cell bio test 3 multiple choice

The following happens when a G-protein-coupled receptor activates a G protein. Question options: a) The α subunit exchanges its bound GDP for GTP. b) It activates the α subunit and inactivates the βγ complex. c) The β subunit exchanges its bound GDP for GTP. d) The GDP bound to the α subunit is phosphorylated to form bound GTP.

a) The α subunit exchanges its bound GDP for GTP.

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 Question options: a) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP b) a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO c) a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO d) a muscle cell that has cyclic GMP phosphodiesterase constitutively active

a) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP

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? Question options: a) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras. b) The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly. c) The cells you create will run out of the GTP necessary to activate Ras. d) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras.

d) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras.

The hydrolysis of GTP to GDP carried out by tubulin molecules ________________. Question options: a) occurs because the pool of free GDP has run out. b) tips the balance in favor of microtubule assembly. c) provides the energy needed for tubulin to polymerize. d) allows the behavior of microtubules called dynamic instability.

d) allows the behavior of microtubules called dynamic instability.

Figure Q17-40A shows how the movement of dynein causes the flagellum to bend. If instead of the normal situation, the polarity of the adjacent doublet of microtubules were to be reversed (see Figure Q17-40B), what do you predict would happen? Figure Q17-40 Question options: a) Bending would occur exactly as diagrammed in Figure Q17-40A. b) Bending would occur, except that the right microtubule doublet would move down relative to the left one. c) No bending would occur. d) The two microtubule doublets would slide away from each other.

b) Bending would occur, except that the right microtubule doublet would move down relative to the left one.

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

b) a protein that stimulates hydrolysis of GTP by the Ras protein

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? Figure Q16-63 Question options: a) addition of a drug that increases the affinity of protein Y and Ras b) addition of a drug that blocks protein Y from interacting with its target c) addition of a drug that prevents protein X from activating Ras d) addition of a drug that increases the activity of protein Y

b) addition of a drug that blocks protein Y from interacting with its target

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________. Question options: a) to create DAG. b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane. c) activate the RTK. d) directly phosphorylate akt.

b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.

All members of the steroid hormone receptor family __________________. Question options: a) do not undergo conformational changes. b) interact with signal molecules that diffuse through the plasma membrane. c) are cell-surface receptors. d) are found only in the cytoplasm.

b) interact with signal molecules that diffuse through the plasma membrane.

Which of the following items is not important for flagellar movement? Question options: a) microtubules b) sarcoplasmic reticulum c)ATP d) dynein

b) sarcoplasmic reticulum

The length of time a G protein will signal is determined by _______. Question options: a) the degradation of the G protein after Gα separates from Gβγ b) the GTPase activity of Gα c) the activity of phosphatases that turn off G proteins by dephosphorylating Gα. d) the activity of phosphatases that turn GTP into GDP.

b) the GTPase activity of Gα

Which of the following mechanisms is not directly involved in inactivating an activated RTK? Question options: a) removal of the RTK from the plasma membrane by endocytosis b) dephosphorylation by protein tyrosine phosphatases c) digestion of the RTK in lysosomes d) dephosphorylation by serine/threonine phosphatases

d) dephosphorylation by serine/threonine phosphatases

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________. Question options: a) activating a receptor tyrosine kinase. b) activating an intracellular protein kinase. c) activating a G protein. d) diffusing into cells and stimulating the cyclase directly.

d) diffusing into cells and stimulating the cyclase directly.

Question 10 1 / 1 point A protein kinase can act as an integrating device in signaling if it ___________________. Question options: a) phosphorylates more than one substrate. b) initiates a phosphorylation cascade involving two or more protein kinases. c) catalyzes its own phosphorylation. d) is activated by two or more proteins in different signaling pathways.

d) is activated by two or more proteins in different signaling pathways.

From the information in Figure Q16-61, which of the following statements is incorrect? Question options: a) The GPCR and the RTK both activate phospholipase C. b) Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators. c) Ras is activated only when the RTK is active and not when the GPCR is active. d) CaM-kinase is only activated when the GPCR is active and not when the RTK is active.

d) CaM-kinase is only activated when the GPCR is active and not when the RTK is active.

Which of the following statements is true? Question options: a) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. b) 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. c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. d) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

d) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Which of the following statements about the function of the centrosome is false? Question options: a) Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules. b) Centrosomes are the major microtubule-organizing center in animal cells. c) Centrosomes contain hundreds of copies of the g-tubulin ring complex important for microtubule nucleation. d) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

d) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

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

d) PI 3-kinase phosphorylates a lipid in the plasma membrane.

Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-10 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose a-helical region is twice as long as that of a normal intermediate filament by duplicating the normal a-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFad. If you were to assemble intermediate filaments using IFad as the subunit, which of the following predictions describes the most likely outcome? Figure Q17-10 Question options: a) Filaments assembled using IF ad will form dimers that are twice as long as dimers assembled from normal intermediate filaments. b) Sixteen tetramers assembled from IF ad will be needed for a rope like structure to form. c)Filaments assembled using IF ad will interact with different cytoskeletal components. d) Dimers of IF ad will form by interactions with the N-terminal globular head and the C-terminal globular tail. View Feedback

a) Filaments assembled using IF ad will form dimers that are twice as long as dimers assembled from normal intermediate filaments.

Which of the following statements about microtubules is true? Question options: a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. b) The centromere nucleates the microtubules of the mitotic spindle. c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.

a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.

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

a) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.

Which of the following statements is correct? Kinesins and dyneins ____________________. Question options: a) often move in opposite directions to each other. b) have tails that bind to the filaments. c) derive their energy from GTP hydrolysis. d) move along both microtubules and actin filament

a) often move in opposite directions to each other.

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

a) the expression of a constitutively active phospholipase C

Which of the following statements about the cytoskeleton is false? Question options: a) The cytoskeleton is made up of three types of protein filaments. b) The cytoskeleton controls the location of organelles in eukaryotic cells. c) Covalent bonds between protein monomers hold together cytoskeletal filaments. d) The cytoskeleton of a cell can change in response to the environment

c) Covalent bonds between protein monomers hold together cytoskeletal filaments.

You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________________. Question options: a) MtA is important for the interaction of microtubules with the centrosome. b) MtA will not bind to purified microtubules in a test tube. c) MtA binds to GTP-bound tubulin on microtubules. d) MtA is involved in stabilizing microtubules.

c) MtA binds to GTP-bound tubulin on microtubules

Which of the following statements about molecular switches is false? Question options: a) A GTP-binding protein exchanges its bound GDP for GTP to become activated. b) Serine/threonine kinases are the most common types of protein kinase. c) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. d) Protein kinases transfer the terminal phosphate from ATP onto a protein.

c) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.

Which of the following statements about molecular switches is false? Question options: a) Protein kinases transfer the terminal phosphate from ATP onto a protein. b) Serine/threonine kinases are the most common types of protein kinase. c) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.

c) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.

Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure Q17-33. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be false? Figure Q17-33 Question options: a) The black cargo moving toward the axon terminal contains a domain that specifically interacts with the tail domain of a particular kind of motor. b) The gray cargo is attached to dynein. c) The black cargo and the gray cargo are moving along microtubules of opposite polarity. d) The black cargo and the gray cargo require ATP hydrolysis for their motion.

c) The black cargo and the gray cargo are moving along microtubules of opposite polarity.

Which of the following statements about G-protein-coupled receptors (GPCRs) is false? Question options: a) GPCRs are used in endocrine, paracrine, and neuronal signaling. b) GPCRs are the largest family of cell-surface receptors in humans. c) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains. d) GPCRs are found in yeast, mice, and humans.

c) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

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 gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein c) a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive d) 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

Which of the following statements about the structure of microtubules is false? Question options: a) The two ends of a protofilament are chemically distinct, with a-tubulin exposed at one end and b-tubulin exposed at the other end. b) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity. c) a-Tubulin and b-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments. d) Microtubules are built from protofilaments that come together to make a hollow structure.

c) a-Tubulin and b-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

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? Question options: a) addition of a drug that prevents GTP hydrolysis by Gα b) addition of a drug that activates adenylyl cyclase c) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive d) addition of a drug that mimics the ligand of ERC1

c) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive

The graph in Figure Q17-31 shows the time course of the polymerization of pure tubulin in vitro. Assume that the starting concentration of free tubulin is higher than it is in cells. Figure Q17-31 Three parts of the curve are labeled above it as A, B, and C. You conduct a similar in vitro tubulin-polymerization experiment, only you include purified centrosomes in your preparation. When you plot your data, which part of your graph should be most dissimilar to the curve shown in Figure Q17-31? Question options: a)B b) None. The shape of my graph should be identical to the graph produced when tubulin is polymerized in the absence of purified centrosomes. c)A d)C

c)A