Bio 150 Launchpad 10 & 11
To have communication between cells, you must have a: a. signaling molecule. b. receptor. c. responding cell. d. All of these choices are correct.
d. All of these choices are correct.
The property of dynamic instability implies that the individual protein subunits of microtubules are held together by: a. All of these choices are correct. b. disulfide bonds. c. noncovalent interactions. d. covalent bonds.
c. noncovalent interactions.
What is the function of adenylyl cyclase? a. to phosphorylate cyclic AMP b. to phosphorylate protein kinaseA c. to form protein kinase A d. to form cyclic AMP
c. to form protein kinase A
Cancer can be characterized by: a. All of these choices are correct. b. metastasized tumor cells that leave the tumor and invade distant parts of the body. c. a mass of rapidly dividing cells called a tumor. d. cells with an enhanced ability to adhere to proteins in the basal lamina.
a. All of these choices are correct.
Microtubules increase in length: a. All of these choices are correct. b. if free tubulin dimers are available. c. more quickly at one end than the other. d. by growing outward from the centrosome. e. in cycles, following rapid depolymerization.
a. All of these choices are correct.
What is the advantage of forcing materials to travel through cells instead of between cells? a. All of these choices are correct. b. Cells can control which materials are transported. c. Exposure to toxins is limited. d. Exposure to bacteria or viruses is limited.
a. All of these choices are correct.
Why are the ends of microfilaments and microtubules called "plus ends" and "minus ends"? a. Because monomers are added more quickly to one end (the "plus end") than they are to the other end (the "minus end"). b. Because polymerization occurs at one end (the "plus end") and depolymerization occurs at the other end (the "minus end"). c. Because monomers can be added to one end only (the "plus end"), and can only be removed from the other end (the "minus end"). d. Because the actin and tubulin monomers that make up microfilaments and microtubules have evolved more rapidly than most other proteins.
a. Because monomers are added more quickly to one end (the "plus end") than they are to the other end (the "minus end").
How are steroid hormone receptors and cell-surface receptors similar? a. Both types undergo a conformational change when they bind to their ligand. b. When bound to their ligand, both types enter the nucleus to activate transcription. c. When activated, both types carry signals across the plasma membrane. d. Both types cause G proteins to exchange GDP for GTP.
a. Both types undergo a conformational change when they bind to their ligand.
A given cell usually only has one signaling pathway. a. False b. True
a. False
What would happen to the signaling cascade if phosphatases were nonfunctional? a. It would continue in the absence of ligand. b. It would stop in the absence of ligand. c. It would slow down in the absence of ligand. d. None of the other answer options is correct.
a. It would continue in the absence of ligand.
What is the key difference between blood serum and blood plasma that affects their ability to help fibroblasts grow in culture? a. Molecules found in serum promote cell growth; these molecules are not found in plasma. b. Plasma contains more platelet cells than serum, and platelet cells inhibit cell growth. c. Molecules found in plasma inhibit cell growth; these molecules are not found in serum. d. Serum contains more platelet cells than plasma, and platelet cells promote cell growth.
a. Molecules found in serum promote cell growth; these molecules are not found in plasma.
Which of the following are most directly involved in changes in gene expression? a. Steroid hormone receptors and receptor kinases b. Ligand-gated ion channels and receptor kinases c. Steroid hormone receptors and ligand-gated ion channels
a. Steroid hormone receptors and receptor kinases
What causes the inactivation of a G protein? a. The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate. b. A phosphatase removes the inorganic phosphate group from GTP. c. The beta and gamma subunits trigger the hydrolysis of GTP to GDP. d. The inactive receptor catalyzes the replacement of GTP by GDP.
a. The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate.
During the signal transduction process, the signal often triggers a signal transduction cascade. For example, an activated receptor activates hundreds of protein A. Each activated protein A activates hundreds of protein B and so on until a cellular response occurs. What purpose does this cascade serve? a. The cascade serves to amplify the signal, so one activated receptor can have a significant response. b. Having several intermediates allows for greater control of the response. c. The cascade makes signaling easier to shut off or terminate. d. Having a cascade allows the cell to respond to different signals.
a. The cascade serves to amplify the signal, so one activated receptor can have a significant response.
