered a novel protein X. The protein functions in the cytosol; therefore, to reach its destination after synthesis, protein X requires _____. A. a signaling sequence B. a signaling patch C. a hydrophobic transmembrane region D. None of the above. 11. ____ is a protein sorting signal that consists of a short continuous sequence of amino acids. A. A signal peptidase B. A signaling sequence C. A signaling patch D. A hydrophobic transmembrane region 12. A cytosolic cellular structure with two subunits is observed to assemble and disassemble, bind to mRNA, and at times, bind to the endoplasmic reticulum. The most likely identity of this structure is a _____. A. Golgi complex B. lysosome C. nucleus D. ribosome 13. A ribosome bound to the endoplasmic reticulum is involved in translating a new protein. The destination, where this new protein functions, is likely to be _______. A. the cytosol B. a lysosome C. a mitochondrion D. the nucleus 14. The intended destination of a newly synthesized protein is the peroxisomes. However, the peroxisomal targeting signal is not properly incorporated into the precursor protein. Therefore, the modified protein will end up ______. A. in the cytosol B. in a lysosome C. in a mitochondrion D. outside the cell 15. True or false? The biological membranes that partition the cell into functionally distinct compartments are impermeable. 16. True or false? The one strict requirement for the exit of a protein from the ER to continue its regular pathway through the Golgi apparatus is to be folded correctly. 17. Which of the following polypeptides is expected to lack any localization (targeting) signal during their synthesis/localization? A. Collagen, an extracellular protein B. Glycophorin, a transmembrane protein C. Ribosomal proteins that assemble with ribosomal RNAs in the nuclei D. None of the above 18. A single membrane-enclosed organelle is observed to be in proximity to the plasma membrane. It appears to surround newly modified proteins in membrane-enclosed structures for delivery to several locations. The most likely identity of this organelle is _____. A. the Golgi complex B. a lysosome C. a mitochondrion D. the nucleus 19. What modifications are made in proteins as they move through the Golgi complex? A. Amino acids are added to either end of a polypeptide chain. B. Amino acids in the proteins are chemically altered into nucleic acids. C. Small segments of amino acids are inserted into the center of an existing protein. D. The protein's oligosaccharides are modified by enzymatic reactions. 20. The guanine nucleotide exchange factors (GEFs) are proteins that ____. A. inactivate small GTPases by stimulating the release of guanosine diphosphate (GDP) to allow the binding of guanosine triphosphate (GTP) B. activate small GTPases by catalyzing the hydrolysis of GTP to GDP C. inactivate small GTPases by catalyzing the hydrolysis of GTP to GDP D. activate small GTPases by stimulating the release of GDP to allow the binding of GTP 21. Indicate true (T) and false (F) statements below regarding the nucleus and nuclear protein transport. Your answer would be a three-letter string composed of letters T and F only, e.g., TTF. ( ) The outer nuclear membrane is studded with ribosomes engaged in protein synthesis. ( ) The inner and outer nuclear membranes are continuous with each other, yet maintain distinct protein compositions ( ) Ribosomal proteins pass through the nuclear pore complexes twice; they are imported into the nucleus after synthesis, and are exported from the nucleus after assembly with ribosomal RNA. A. TFT B. TTT C. FFF D. TTF 22. The "quality control" function of the endoplasmic reticulum (ER) refers to the _________. A. inhibition of ER-entry of proteins that function in organelles such as mitochondria and peroxisomes B. selective transport from ER to Golgi of proteins that require complex glycosylation C. ER-retention of proteins that are incorrectly folded or misfolded D. addition of N‐linked oligosaccharides to lysosomal hydrolase precursors but not to secretory proteins 23. The common pathway of entry into the endoplasmic reticulum (ER) of newly synthesized secretory, lysosomal, endosomal, and integral plasma membrane proteins is explained by the ____________. A. addition of a common sorting signal to each type of protein after completion of synthesis B. addition of oligosaccharides to all the listed types of proteins C. presence of an N-terminal signal sequence that targets each type of protein to the ER during synthesis D. binding to a special class of ribosomes permanently bound to the ER 24. Localization signals that allow large proteins to enter the nucleus are ______. A. added to proteins through post-translational modification B. added to proteins by the protein translocators C. formed by protein sequences of specific amino acid residues D. removed once the proteins are inside the nucleus