Practice Quiz Chapter 16
Cells signal to one another in various ways. Some use extracellular signal molecules that are dissolved gases, such as ___A___, which can diffuse easily into cells. Others use cytokines, which bind to cytokine receptors. Cytokine receptors have no intrinsic enzyme activity but are associated with cytoplasmic tyrosine kinases called ___B___s, which become activated on the binding of cytokine to its receptor and go on to phosphorylate and activate cytoplasmic transcriptional regulators called ___C___s. Some intracellular signaling pathways involve chains of protein kinases that phosphorylate each other, as seen in the ___D___ signaling module. Lipids can also relay signals in the cell, as we observe when phospholipase C cleaves the sugar-phosphate head off a lipid molecule to generate the two small messenger molecules ___E___ (which remains embedded in the plasma membrane) and ___F___ (which diffuses into the cytosol).
A) NO B) JAK C) STAT D) MAP kinase E) diacylglycerol F) IP3
Cells can signal to each other in various ways. A signal that must be relayed to the entire body is most efficiently sent by ___A___ cells, which produce hormones that are carried throughout the body through the bloodstream. On the other hand, ___B___ methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events. During ___C___ signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells. Finally, ___D___ signaling converts electrical impulses into a chemical signal. Cells receive signals through a ___E___, which can be an integral membrane protein or can reside inside the cell.
A) endocrine B) contact-dependent C) paracrine D) neuronal E) receptor
Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely ____A___ concentration of free Ca2+ in the cytosol, compared with its concentration in the ____B___ space and in the ____C___, creating a steep electrochemical gradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as ____D___ which also binds diacylglycerol, and ____E___ ,which activates CaM-kinases.
A) low B) extracellular C) endoplasmic reticulum D) protein kinase c E) calmodulin
An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface ____A___ that control intracellular signaling proteins. These intracellular signaling proteins ultimately change the activity of ____B___ proteins that bring about cell responses. Intracellular signaling proteins can ____C___ the signal received to evoke a strong response from just a few extracellular signal molecules. A cell that receives more than one extracellular signal at the same time can ____D___ this information using intracellular signaling proteins. ____E___ proteins can act as molecular switches, letting a cell know that a signal has been received. Enzymes that phosphorylate proteins, termed ____F___, can also serve as molecular switches; the actions of these enzymes are countered by the activity of ____G___.
A) receptors B) effector C) amplify D) integrate E) GTP-binding F) protein kinases G) protein phosphatses
G-protein-coupled receptors (GPCRs) all have a similar structure with ____A___ transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of ____B___ subunits, becomes activated. ____C___ of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to ____D___, which is exchanged for ____E___ on stimulation. The intrinsic ____F___ activity of the α subunit is important for inactivating the G protein. ____G___ inhibits this activity of the α subunit, thereby keeping the subunit in an active state.
A) seven B) three C) two D) GDP E) GTP F) GTPase G) cholera toxin
An amplification of a signal could occur when an extracellular signaling molecule binds and activates a GPCR? True False
False
An amplification of a signal could occur when cAMP activates protein kinase A. True False
False
You obtain muscle cells that have an α subunit that cannot hydrolyze GTP but can interact properly with the β and γ subunits. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline? Higher Lower
Lower
You obtain muscle cells that lack the cAMP phosphodiesterase. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline? Higher Lower
Lower
From the data presented in Figure B, which, if any, of proteins A, B, C, and D are involved in the stimulation of DNA synthesis by PDGF? Protein A Protein B Protein C Protein D None of the above
Protein A Protein D
From the data presented in Figure B (above), which, if any, of proteins A, B, C, and D inhibit DNA synthesis? Protein A Protein B Protein C Protein D None of the above
Protein B
From the data presented in Figure B (above), which, if any, of proteins A, B, C, and D seem to have no detectable role in DNA synthesis? Protein A Protein B Protein C Protein D None of the above
Protein C
Antibodies are Y-shaped molecules that have two identical binding sites. Suppose that you have obtained an antibody that is specific for the extracellular domain of an RTK. When the antibody binds to the RTK, it brings together two RTK molecules. If cells containing the RTK were exposed to the antibody, would you expect the kinase to be activated, inactivated, or unaffected? a) activated b) inactivated c) unaffected
a) activated
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.
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.
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.
b) PI 3-kinase phosphorylates a lipid in the plasma membrane.
The rod photoreceptors in the eye are extremely sensitive to light. The cells sense light through a signal transduction cascade involving light activation of a GPCR that activates a G protein that activates cyclic GMP phosphodiesterase. You add a drug that inhibits cyclic GMP phosphodiesterase. How do you predict that the addition of the drug would affect the light-sensing ability of the rod cells? a) The drug would increase the light-sensing response b) The drug decrease the light-sensing response
b) The drug decrease the light-sensing response
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 to RGF 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
b) a mutation that prevents RGFR from binding to RGF
Which of the following is likely to occur more rapidly in response to an extracellular signal? a) changes in mRNA levels b) changes in membrane potential
b) changes in membrane potential
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) interact with signal molecules that diffuse through the plasma membrane
Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as shown below. Which of the following statements below 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.
d) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.
Which one 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.
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.
Akt promotes the survival of many cells. It is activated by an intracellular signaling pathway that is triggered by an RTK that activates PI 3-kinase, as shown below. Which of the following statements is false? a) In the presence of a survival signal, Akt localizes to the plasma membrane by binding to PIP3. b) In the absence of survival signal, Bad inhibits the cell death inhibitor protein Bcl2. c) In the presence of survival signal, the cell death inhibitory protein Bcl2 is active. d) In the absence of survival signal, Bad is phosphorylated.
d) In the absence of survival signal, Bad is phosphorylated.
