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?

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?

(a) In the presence of a survival signal, Akt is phosphorylated.
(b) In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2.
(c) In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active.
(d) In the absence of a survival signal, Bad is phosphorylated.


Answer: D

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________.

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________.

(a) activate the RTK.
(b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.
(c) directly phosphorylate Akt.
(d) to create DAG.


Answer: 

Which of the following statements is true?

Which of the following statements is true?

(a) MAP kinase is important for phosphorylating MAP kinase kinase.
(b) PI 3-kinase phosphorylates a lipid in the plasma membrane.
(c) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP.
(d) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription.

Answer: 

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.

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.

(a) a protein that activates the Ras protein by causing Ras to exchange GDP for GTP
(b) a protein that stimulates hydrolysis of GTP by the Ras protein
(c) an adaptor protein that mediates the binding of the RTKX to the Ras protein
(d) a transcriptional regulator required for the expression of the Ras gene

Answer: 

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?

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?

(a) addition of TRK ligand and a drug that stimulates the GTPase activity of Ras
(b) addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE
(c) addition of TRK ligand and a drug that stimulates the degradation of Pig1
(d) addition of TRK ligand and a drug that inhibits Pig1 binding to DNA

Answer: 

Which of the following mechanisms is not directly involved in inactivating an activated RTK?

Which of the following mechanisms is not directly involved in inactivating an activated RTK?

(a) dephosphorylation by serine/threonine phosphatases
(b) dephosphorylation by protein tyrosine phosphatases
(c) removal of the RTK from the plasma membrane by endocytosis
(d) digestion of the RTK in lysosomes

Answer: 

A protein kinase can act as an integrating device in signaling if it ___________________.

A protein kinase can act as an integrating device in signaling if it ___________________.

(a) phosphorylates more than one substrate.
(b) catalyzes its own phosphorylation.
(c) is activated by two or more proteins in different signaling pathways.
(d) initiates a phosphorylation cascade involving two or more protein kinases.

Answer: 

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization?

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization?

(a) a mutation that increases the affinity of RGFR for RGF
(b) a mutation that prevents RGFR from binding to RGF
(c) changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines
(d) changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid

Answer: 

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?

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?

(a) a mutation that prevents dimerization of the receptor
(b) a mutation that destroys the kinase activity of the receptor
(c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
(d) a mutation that prevents the binding of the normal extracellular signal to the receptor

Answer: 

You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells?

You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells?

(a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive
(b) addition of a drug that prevents GTP hydrolysis by Ga
(c) addition of a drug that activates adenylyl cyclase
(d) addition of a drug that mimics the ligand of ERC1

Answer: 

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?

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
(b) a mutation in the GPCR that binds the signal more tightly
(c) a Ca2+ channel in the endoplasmic reticulum with an increased affinity for IP3
(d) a mutation in the gene that encodes Rafty such that the enzyme can no longer be phosphorylated by PKC

Answer: 

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure Q16-36.Which of the following statements is false?

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure Q16-36.Which of the following statements is false?

(a) A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase.
(b) A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor.
(c) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available.
(d) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.

Answer: 

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?

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?

(a) a mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA
(b) a mutation in the nuclear import sequence of PKA from PPKKKRKV to PPAAAAAV
(c) a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive
(d) a mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the a subunit of the G protein

Answer: 

During the mating process, yeast cells respond to pheromones secreted by other yeast cells. These pheromones bind GPCRs on the surface of the responding cell and lead to the activation of G proteins inside the cell. When a wild-type yeast cell senses the pheromone, its physiology changes in preparation for mating: the cell stops growing until it finds a mating partner. If yeast cells do not undergo the appropriate response after sensing a pheromone, they are considered sterile. Yeast cells that are defective in one or more components of the G protein have characteristic phenotypes in the absence and presence of the pheromone, which are listed in Table 16-34.Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer.

During the mating process, yeast cells respond to pheromones secreted by other yeast cells. These pheromones bind GPCRs on the surface of the responding cell and lead to the activation of G proteins inside the cell. When a wild-type yeast cell senses the pheromone, its physiology changes in preparation for mating: the cell stops growing until it finds a mating partner. If yeast cells do not undergo the appropriate response after sensing a pheromone, they are considered sterile. Yeast cells that are defective in one or more components of the G protein have characteristic phenotypes in the absence and presence of the pheromone, which are listed in Table 16-34.Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer.

(a) a activates the mating response but is inhibited when bound to ß?
(b) ß? activates the mating response but is inhibited when bound to a
(c) the G protein is inactive; either free a or free ß? complex is capable of activating the mating response
(d) the G protein is active; both free a and free ß? complex are required to inhibit the mating response

Answer: 

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?

