Quiz 10

Which type of cell signaling does not rely on the diffusion of a chemical signal molecule? -endocrine -All of these choices are correct. -paracrine -autocrine -contact-dependent

contact-dependent

If two signaling pathways are activated simultaneously: -All of these choices are correct. -they may strengthen each other. -one may inhibit the other. -they may inhibit each other.

All of these choices are correct.

To have communication between cells, you must have a: -signaling molecule. -All of these choices are correct. -receptor. -responding cell.

All of these choices are correct.

How are steroid hormone receptors and cell-surface receptors similar? -When bound to their ligand, both types enter the nucleus to activate transcription. -Both types undergo a conformational change when they bind to their ligand. -Both types cause G proteins to exchange GDP for GTP. -When activated, both types carry signals across the plasma membrane.

Both types undergo a conformational change when they bind to their ligand.

What would happen to the signaling cascade if phosphatases were nonfunctional? -None of the other answer options is correct. -It would slow down in the absence of ligand. -It would stop in the absence of ligand. -It would continue in the absence of ligand.

It would continue in the absence of ligand.

When a ligand binds to a G protein-coupled receptor, which of the following would you expect to happen FIRST? -The amount of cAMP in the cytoplasm increases. -None of the other answer options is correct. -Phosphodiesterase activity increases. -Adenylyl cyclase activity increases. -Protein kinase activity increases.

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? -The G protein-coupled receptor might carry a mutation, so that it fails to undergo a conformational change upon the binding of its ligand. -All of these choices are correct. -The G protein-coupled receptor might carry a mutation that affects the receptor's transmembrane portion. -These cells might carry mutations in the downstream signaling pathway associated with this G protein-coupled receptor.

All of these choices are correct.

Defects in cell signaling can lead to a cancerous cell as a result of: -overproduction of a receptor that triggers cell division. -a defective signal transduction protein that stays in the activated state and triggers cell division continuously. -overproduction of signals that trigger cell division. -a defective receptor that stays in the activated state and triggers cell division continuously. -All of these choices are correct.

All of these choices are correct.

According to Figure 9.6, what is a key difference between cell signaling by a cell-surface receptor and cell signaling by an intracellular receptor? -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. -Cell-surface receptors bind to specific signaling molecules; intracellular receptors bind any signaling molecule. -Cell-surface receptors typically bind to signaling molecules that are smaller than those bound by intracellular receptors. -None of the other answer options is correct. -Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.

Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.

A given cell usually only has one signaling pathway. -False -True

False

What does a ligand-gated channel do? -It activates a G protein. -It triggers the activity of a phosphatase. -It binds small, nonpolar signaling molecules. -It allows ions to move across the plasma membrane.

It allows ions to move across the plasma membrane.

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? -It prevents the signaling cell from producing the signal. -It prevents the receptor from binding to the signal. -It prevents the termination of the signal. -It prevents the receptor from becoming activated.

It prevents the receptor from becoming activated.

Review the experiments by Kohler and Lipton described in Figure 9.5. What is the key difference between blood serum and blood plasma that affects their ability to help fibroblasts grow in culture? -Plasma contains more platelet cells than serum, and platelet cells inhibit cell growth. -Molecules found in serum promote cell growth; these molecules are not found in plasma. -Serum contains more platelet cells than plasma, and platelet cells promote cell growth. -Molecules found in plasma inhibit cell growth; these molecules are not found in serum.

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? -Steroid hormone receptors and receptor kinases -Ligand-gated ion channels and receptor kinases -Steroid hormone receptors and ligand-gated ion channels

Steroid hormone receptors and receptor kinases

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? -The G protein would be active and signaling, despite the lack of ligand. -The signal wouldn't be affected; the ligand would be unable to bind due to the conformational change. -The G protein would be active but unable to signal due to the lack of ligand. -The signal wouldn't be affected; there is no ligand, thus no signal.

The G protein would be active and signaling, despite the lack of ligand.

What causes the inactivation of a G protein? -A phosphatase removes the inorganic phosphate group from GTP. -The beta and gamma subunits trigger the hydrolysis of GTP to GDP. -The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate. -The inactive receptor catalyzes the replacement of GTP by GDP.

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? -The cascade serves to amplify the signal, so one activated receptor can have a significant response. -Having a cascade allows the cell to respond to different signals. -The cascade makes signaling easier to shut off or terminate. -Having several intermediates allows for greater control of the response.

The cascade serves to amplify the signal, so one activated receptor can have a significant response.

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? -The signaling molecule is nonpolar and binds a cell-surface receptor. -The signaling molecule is polar and can diffuse into the cell. -The signaling molecule doesn't need a receptor. -The receptor is in the interior of the cell.

The receptor is in the interior of the cell.

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? -The response of the cell would last longer than it normally would. -The signal would still bind the receptor, so there would be no effect. -The response of the cell would be shorter than it normally would.

The response of the cell would last longer than it normally would.

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? -There would be no change in the rate of DNA uptake. -There would be a smaller than normal increase in the rate of DNA uptake. -There would be a decrease in the rate of DNA uptake. -There would be a larger than normal increase in the rate of DNA uptake.

There would be no change in the rate of DNA uptake.