What would happen in a cell if its α-tubulin was mutated and unable to bind to its β tubulin? a. The cell would have no microtubules. b. The cell would have no intermediate filaments. c. The cell would be unaffected. d. The cell would have no microfilaments.
a. The cell would have no microtubules.
Why do the functions of many receptor kinases depend on the fluid nature of the plasma membrane? a. The receptor monomers must move together and dimerize to be activated. b. Phosphorylation requires a fluid membrane. c. The generation of cAMP requires a fluid membrane. d. Binding of ligand to the receptor requires a fluid membrane.
a. The receptor monomers must move together and dimerize to be activated.
Recall from the text the example of cell communication in Streptococcus pneumoniae: The rate of DNA uptake by pneumococcal cells increases sharply when they are at high density, due to changes in gene expression brought about by signaling between cells. If the pneumococcal cells did not express receptor proteins, how would the rate of DNA uptake be affected when the cells reach high density? a. There would be no change in the rate of DNA uptake. b. There would be a decrease in the rate of DNA uptake. c. There would be a larger than normal increase in the rate of DNA uptake. d. There would be a smaller than normal increase in the rate of DNA uptake.
a. There would be no change in the rate of DNA uptake.
Signaling pathways have been conserved in a wide range of organisms. a. True b. False
a. True
A number of mutations have been described in G proteins, such as Ras, that have profound effects on their activity. For example, some mutations greatly increase the affinity of the G protein for GDP, making it very difficult for GDP to be exchanged for GTP. Other mutations prevent the hydrolysis of GTP to GDP. Which of the following scenarios would still result in a proliferation signal via the kinase cascade in the absence of ligand binding to its receptor kinase? a. a Ras molecule that has no GTPase activity b. a continuously inactive MAP kinase pathway and an inactive Ras protein c. a continuously activated receptor in the absence of ligand d. a continuously active receptor and an inactive Map kinase pathway e. a continuously active Ras protein and an inactive MAP kinase pathway
a. a Ras molecule that has no GTPase activity
A drug designed to inhibit the response of cells to the steroid testosterone would almost certainly result in which of the following? a. a decrease in the transcription of certain genes b. an increase in cytosolic calcium levels c. a decrease in receptor kinase activity d. lower levels of cAMP e. a decrease in G protein activity
a. a decrease in the transcription of certain genes
Which of the following is associated with microfilaments? a. adherens junction b. desmosomes c. cilia and flagella
a. adherens junction
Kinesin motor proteins use ATP to: a. carry vesicles along a microtubule within a cell in a minus-to-plus direction. b. carry vesicles along a microfilament within a cell in a plus-to-minus direction. c. slide along microfilaments to contract muscle cells. d. carry vesicles along a microfilament within a cell in a minus-to-plus direction. e. carry vesicles along a microtubule within a cell in a plus-to-minus direction.
a. carry vesicles along a microtubule within a cell in a minus-to-plus direction.
Which of the following is associated with intermediate filaments? a. desmosomes b. adherens junction c. cilia and flagella
a. desmosomes
Which motor protein(s) would you find in a flagellum? a. dynein b. kinesin c. myosin d. both myosin and dynein
a. dynein
Which type of protein adds a phosphate group to another molecule? a. kinase b. phosphorylase c. phosphatase d. G protein
a. kinase
Zebrafish embryos change the color of the melanophore cells in their skin to a darker shade by: a. kinesin motor proteins moving pigment granules outward from the center of the cell. b. dynein motor proteins moving pigment granules outward from the center of the cell. c. kinesin motor proteins moving pigment granules inward toward the center of the cell. d. dynein motor proteins moving pigment granules inward toward the plus end of microtubules. e. dynein motor proteins moving pigment granules inward toward the center of the cell.
a. kinesin motor proteins moving pigment granules outward from the center of the cell.
Microtubules and microfilaments are said to be "dynamic" elements of the cytoskeleton. In this case, "dynamic" means that: a. microtubules and microfilaments are assembled and disassembled and then reassembled again in a regulated manner. b. they are constantly changing and are never in the same place for very long. c. once individual microfilaments and microtubules have formed, they can change shape and move around inside the cell.
a. microtubules and microfilaments are assembled and disassembled and then reassembled again in a regulated manner.
Kinesin is a motor protein found attached to: a. microtubules. b. intermediate filaments. c. microfilaments. d. tubulin.
a. microtubules.
Microfilaments increase in length: a. more quickly at one end than the other. b. if free tubulin dimers are available. c. in cycles, following rapid depolymerization. d. All of these choices are correct. e. by assembling outward from the centrosome.
a. more quickly at one end than the other.
The internal cytoskeletal structure of cilia and flagella grows out from a structure called a basal body located near the cell surface. Based on this information, where would you predict the plus end of the microtubules to be located? a. near the tip of the cilia or flagella b. at both ends of the cilia or flagella c. It is not possible to predict from the information provided. d. near the basal body
a. near the tip of the cilia or flagella
In nerve cells, the centrosome is located near the nucleus. Vesicles move from near the nucleus to the end of long extensions (axons) along microtubules. Based on these two facts, it is possible to conclude that these vesicles are moving in the _____ direction on the microtubule using the motor protein _____. a. plus end; kinesin b. plus end; dynein c. minus end; kinesin d. minus end; dynein
a. plus end; kinesin
If two signaling pathways are activated simultaneously: a. one may inhibit the other. b. All of these choices are correct. c. they may inhibit each other. d. they may strengthen each other.
b. All of these choices are correct.
What is a key difference between cell signaling by a cell-surface receptor and cell signaling by an intracellular receptor? a. Cell-surface receptors typically bind to signaling molecules that are smaller than those bound by intracellular receptors. b. Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules. c. Signaling molecules that bind to cell-surface receptors lead to cellular responses restricted to the cytoplasm; signaling molecules that bind to intracellular receptors lead to cellular responses restricted to the nucleus. d. None of the other answer options is correct. e. Cell-surface receptors bind to specific signaling molecules; intracellular receptors bind any signaling molecule.
b. Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.
What does a ligand-gated channel do? a. It allows ions to move across the plasma membrane. b. It activates a G protein. c. It triggers the activity of a phosphatase. d. It binds small, nonpolar signaling molecules.
b. It activates a G protein.
Which one of the following statements about intracellular transport is TRUE? a. Intermediate filaments and microfilaments facilitate cellular movement, but microtubules do not. b. Microtubules and microfilaments facilitate cellular movement, but intermediate filaments do not. c. Microtubules and intermediate filaments facilitate cellular movement, but microfilaments do not. d. Intermediate filaments, microfilaments, and microtubules all facilitate cellular movement of one kind or another.
b. Microtubules and microfilaments facilitate cellular movement, but intermediate filaments do not.
The extracellular matrix is composed of: (1) proteins; (2) polysaccharides; (3) nucleic acids. a. All of these statements are correct. b. Statements (1) and (2) are correct. c. Statement (3) is correct. d. Statement (1) is correct. e. Statement (2) is correct.
b. Statements (1) and (2) are correct.
How would the signal of a G protein-coupled receptor, without ligand, be affected if you made a G protein that converted GDP to GTP on its own without needing to be activated by the G protein-coupled receptor? a. The signal wouldn't be affected; there is no ligand, thus no signal. b. The G protein would be active and signaling, despite the lack of ligand. c. The signal wouldn't be affected; the ligand would be unable to bind due to the conformational change. d. The G protein would be active but unable to signal due to the lack of ligand.
b. The G protein would be active and signaling, despite the lack of ligand.
Phosphatases are a family of enzymes that remove phosphate groups from specific proteins; these phosphate groups had been added to the proteins by protein kinases. Vanadate is an inhibitor of phosphatases in eukaryotic cells. What effect would vanadate have on the response of cells to signals received by receptor kinases? a. The response of the cell would be shorter than it normally would. b. The response of the cell would last longer than it normally would. c. The signal would still bind the receptor, so there would be no effect.
b. The response of the cell would last longer than it normally would.