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
(b) addition of a drug that prevents the a subunit from exchanging GDP for GTP
(c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine
(d) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein

Answer: 

The length of time a G protein will signal is determined by _______.

The length of time a G protein will signal is determined by _______.

(a) the activity of phosphatases that turn off G proteins by dephosphorylating Ga.
(b) the activity of phosphatases that turn GTP into GDP.
(c) the degradation of the G protein after Ga separates from Gß?
(d) the GTPase activity of Ga

Answer: 

Which of the following statements about G-protein-coupled receptors (GPCRs) is false?

Which of the following statements about G-protein-coupled receptors (GPCRs) is false?

(a) GPCRs are the largest family of cell-surface receptors in humans.
(b) GPCRs are used in endocrine, paracrine, and neuronal signaling.
(c) GPCRs are found in yeast, mice, and humans.
(d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

Answer: 

The following happens when a G-protein-coupled receptor activates a G protein.

The following happens when a G-protein-coupled receptor activates a G protein.

(a) The ß subunit exchanges its bound GDP for GTP.
(b) The GDP bound to the a subunit is phosphorylated to form bound GTP.
(c) The a subunit exchanges its bound GDP for GTP.
(d) It activates the a subunit and inactivates the ß? complex.

Answer: 

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____.

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____.

(a) killing cells immediately, exerting their physiological effects by causing cell death.
(b) diffusing through cell plasma membranes and binding to transcription factors to change gene expression.
(c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus.
(d) removing cell-surface receptors from the plasma membrane.

Answer: 

Which of the following statements about molecular switches is false?

Which of the following statements about molecular switches is false?

(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.
(b) Protein kinases transfer the terminal phosphate from ATP onto a protein.
(c) Serine/threonine kinases are the most common types of protein kinase.
(d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.

Answer: 

Which of the following statements is true?

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.
(b) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol.
(c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response.
(d) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.

Answer: 

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?

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
(c) a muscle cell that has cyclic GMP phosphodiesterase constitutively active
(d) a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO

Answer: 

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________.

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________.

(a) activating a G protein.
(b) activating a receptor tyrosine kinase.
(c) diffusing into cells and stimulating the cyclase directly.
(d) activating an intracellular protein kinase.

Answer: 

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?

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?

(a) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract.
(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.
(c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways.
(d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.

Answer: 

The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true?

The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true?

(a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells.
(b) Glial cells do not have a receptor for QGF.
(c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.
(d) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.

Answer: 

All members of the steroid hormone receptor family _________.

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.

Answer: 

Which of the following statements is false?

Which of the following statements is false?

(a) Nucleotides and amino acids can act as extracellular signal molecules.
(b) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription.
(c) Some signal molecules are transmembrane proteins.
(d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.

Answer: 

Which of the following statements is true?

Which of the following statements is true?

(a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal.
(b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.
(c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism.
(d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.

Answer: 

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in ______________ signaling.

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in ______________ signaling.

(a) endocrine
(b) paracrine
(c) neuronal
(d) contact-dependent

Answer: 

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________.

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________.

(a) neurotransmitter.
(b) hormone.
(c) dissolved gas.
(d) scaffold.

Answer: 

Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F is known to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell line B does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques. You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in Table Q16-1.Which of the following cannot be concluded from your results above?

Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F is known to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell line B does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques. You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in Table Q16-1.Which of the following cannot be concluded from your results above?

(a) Binding of factor F to its receptor is required for proliferation of cell line A.
(b) Receptor R binds to factor F to induce cell proliferation in cell line A.
(c) Cell line A expresses a receptor for factor F.
(d) Factor F is not required for proliferation in cell line B.

Answer: 

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?

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.

Answer: 

Which of the following statements about phagocytic cells in animals is false?

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.

Answer: 

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?

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?

(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.

Answer: 

Which of the following statements about secretion is true?

Which of the following statements about secretion is true?

(a) The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior.
(b) Vesicles for regulated exocytosis will not bud off the trans Golgi network until the appropriate signal has been received by the cell.
(c) The signal sequences of proteins destined for constitutive exocytosis ensure their packaging into the correct vesicles.
(d) Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH of the trans Golgi network.

Answer: 

Vesicles from the ER enter the Golgi at the ______.

Vesicles from the ER enter the Golgi at the ______.

(a) medial cisternae.
(b) trans Golgi network.
(c) cis Golgi network.
(d) trans cisternae.

Answer: 

Which of the following statements about the unfolded protein response (UPR) is false?

Which of the following statements about the unfolded protein response (UPR) is false?

(a) Activation of the UPR results in the production of more ER membrane.
(b) Activation of the UPR results in the production of more chaperone proteins.
(c) Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins.
(d) Activation of the UPR results in the cytoplasmic activation of gene regulatory proteins.

Answer: 

Which of the following statements about the protein quality control system in the ER is false?

