230 Chapter 15

A. cisterna -3 B. Golgi stack - 1 C. secretory vesicle - 5 D. trans Golgi network -4 E. cis Golgi network - 2

1. Match each cellular comparment with the correct label in Figure 15-3. Figure 15-3 A. cisterna B. Golgi stack C. secretory vesicle D. trans Golgi network E. cis Golgi network

d. all of these answers are correct

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 these answers are correct

a. When this vesicle fuses with the plasma membrane, the entire Krt1 protein will be secreted into the extracellular space.

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.

c. in the cytosol

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

1. nucleus - D 2. peroxisome - I 3. rough endoplasmic reticulum - C 4. Golgi apparatus - B 5. cytosol - H 6. endosome - J 7. plasma membrane - E 8. lysosome - G 9. mitochondrion - A 10. free ribosomes - F

Match each cell part with the correct label in Figure 15-1. 1. nucleus 2. peroxisome 3. rough endoplasmic reticulum 4. Golgi apparatus 5. cytosol 6. endosome 7. plasma membrane 8. lysosome 9. mitochondrion 10. free ribosomes

1. signal-recognition particle - A 2. protein translocator - C 3. mRNA - A 4. SRP receptor - C 5. active site of signal peptidase - B

Match the components involved with ER transport with the appropriate cellular location. Locations can be used more than once, or not at all. Location A. cytosol B. ER lumen C. ER membrane Components 1. signal-recognition particle 2. protein translocator 3. mRNA 4. SRP receptor 5. active site of signal peptidase

1. recycled to the original membrane2. destroyed in the lysosome3. transcytosed across the cell to a different membrane

Name three possible fates for an endocytosed molecule that has reached the endosome.

endoplasmic reticulum amino acid sequence folded sorting signal transport vesicles protein translocators unfolded form

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.

a. cytosol.

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the a. cytosol. b. mitochondria. c. interior of the nucleus. d. nuclear membrane.

d. transport vesicles.

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.

c. in the amino acid sequence and sufficient for targeting a protein to its correct destination.

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.

cytosol endosomes lysosome golgi apparatus ER

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.

c. cis Golgi network.

Vesicles from the ER enter the Golgi at the a. medial cisternae. b. trans Golgi network. c. cis Golgi network. d. trans cisternae.

c. Nuclear transport receptors would be unable to release their cargo in the nucleus.

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.

The N-terminal signal sequence initiates translocation and the protein chain starts to thread through the translocation channel. When the stop-transfer sequence enters the translocation channel, the channel discharges both the signal sequence and the stop-transfer sequin sideways into the lipid bilayer. The signal sequence is then cleaved, so that the protein remains held in the membrane by the hydrophobic stop-transfer sequence.

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.

c. begin to cross the membrane while still being synthesized.

Most proteins destined to enter the endoplasmic reticulum a. are transported across the membrane after their synthesis is complete. b. are completely translated on free ribosomes in the cytosol. c. begin to cross the membrane while still being synthesized. d. remain within the endoplasmic reticulum.

The protein would enter the ER. The signal for a protein to enter the ER is recognized as the protein is being synthesized and all end up either in the ER or on the ER membrane. Cystolic nuclear transport proteins recognize proteins destined for the nucleus once those proteins are fully synthesized and fully folded.

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.

a. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.

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.

d. ER → Golgi → plasma membrane

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

c. mitochondria

Which of the following organelles is not part of the endomembrane system? a. Golgi apparatus b. the endosome c. mitochondria d. lysosomes

d. adaptins

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

c. Nuclear pores contain proteins with disordered segments that fill the channel and allow small water-soluble molecules to pass through in a non-selective fashion.

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 contain proteins with disordered segments that fill the channel and allow small water-soluble molecules to pass through in a non-selective fashion. d. Nuclear pores are made up of many copies of a single protein.

a. Phagocytic cells are important in the gut to take up large particles of food.

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.

b. Proteins to be delivered to the ER lumen are synthesized on the smooth ER.

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 the smooth ER. c. Steroid hormones are synthesized on the smooth ER. d. The ER membrane is contiguous with the outer nuclear membrane.

a. Clathrin molecules are important for binding to and selecting cargoes for transport.

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.

c. Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation

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.

c. Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.

Which of the following statements is TRUE? 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.

d. Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.

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.

b. Cytosolic cholesterol levels will decrease relative to normal cells.

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.

c. dynamin

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 was not listening carefully when he was told about the molecular defect of this cell line. He is 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