Chapter 15 Test Bank, Chapter 16 Test Bank
16-22 Which of the following statements is true?
(a) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.
15-2 Which of the following statements about membrane-enclosed organelles is true?
(a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane.
15-21 Which of the following statements about peroxisomes is false?
(a) Most peroxisomal proteins are synthesized in the ER.
16-23 Which of the following statements about molecular switches is false?
(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.
16-62 When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is true?
(a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras.
16-60 The ethylene response in plants involves a dimeric transmembrane receptor. When the receptor is not bound to ethylene, the receptor binds to and activates a protein kinase, which activates an intracellular signaling pathway that leads to the degradation of a transcriptional regulator important for transcribing the ethylene-responsive genes (see Figure Q16-60). You discover a phosphatase that is important for ethylene signaling, and you name it PtpE. Plants lacking PtpE never turn on ethylene-responsive genes, even in the presence of ethylene. You find that PtpE dephosphorylates serine 121 on the transcriptional regulator. Furthermore, plants lacking PtpE degrade the transcriptional regulator in the presence of ethylene. Which of the following statements is inconsistent with your data?
(a) When the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-responsive genes.
16-32 Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in Figure Q16-32. Which of the following would enhance this effect of the acetylcholine?
(a) addition of a high concentration of a nonhydrolyzable analog of GTP
16-49 Which of the following mechanisms is not directly involved in inactivating an activated RTK?
(a) dephosphorylation by serine/threonine phosphatases
15-16 A large protein that passes through the nuclear pore must have an appropriate _________.
(a) sorting sequence, which typically contains the positively charged amino acids lysine and arginine.
16-38 Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. Figure Q16-38 shows how G proteins can indirectly activate PKC. You have discovered the enzyme activated by PKC that mediates the lipid modification. You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells lacking Rafty do not have these modifications, even when PKC is active. Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty?
(a) the expression of a constitutively active phospholipase C
16-15 Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false?
(b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family.
15-51 Which of the following statements about the protein quality control system in the ER is false?
(b) Proteins that are misfolded are degraded in the ER lumen.
16-18 Figure Q16-18 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine?(a) a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO
(b) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP
16-52 Male cockroaches with mutations that strongly decrease the function of an RTK called RTKX are oblivious to the charms of their female comrades. This particular RTK binds to a small molecule secreted by sexually mature females. Most males carrying loss-of-function mutations in the gene for Ras protein are also unable to respond to females. You have just read a paper in which the authors describe how they have screened cockroaches that are mutant in RTKX for additional mutations that partly restore the ability of males to respond to females. These mutations decrease the function of a protein that the authors call Z. Which of the following types of protein could Z be? Explain your answer.
(b) a protein that stimulates hydrolysis of GTP by the Ras protein
15-39 Molecules to be packaged into vesicles for transport are selected by
(b) adaptins.
16-50 You are interested in further understanding the signal transduction pathway that controls the production of Pig1, a protein important for regulating cell size. Activation of the TRK receptor leads to activation of the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE transcription factor. SZE only interacts with the nuclear transport receptor when it is phosphorylated. SZE is a gene activator for the Pig1 gene. This pathway is diagrammed in Figure Q16-50.Normal cells grown under standard conditions (without ligand) are 14 μm in diameter while normal cells exposed to TRK ligand are 10.5 μm in diameter. Given this situation, which of the following conditions do you predict will more likely lead to smaller cells?
(b) addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE
16-57 The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________.
(b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.
16-5 When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________.
(b) hormone.
15-52 Which of the following statements about the unfolded protein response (UPR) is false?
(c) Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins.
16-61 Figure Q16-61 shows that intracellular signaling pathways can be highly interconnected.From the information in Figure Q16-61, which of the following statements is incorrect?
(c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active.
15-19 Which of the following statements is true?
(c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.
15-15 Which of the following statements about nuclear transport is true?
(c) Nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a nonselective fashion.
15-18 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?
(c) Nuclear transport receptors would be unable to release their cargo in the nucleus.
15-57 Figure Q15-57 shows the orientation of the Krt1 protein on the membrane of a Golgi-derived vesicle that will fuse with the plasma membrane. Given this diagram, which of the following statements is true?
(c) When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space.
16-35 You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted in Figure Q16-35. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainy transcription?
(c) a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive
16-45 The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation?
(c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
16-63 Figure Q16-63 shows how normal signaling works with a Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line?
(c) addition of a drug that blocks protein Y from interacting with its target
15-23 Most proteins destined to enter the endoplasmic reticulum _________.
(c) begin to cross the membrane while still being synthesized.
15-54 Vesicles from the ER enter the Golgi at the ______.
(c) cis Golgi network.
15-41 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 wasn't listening carefully when he was told about the molecular defect of this cell line. He's 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?
(c) dynamin
15-6 Which of the following organelles is not part of the endomembrane system?
(c) mitochondria
15-47 Which of the following statements about disulfide bond formation is false?
(d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing.
15-36 Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels?
(d) ER í Golgi í plasma membrane
16-58 Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2, as diagrammed in Figure Q16-58. Which of the following statements is false?
(d) In the absence of a survival signal, Bad is phosphorylated.
15-10 Where are proteins in the chloroplast synthesized?
(d) in both the cytosol and the chloroplast
16-31 The length of time a G protein will signal is determined by _______.
(d) the GTPase activity of Gα
15-45 N-linked oligosaccharides on secreted glycoproteins are attached to
(d) the asparagine in the sequence Asn-X-Ser/Thr.
proteins that are not translated do not end up in
(d) transport vesicles.
15-31 Figure Q15-31 shows the organization of a protein that resides on the ER membrane. The N- and C-termini of the protein are labeled. Boxes 1, 2, and 3 represent membrane-spanning sequences. Non-membrane-spanning regions of the protein are labeled "X," "Y," and "Z."
A
16-59 The last common ancestor to plants and animals was a unicellular eukaryote. Thus, it is thought that multicellularity and the attendant demands for cell communication arose independently in these two lineages. This evolutionary viewpoint accounts nicely for the vastly different mechanisms that plants and animals use for cell communication. Fungi use signaling mechanisms and components that are very similar to those used in animals. Which of the phylogenetic trees shown in Figure Q16-59 does this observation support?
B
15-20 Which of the following statements about transport into mitochondria and chloroplasts is false?
B. After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane.
15-29 Which of the following statements is true?
C Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation.
15-28 Which of the following statements about a protein in the lumen of the ER is false? (a) A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane. (b) Some of the proteins in the lumen of the ER can end up in the extracellular space. (c) Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system. (d) Some of the proteins in the lumen of the ER can end up in the plasma membrane.
D
16-11 All members of the steroid hormone receptor family __________________. (a) are cell-surface receptors. (b) do not undergo conformational changes. (c) are found only in the cytoplasm. (d) interact with signal molecules that diffuse through the plasma membrane.
D
15-24 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?
D. (d) all of the above
15-25 In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?
D. cytosol
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