Which of the following statements about the protein quality control system in the ER is false?

(a) Chaperone proteins help misfolded proteins fold properly.
(b) Proteins that are misfolded are degraded in the ER lumen.
(c) Protein complexes are checked for proper assembly before they can exit the ER.
(d) A chaperone protein will bind to a misfolded protein to retain it in the ER.

Answer: 

Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true?

Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true?

(a) Extensive modification of oligosaccharides occurs in the extracellular space.
(b) Different oligosaccharides are covalently linked to proteins in the ER and the Golgi.
(c) A diversity of oligosaccharyl transferases recognizes specific protein sequences, resulting in the linkage of a variety of oligosaccharides to proteins.
(d) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER.

Answer: 

Cells have oligosaccharides displayed on their cell surface that are important for cell-cell recognition. Your friend discovered a transmembrane glycoprotein, GP1, on a pathogenic yeast cell that is recognized by human immune cells. He decides to purify large amounts of GP1 by expressing it in bacteria. To his purified protein he then adds a branched 14-sugar oligosaccharide to the asparagine of the only Asn-X-Ser sequence found on GP1 (Figure Q15-48). Unfortunately, immune cells do not seem to recognize this synthesized glycoprotein. Which of the following statements is a likely explanation for this problem?

Cells have oligosaccharides displayed on their cell surface that are important for cell-cell recognition. Your friend discovered a transmembrane glycoprotein, GP1, on a pathogenic yeast cell that is recognized by human immune cells. He decides to purify large amounts of GP1 by expressing it in bacteria. To his purified protein he then adds a branched 14-sugar oligosaccharide to the asparagine of the only Asn-X-Ser sequence found on GP1 (Figure Q15-48). Unfortunately, immune cells do not seem to recognize this synthesized glycoprotein. Which of the following statements is a likely explanation for this problem?

(a) The oligosaccharide should have been added to the serine instead of the asparagine.
(b) The oligosaccharide should have been added one sugar at a time.
(c) The oligosaccharide needs to be further modified before it is mature.
(d) The oligosaccharide needs a disulfide bond.

Answer: 

Which of the following statements about disulfide bond formation is false?

Which of the following statements about disulfide bond formation is false?

(a) Disulfide bonds do not form under reducing environments.
(b) Disulfide bonding occurs by the oxidation of pairs of cysteine side chains on the protein.
(c) Disulfide bonding stabilizes the structure of proteins.
(d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing.

Answer: 

N-linked oligosaccharides on secreted glycoproteins are attached to

N-linked oligosaccharides on secreted glycoproteins are attached to 

(a) nitrogen atoms in the polypeptide backbone.
(b) the serine or threonine in the sequence Asn-X-Ser/Thr.
(c) the N-terminus of the protein.
(d) the asparagine in the sequence Asn-X-Ser/Thr.

Answer: 

Which of the following statements about vesicular membrane fusion is false?

Which of the following statements about vesicular membrane fusion is false?

(a) Membrane fusion does not always immediately follow vesicle docking.
(b) The hydrophilic surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur.
(c) The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion.
(d) The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane and the target organelle membrane together so that their lipids can intermix.

Answer: 

An individual transport vesicle

An individual transport vesicle 

(a) contains only one type of protein in its lumen.
(b) will fuse with only one type of membrane.
(c) is endocytic if it is traveling toward the plasma membrane.
(d) is enclosed by a membrane with the same lipid and protein composition as the membrane of the donor organelle.

Answer: 

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?

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?

(a) clathrin
(b) Rab
(c) dynamin
(d) adaptin

Answer: 

Which of the following protein families are not involved in directing transport vesicles to the target membrane?

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

Answer: 

Molecules to be packaged into vesicles for transport are selected by

Molecules to be packaged into vesicles for transport are selected by 

(a) clathrin.
(b) adaptins.
(c) dynamin.
(d) SNAREs.

Answer: 

Which of the following statements about vesicle budding from the Golgi is false?

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.

Answer: 

Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels?

Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels?

(a) lysosome í endosome í plasma membrane
(b) ER í lysosome í plasma membrane
(c) Golgi í lysosome í plasma membrane
(d) ER í Golgi í plasma membrane

Answer: 

Which of the following statements is true?

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.

Answer: 

Which of the following statements about a protein in the lumen of the ER is false?

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.

Answer: 

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?

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.

Answer: 

In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?

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

Answer: 

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?

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 the above


Answer: 

Most proteins destined to enter the endoplasmic reticulum _________.

Most proteins destined to enter the endoplasmic reticulum _________.

(a) are transported across the membrane after their synthesis is complete.
(b) are synthesized on free ribosomes in the cytosol.
(c) begin to cross the membrane while still being synthesized.
(d) remain within the endoplasmic reticulum.

Answer: