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Ch 11 Cell Communication

Terms in this set (48)

Which of the following is a substance that acts at a long distance from the site at which it is secreted?
a. synaptic signal
b. local regulator
c. paracrine signal
d. neurotransmitter
e. hormone
e. hormone
Yeast cells of mating type a are genetically engineered to produce only mating factor α instead of the normal mating factor a. The gene for the mating factor receptor was unaltered. How will these engineered cells behave in terms of mating?
a. They will only mate with normal mating type α cells.
b. They will mate with each other or with normal mating type a cells, but not with normal mating type α cells.
c. They will only mate with normal mating type a cells.
d. They will only mate each other and not with normal mating type a or α cells.
b. They will mate with each other or with normal mating type a cells, but not with normal mating type α cells.
Hormones are chemical substances produced in one organ that are released into the bloodstream and affect the function of a target organ. Which of the following conditions is required for the target organ to respond to a particular hormone?
a. Cells in the target organ must modify their plasma membranes to allow the hormone to enter the cytoplasm.
b. The target organ must have the opposite mating type of the organ that produced the hormone.
c. The target organ must have receptors that recognize and bind the hormone molecule.
d. The target organ must be the same as the organ that produced the hormone.
c. The target organ must have receptors that recognize and bind the hormone molecule.
Which of the following types of signaling is represented in the figure?
a. paracrine
b. hormonal
c. autocrine
d. synaptic
d. synaptic
In the figure, the dots in the space between the two structures represent which of the following?
a. receptor molecules
b. hormones
c. neurotransmitters
d. signal transducers
c. neurotransmitters
To what does the term "ligand" refer in cell biology?
a. a molecule that can occupy a receptor site while not activating the receptor
b. any small molecule that can bind in a specific manner to a larger one
c. the change in shape that occurs when a signaling molecule binds to its receptor
d. the target cell of a signal molecule
e. the bond that forms between a signaling molecule and its receptor
b. any small molecule that can bind in a specific manner to a larger one
Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding to proteins in the cytoplasm, then altering the pattern of gene expression. Which of the following are likely to be the cytoplasmic proteins to which dioxin binds?
a. transcription factors
b. DNA polymerases
c. growth factor receptors
d. nucleosomes
e. enhancers
a. transcription factors
What is the function of tyrosine-kinase receptors?
a. enzymatic hydrolyzing of the signaling molecule shortly after its arrival
b. allowing specific ions to enter the cell after ligand binding
c. binding to nonpolar signaling molecules such as nitric oxide or the steroid hormones
d. enzymatic degrading of GTP to GDP
e. enzymatic phosphorylation of tyrosine in the receptor protein
e. enzymatic phosphorylation of tyrosine in the receptor protein
When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?
a. signal molecule
b. transducer
c. response molecule
d. relay molecule
a. signal molecule
Which of the following statements about a G protein signaling pathway is true?
a. A G protein bound to GTP is in its active state.
b. A G protein bound to GDP is in its active state.
c. Hydrolysis of bound GTP by a G protein activates the G protein.
d. A G protein-coupled receptor bound to GTP is in its active state.
a. A G protein bound to GTP is in its active state.
Scientists have found that extracellular matrix components may induce specific gene expression in embryonic tissues such as the liver and testes. For this to happen, there must be direct communication between the extracellular matrix and the developing cells. Which kind of transmembrane protein would most likely be involved in this kind of induction?
a. integrins
b. fibronectins
c. actin microfilaments
d. receptor tyrosine kinases
a. integrins
One of the major categories of receptors in the plasma membrane functions by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?
a. ligand-gated ion channels
b. G protein-coupled receptors
c. receptor tyrosine kinases
d. steroid receptors
c. receptor tyrosine kinases
Which of the following statements describes a likely effect of a drug designed that inhibits the cellular response to testosterone?
a. The transcription of certain genes would decrease.
b. The activity of G proteins would decrease.
c. The cytoplasmic levels of cAMP would decrease.
d. The cytosolic calcium concentration would increase.
a. The transcription of certain genes would decrease.
Many G protein-coupled receptors contain seven transmembrane α-helical domains. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. Where would you expect to find the carboxyl end of the protein?
a. at the cytosolic surface
b. connected with the loop at H5 and H6
c. embedded in the phospholipid bilayer of the membrane
d. at the exterior surface
a. at the cytosolic surface
Many G protein-coupled receptors contain seven transmembrane α-helical domains. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. Where would a coupled G protein most likely interact with this receptor?
a. along the exterior margin
b. at the amino end
c. at the loop between H5 and H6
d. at the carboxyl end
c. at the loop between H5 and H6
Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?
a. receptor tyrosine kinase
b. ligand-gated ion channel
c. G protein-coupled receptor
d. steroid receptor
b. ligand-gated ion channel
Why does testosterone, a lipid-soluble signaling molecule that crosses the membranes of all cells, affect only target cells?
a. Only target cells retain the appropriate genes regulated by testosterone.
b. Intracellular receptors for testosterone are present only in target cells.
c. Only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor.
d. Only target cells possess the cytosolic enzymes that transduce the signal from testosterone to adenylyl cyclase.
b. Intracellular receptors for testosterone are present only in target cells.
If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?
a. It would use ATP instead of GTP to activate G proteins on the cytoplasmic side of the plasma membrane.
b. It would not be able to activate receptor tyrosine kinases.
c. It would be able to carry out reception and transduction but would not be able to respond to a signal.
d. It would not be able to activate G proteins on the cytoplasmic side of the plasma membrane.
d. It would not be able to activate G proteins on the cytoplasmic side of the plasma membrane.