You are studying a newly discovered growth factor. You find that this growth factor stimulates the proliferation of chicken cells grown in the laboratory. You have also found that the receptor that binds the growth factor is a receptor kinase. Which of the following mutations would you expect to promote uncontrolled cell proliferation? a. a mutation that prevents the binding of the normal extracellular signal to the receptor b. a mutation that inactivates the phosphatase that dephosphorylates the activated receptor c. a mutation that destroys the kinase activity of the receptor d. a mutation that prevents dimerization of the receptor
b. a mutation that inactivates the phosphatase that dephosphorylates the activated receptor
Which of the following would NOT be considered a cell-surface receptor? a. a receptor that causes GDP to be exchanged for GTP in a G protein b. a receptor that binds a nonpolar steroid hormone and activates transcription c. a receptor that allows ions to enter the cell when a ligand binds d. a receptor that must form a dimer after binding the ligand to transmit a signal
b. a receptor that binds a nonpolar steroid hormone and activates transcription
Cilia and flagella: a. are specialized organelles that move by rotary motion. b. are specialized organelles that propel some algae, plant, and animal cells. c. are specialized cells that move by rotary motion. d. contain microfilaments arranged in nine pairs around the periphery and two microfilaments in the center. e. contain microtubules arranged in nine pairs around the periphery and two microfilaments in the center.
b. are specialized organelles that propel some algae, plant, and animal cells.
Which of the following cytoskeletal elements is capable of assembling and disassembling in the cell? a. intermediate filaments b. both microtubules and microfilaments c. microfilaments d. microtubules
b. both microtubules and microfilaments
Which of the following is associated with microtubules? a. adherens junction b. cilia and flagella c. desmosomes
b. cilia and flagella
Which type of cell signaling does not rely on the diffusion of a chemical signal molecule? a. endocrine b. contact-dependent c. All of these choices are correct. d. paracrine e. autocrine
b. contact-dependent
The presence of excess EGF receptors can result in: a. diminished cell division. b. excessive cell division. c. normal cell division.
b. excessive cell division.
Dynein is a motor protein found attached to: a. lamin. b. microtubules. c. microfilaments. d. intermediate filaments.
b. microtubules.
Cyclic AMP (cAMP) is an example of a(n): a. G protein. b. second messenger. c. ligand. d. effector or target protein.
b. second messenger.
You examine a cell line in which Ras is always activated even in the absence of a signaling molecule. This causes constant activation of the kinases in the MAP kinase pathway. Which of the following conditions would be MOST likely to turn off this abnormally active signaling pathway? a. the addition of a drug that prevents the phosphorylation of the receptor kinase b. the addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus c. the addition of a drug that increases the binding affinity of Ras for MAP kinase enzymes in the cytoplasm d. the addition of a drug that prevents the dimerization of the receptor kinase
b. the addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus
In the G protein-coupled signal transduction pathway, phosphatases are responsible for the inactivation of: a. All of these choices are correct. b. the protein target activated by protein kinase A. c. adenylyl cyclase. d. protein kinase A. e. the alpha subunit of a G protein.
b. the protein target activated by protein kinase A.
How does an "activated" receptor transfer information into the cell? a. by decreased phosphorylation of the receptor b. through a conformational change of the receptor c. by increased translation of the receptor d. by altering the ligand-binding site of the receptor
b. through a conformational change of the receptor
When a ligand binds to a G protein-coupled receptor, which of the following would you expect to happen FIRST? a. None of the other answer options is correct. b. The amount of cAMP in the cytoplasm increases. c. Adenylyl cyclase activity increases. d. Protein kinase activity increases. e. Phosphodiesterase activity increases.
c. Adenylyl cyclase activity increases.
A researcher is studying a G protein-coupled receptor in eukaryotic cells. In one group of cells, he notices that even though a ligand can bind to its G protein-coupled receptor, nothing happens. Why could this happen? a. The G protein-coupled receptor might carry a mutation that affects the receptor's transmembrane portion. b. The G protein-coupled receptor might carry a mutation, so that it fails to undergo a conformational change upon the binding of its ligand. c. All of these choices are correct. d. These cells might carry mutations in the downstream signaling pathway associated with this G protein-coupled receptor.
c. All of these choices are correct.