Rank the following types of cell signaling from 1 to 4, with 1 representing the type of signaling in which the signal molecule travels the least distance and 4 the type of signaling in which the signal molecule travels the largest distance. Paracrine signaling Contact dependent signaling Neuronal signaling Endocrine signaling
2, 1, 3, 4
As shown in the figure above, when adrenaline binds to adrenergic receptors on the surface of a muscle cell, it activates a G protein, initiating an intracellular signaling pathway in which the activated α subunit activates adenylyl cyclase, thereby increasing cAMP levels. The cAMP molecules then activate a cAMP-dependent kinase (PKA) that, in turn, activates enzymes that result in the breakdown of muscle glycogen, lowering glycogen levels. You obtain muscle cells that lack adenylyl cyclase. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline? Higher Lower
Higher
You obtain muscle cells that lack the GPCR. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline? Higher Lower
Higher
An amplification of a signal could occur when adenylyl cyclase produces cyclic AMP. True False
True
An amplification of a signal could occur when protein kinase A phosphorylates target proteins. True False
True
An amplification of a signal could occur when the activated GPCRs cause Gα to separate from Gβ and Gγ. True False
True
Can signaling via a steroid hormone receptor lead to amplification of the original signal? Yes No
Yes
Which one 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.
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.
Which one 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.
a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.
The rod photoreceptors in the eye are extremely sensitive to light. The cells sense light through a signal transduction cascade involving light activation of a GPCR that activates a G protein that activates cyclic GMP phosphodiesterase. You add a drug that is a nonhydrolyzable analog of GTP. How do you predict that the addition of the drug would affect the light-sensing ability of the rod cells? a) The drug would increase the light-sensing response b) The drug would decrease the light-sensing response
a) The drug would increase the light-sensing response
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 below. Which of the following would enhance this effect of the acetylcholine? a) addition of a high concentration of a non-hydrolyzable analog of GTP b) addition of a drug that prevents the α 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
a) addition of a high concentration of a non-hydrolyzable analog of GTP
Which of the following is likely to occur more rapidly in response to an extracellular signal? a) changes in cell secretion b) increased cell division
a) changes in cell secretion
Which of the following is likely to occur more rapidly in response to an extracellular signal? a) changes in protein phosphorylation b) changes in proteins being synthesized
a) changes in protein phosphorylation
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
a) dephosphorylation by serine/threonine phosphatases
Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. The figure below 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
a) the expression of a constitutively active phospholipase C
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 below. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which of the following situations will lead to an increase in Brainytranscription? 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 PPKKKRKVto 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 α subunit of the G protein.
c) A mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive.
The figure below shows that intracellular signaling pathways can be highly interconnected. From the information in the above figure, which of the following statements is incorrect? 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) CaM-kinase is only activated when the GPCR is active and not when the RTK is active. d) Ras is activated only when the RTK is active and not when the GPCR is active.
c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active.
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 muscles, 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 GQF.
c) QGF activates different intracellular signaling pathways in heart muscles, fibroblasts, and nerve cells to produce the different responses observed.
The following happens when a cell-surface receptor activates a G protein. a) The β subunit exchanges its bound GDP for GTP. b) The GDP bound to the α subunit is phosphorylated to form bound GTP. c) The α subunit exchanges its bound GDP for GTP. d) It activates the α subunit and inactivates the βγ complex.
c) The α subunit exchanges its bound GDP for GTP.
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
c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
The figure below 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? a) addition of a drug that prevents protein X from activating Ras b) addition of a drug that increases the affinity of protein Y and Ras c) addition of a drug that blocks protein Y from interacting with its target d) addition of a drug that increases the activity of protein Y
c) addition of a drug that blocks protein Y from interacting with its target
Your friend is studying mouse fur color and has isolated the GPCR responsible for determining its color, as well as the extracellular signal that activates the receptor. She finds that, on addition of the signal to pigment cells (cells that produce the pigment determining fur color), cAMP levels rise in the cell. She starts a biotech company, and the company isolates more components of the signaling pathway responsible for fur color. Using transgenic mouse technology, the company genetically engineers mice that are defective in various proteins involved in determining fur color. The company obtains the following results:· Normal mice have beige (very light brown) fur color.· Mice lacking the extracellular signal have white fur.· Mice lacking the GPCR have white fur.· Mice lacking cAMP phosphodiesterase have dark brown fur.Your friend has also made mice that are defective in the α subunit of the G protein in this signaling pathway. The defective α subunit works normally except that, once it binds GTP, it cannot hydrolyze GTP to GDP. What color do you predict that the fur of these mice will be? a) beige (very light brown) b) white c) dark brown
c) dark brown
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
c) diffusing into cells and stimulating the cyclase directly
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
c) is activated by two or more proteins in different signaling pathways
Acetylcholine acts at a GPCR on heart muscle to make the heart beat more slowly. It does so by ultimately opening K+ channels in the plasma membrane (as shown below),which decreases the cell's excitability by making it harder to depolarize the plasma membrane. Which of the following conditions would increase the effect of acetylcholine? a) addition of a drug that stimulates the GTPase activity of the Gα subunit. b) mutations in the K+ channel that keep it closed all the time. c) modification of the Gα subunit by cholera toxin. d) a mutation that decreases the affinity of the βγ complex of the G protein for the K+channel. e) a mutation in the acetylcholine receptor that prevents its localization on the cell surface. f) adding acetylcholinesterase to the external environment of the cell.
c) modification of the Gα subunit by cholera toxin.