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? -These chemical inhibitors likely enter eukaryotic cells and interfere with components of the signal transduction pathway. -These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding. -These chemical inhibitors likely interfere with the termination of signaling, so eukaryotic cells can't process new signals. -These chemical inhibitors likely enter the nucleus and prevent the transcription of the pathway of interest's target genes.

These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding.

Signaling pathways have been conserved in a wide range of organisms. -False -True

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 continuously activated receptor in the absence of ligand -a Ras molecule that has no GTPase activity -a continuously inactive MAP kinase pathway and an inactive Ras protein -a continuously active receptor and an inactive Map kinase pathway -a continuously active Ras protein and an inactive MAP kinase pathway

a Ras molecule that has no GTPase activity

The activation of protein kinase A by cyclic AMP binding likely occurs because of: -the binding of GTP to protein kinase A. -a conformational change to protein kinase A. -the phosphorylation of protein kinase A. -the activity of a phosphatase.

a conformational change to protein kinase A.

A drug designed to inhibit the response of cells to the steroid testosterone would almost certainly result in which of the following? -lower levels of cAMP -a decrease in G protein activity -a decrease in the transcription of certain genes -a decrease in receptor kinase activity -an increase in cytosolic calcium levels

a decrease in the transcription of certain genes

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 mutation that prevents the binding of the normal extracellular signal to the receptor -a mutation that prevents dimerization of the receptor -a mutation that destroys the kinase activity of the receptor -a mutation that inactivates the phosphatase that dephosphorylates the activated receptor

a mutation that inactivates the phosphatase that dephosphorylates the activated receptor

Which of the following would NOT be considered a cell-surface receptor? -a receptor that must form a dimer after binding the ligand to transmit a signal -a receptor that causes GDP to be exchanged for GTP in a G protein -a receptor that allows ions to enter the cell when a ligand binds -a receptor that binds a nonpolar steroid hormone and activates transcription

a receptor that binds a nonpolar steroid hormone and activates transcription

Signal amplification relies on: -a sequential increase in the different components of the signal transduction pathway. -increasing amounts of ligand as signal transduction proceeds. -increased activity of protein phosphatases. -increasing numbers of cell-surface receptors as the signal is transduced.

a sequential increase in the different components of the signal transduction pathway.

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 signaling cell -a receptor protein -a signaling molecule -None of the other answer options is correct. -a responding cell

a signaling molecule

In the context of cell signaling, to what does the term ligand refer? -a signaling molecule -the extracellular domain of a receptor protein -a type of gated channel -the proteins activated as part of a signal transduction pathway

a signaling molecule

The presence of excess EGF receptors can result in: -excessive cell division. -normal cell division. -diminished cell division.

excessive cell division

Ras is a type of G protein because it: -is only active when it binds GTP. -responds to the activation of G protein-coupled receptors. -triggers the formation of cyclic AMP. -All of these choices are correct.

is only active when it binds GTP

Which type of protein adds a phosphate group to another molecule? -kinase -phosphatase -G protein -phosphorylase

kinase

Which of the following terminates a cell-signaling event that is initiated by a G protein-coupled receptor? -phosphatase activity -protein kinase activity -adenylyl cyclase activity -None of the other answer options is correct.

phosphatase activity

Cyclic AMP (cAMP) is an example of a(n): -effector or target protein. -second messenger. -ligand. -G protein.

second messenger

Figure 9.15 shows how normal signaling works with a Ras protein acting downstream of a receptor kinase. 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? -the addition of a drug that prevents the dimerization of the receptor kinase -the addition of a drug that prevents the phosphorylation of the receptor kinase -the addition of a drug that increases the binding affinity of Ras for MAP kinase enzymes in the cytoplasm -the addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus

the addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus

GTP binding occurs on which subunit of a G protein? -the alpha subunit -the gamma subunit -GTP binds both beta and gamma subunits. -the beta subunit

the alpha unit

In the G protein-coupled signal transduction pathway, phosphatases are responsible for the inactivation of: -protein kinase A. -the protein target activated by protein kinase A. -All of these choices are correct. -adenylyl cyclase. -the alpha subunit of a G protein.

the protein target activated by protein kinase A.

Why do the functions of many receptor kinases depend on the fluid nature of the plasma membrane? -The generation of cAMP requires a fluid membrane. -Binding of ligand to the receptor requires a fluid membrane. -The receptor monomers must move together and dimerize to be activated. -Phosphorylation requires a fluid membrane.

the receptor monomers must move together and dimerize to be activated

Ion channels can be involved in cell signaling because: -they interact with G proteins. -Ion channels are not involved in cell signaling. -their signal is amplified in the cell by a series of phosphorylation events. -they lead to receptor phosphorylation. -they receive signals from other cells and lead to a cellular response.

they receive signals from other cells and lead to a cellular response.

How does an "activated" receptor transfer information into the cell? -by decreased phosphorylation of the receptor -by altering the ligand-binding site of the receptor -by increased translation of the receptor -through a conformational change of the receptor

through a conformational change of the receptor

What is the function of adenylyl cyclase? -to form protein kinase A -to form cyclic AMP -to phosphorylate cyclic AMP -to phosphorylate protein kinase A

to form cyclic AMP