Defects in cell signaling can lead to a cancerous cell as a result of: a. overproduction of a receptor that triggers cell division. b. a defective signal transduction protein that stays in the activated state and triggers cell division continuously. c. All of these choices are correct. d. overproduction of signals that trigger cell division. e. a defective receptor that stays in the activated state and triggers cell division continuously.
c. All of these choices are correct.
Intermediate filaments: a. play an important role in preventing skin from tearing by shear stress. b. undergo little change in length in comparison to microtubules and microfilaments. c. All of these choices are correct. d. play an important role in maintaining cell shape. e. have a diameter that is larger than a microfilament, but smaller than a microtubule.
c. All of these choices are correct.
You strip off all proteins on the cell surface by using a protease (an enzyme that destroys proteins). Now, when you add a specific signaling molecule, the cell still responds. Why is this? a. The signaling molecule is nonpolar and binds a cell-surface receptor. b. The signaling molecule is polar and can diffuse into the cell. c. The receptor is in the interior of the cell. d. The signaling molecule doesn't need a receptor
c. The receptor is in the interior of the cell.
Signal amplification relies on: a. increasing numbers of cell-surface receptors as the signal is transduced. b. increased activity of protein phosphatases. c. a sequential increase in the different components of the signal transduction pathway. d. increasing amounts of ligand as signal transduction proceeds.
c. a sequential increase in the different components of the signal transduction pathway.
Some cytoskeletal elements are more permanent than others. Which components of the cytoskeleton are dynamic structures? a. intermediate filaments b. microtubules c. both microtubules and microfilaments d. microfilaments e. both microtubules and intermediate filaments
c. both microtubules and microfilaments
Myosin motor proteins use ATP to: a. carry vesicles along a microfilament within a cell in a plus-to-minus direction. b. carry vesicles along a microtubule within a cell in a plus-to-minus direction. c. carry vesicles along a microfilament within a cell in a minus-to-plus direction. d. carry vesicles along a microtubule within a cell in a minus-to-plus direction. e. slide along intermediate filaments to contract muscle cells.
c. carry vesicles along a microfilament within a cell in a minus-to-plus direction.
Cadherin is an example of a(n): a. extracellular matrix protein. b. motor protein. c. cell adhesion molecule. d. intermediate filament protein.
c. cell adhesion molecule.
The extracellular matrix is particularly important for which type of tissue? a. muscle b. epithelial c. connective d. nervous
c. connective
Many mutations in receptor kinases that lead to cancer allow the receptor to dimerize and become activated, even in the absence of signaling molecules. An example is a mutant form of the EGF receptor kinase called Her2/neu. An antibody that prevents dimerization of Her2/neu receptor kinases is being tested for its effectiveness in preventing cancer. At which stage does this drug work? a. It prevents the signaling cell from producing the signal. b. It prevents the termination of the signal. c. It prevents the receptor from binding to the signal. d. It prevents the receptor from becoming activated.
d. It prevents the receptor from becoming activated.
Which of the following statements about intracellular transport is TRUE? a. Kinesin and myosin move substances toward the "minus end" of microtubules and microfilaments, respectively. b. Myosin and kinesin move substances toward the "minus end" of microtubules and microfilaments, respectively. c. Myosin and kinesin move substances toward the "plus end" of microtubules and microfilaments, respectively. d. Kinesin and myosin move substances toward the "plus end" of microtubules and microfilaments, respectively.
d. Kinesin and myosin move substances toward the "plus end" of microtubules and microfilaments, respectively.
Which one of the following statements about intracellular transport is TRUE? a. Kinesin and dynein move substances along microfilaments. b. Myosin and dynein move substances along microfilaments. c. Kinesin and myosin move substances along microtubules. d. Myosin moves substances along microfilaments.
d. Myosin moves substances along microfilaments.
Many scientists use chemical inhibitors to interfere with normal signaling pathways within eukaryotic cells. If such inhibitors are large, nonpolar molecules, what is the likely method of action of these chemical inhibitors? a. These chemical inhibitors likely interfere with the termination of signaling, so eukaryotic cells can't process new signals. b. These chemical inhibitors likely enter the nucleus and prevent the transcription of the pathway of interest's target genes. c. These chemical inhibitors likely enter eukaryotic cells and interfere with components of the signal transduction pathway. d. These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding.
d. These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding.
The activation of protein kinase A by cyclic AMP binding likely occurs because of: a. the activity of a phosphatase. b. the phosphorylation of protein kinase A. c. the binding of GTP to protein kinase A. d. a conformational change to protein kinase A.
d. a conformational change to protein kinase A.
In the context of cell signaling, to what does the term ligand refer? a. the extracellular domain of a receptor protein b. a type of gated channel c. the proteins activated as part of a signal transduction pathway d. a signaling molecule
d. a signaling molecule
Dynein motor proteins use ATP to: a. carry vesicles along a microtubule within a cell in a minus-to-plus direction. b. carry vesicles along a microfilament within a cell in a minus-to-plus direction. c. slide along microfilaments to contract muscle cells. d. carry vesicles along a microtubule within a cell in a plus-to-minus direction. e. carry vesicles along a microfilament within a cell in a plus-to-minus direction.
d. carry vesicles along a microtubule within a cell in a plus-to-minus direction.
Where would you find a cell adhesion molecule? a. in the microvilli b. in a cilium c. near the centrosome d. in a cell junction
d. in a cell junction
Ras is a type of G protein because it: a. responds to the activation of G protein-coupled receptors. b. All of these choices are correct. c. triggers the formation of cyclic AMP. d. is only active when it binds GTP.
d. is only active when it binds GTP.
The cytoskeleton of plant cells includes: a. tubulin, microfilaments, and intermediate filaments. b. actin, microtubules, and intermediate filaments. c. microtubules, microfilaments, and intermediate filaments. d. microtubules and microfilaments. e. actin, microfilaments, and intermediate filaments.
d. microtubules and microfilaments.
Which is the correct order of cytoskeletal filaments in DECREASING filament diameter? a. microtubules → microfilaments → intermediate filaments b. intermediate filaments → microfilaments → microtubules c. microfilaments → microtubules → intermediate filaments d. microtubules → intermediate filaments → microfilaments
d. microtubules → intermediate filaments → microfilaments
Which one of the following is NOT a cellular function associated with microtubules? a. chromosome segregation b. organization of organelles c. movement of cilia and flagella d. muscle contraction
d. muscle contraction
Which of the following terminates a cell-signaling event that is initiated by a G protein-coupled receptor? a. adenylyl cyclase activity b. protein kinase activity c. None of the other answer options is correct. d. phosphatase activity
d. phosphatase activity
GTP binding occurs on which subunit of a G protein? a. the beta subunit b. GTP binds both beta and gamma subunits. c. the gamma subunit d. the alpha subunit
d. the alpha subunit
Epidermolysis bullosa is a set of rare genetic disorders that is caused by: a. an intermediate filament gene that disrupts hemidesmosomes, weakening epidermal cell connections. b. a keratin gene that disrupts microfilaments, weakening epidermal cell connections. c. a microfilament gene that disrupts desmosomes, weakening epidermal cell connections. d. All of these choices are correct. e. a keratin gene that disrupts intermediate filaments, weakening epidermal cell connections
e. a keratin gene that disrupts intermediate filaments, weakening epidermal cell connections
A chemical that binds to a cell and causes its activity to change is an example of which of the following elements of cellular communication? a. a signaling cell b. None of the other answer options is correct. c. a responding cell d. a receptor protein e. a signaling molecule
e. a signaling molecule
Ion channels can be involved in cell signaling because: a. Ion channels are not involved in cell signaling. b. their signal is amplified in the cell by a series of phosphorylation events. c. they lead to receptor phosphorylation. d. they interact with G proteins. e. they receive signals from other cells and lead to a cellular response.
e. they receive signals from other cells and lead to a cellular response.