Particular receptor tyrosine kinases (RTKs) that promote excessive cell division are found at high levels in various cancer cells. HER2 is an RTK that is present at excessively high levels in some breast cancer cells. Herceptin is a protein that binds to HER2 and inhibits cell division. Herceptin may be an effective treatment for breast cancer treatment under which of the following conditions?
a. If the patient has excessive levels of other RTKs in cancer cells.
b. If the patient's cancer cells have excessive levels of HER2.
c. If injection of HER2 in the patient's cancer cells stimulates cell division.
d. If the patient's genome codes for the HER2.
b. If the patient's cancer cells have excessive levels of HER2.
Which of the following activities would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins?
a. ligand-gated ion channel signaling pathways
b. receptor tyrosine kinase activity
c. binding of G proteins to G protein-coupled receptors
d. adenylyl cyclase activity
b. receptor tyrosine kinase activity
Not all intercellular signals require transduction. Which one of the following signals would be processed without transduction?
a. a signal that binds to the extracellular matrix
b. a lipid-soluble signal
c. a signal that is weakly bound to a nucleotide
d. a signal that binds to a receptor in the cell membrane
b. a lipid-soluble signal
What does it mean to say that a signal is transduced?
a. The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target.
b. The signal is amplified, such that even one signal molecule evokes a large response.
c. The signal triggers a sequence of phosphorylation events inside the cell.
d. The signal enters the cell directly and binds to a receptor inside.
a. The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target.
Which of the following processes generally requires protein phosphorylation?
a. activation of receptor tyrosine kinases
b. activation ligand-gated ion channels
c. activation of G protein-coupled receptors
d. activation of steroid hormone receptors
a. activation of receptor tyrosine kinases
A signal transmitted via phosphorylation of a series of proteins is generally associated with which of the following events?
a. activation of a ligand-gated ion channel
b. production of ATP in the process of signal transduction
c. conformational changes to each protein in the series
d. binding of a hormone to an intracellular receptor
c. conformational changes to each protein in the series
Which of the following is the most plausible explanation for why an animal cell would be unable to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid?
a. insufficient levels of protein kinase in the cell
b. insufficient ATP levels in the cytosol
c. excessive transport of calcium from the cytosol into the endoplasmic reticulum
d. inactivation of calcium-gated ion channels in the cell membrane
b. insufficient ATP levels in the cytosol
Which of the following results would most likely be an immediate result of a growth factor binding to its receptor?
a. adenylyl cyclase activity
b. protein kinase activity
b. cAMP activity
d. phosphorylase activity
b. protein kinase activity
The activity of adenylyl cyclase is essentially the opposite of which of the following enzymes?
A) protein kinase
B) protein phosphatase
C) phosphodiesterase
D) phosphorylase
C) phosphodiesterase
An inhibitor of which of the following enzymes could be used to block the release of calcium from the endoplasmic reticulum?
A) serine/threonine kinases
B) phosphodiesterase
C) phospholipase C
D) adenylyl cyclase
C) phospholipase C
Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of which of the following molecules?
A) phosphorylated proteins
B) cAMP
C) adenylyl cyclase
D) activated G proteins
B) cAMP
Protein kinase is an enzyme that functions in which of the following ways?
A) as a second messenger molecule
B) as a receptor for various signal molecules
C) activates or inactivates other proteins by adding a phosphate group to them
D) activates a G protein
C) activates or inactivates other proteins by adding a phosphate group to them
Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction?
A) tyrosines
B) glycine and histidine
C) serine and threonine
D) glycine and glutamic acid
C) serine and threonine
If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound that does which of the following?
A) activates epinephrine receptors in liver cells
B) increases cAMP production in liver cells
C) blocks G protein activity in liver cells
D) increases glycogen phosphorylase activity in liver cells
C) blocks G protein activity in liver cells
If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound that does which of the following?
A) increases glycogen phosphorylase activity in liver cells
B) activates adenylyl cyclase in liver cells
C) stimulates G protein activity in liver cells
D) increases phosphodiesterase activity in liver cells
D) increases phosphodiesterase activity in liver cells
Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP
The second messenger in this pathway is ________.
A) cAMP
B) G protein
C) adenylyl cyclase
D) G protein-coupled receptor
A) cAMP
Which of the following is true during a typical cAMP-mediated signal transduction event?
A) The second messenger is the last part of the system to be activated.
B) A hormone activates the second messenger by directly binding to it.
C) The second messenger amplifies the hormonal response by attracting more hormones to the cell being affected.
D) Adenylyl cyclase is activated after the hormone binds to the cell and before phosphorylation of proteins occurs.
D) Adenylyl cyclase is activated after the hormone binds to the cell and before phosphorylation of proteins occurs.
Put the steps of the process of signal transduction in the order they occur.
A conformational change in the signal-receptor complex activates an enzyme.
Protein kinases are activated.
A signal molecule binds to a receptor.
Target proteins are phosphorylated.
Second messenger molecules are released.
A) 1, 2, 3, 4, 5
B) 3, 1, 2, 4, 5
C) 3, 1, 5, 2, 4
D) 1, 2, 5, 3, 4
C) 3, 1, 5, 2, 4
Why can a signaling molecule cause different responses in different cells?
A. The transduction pathway in cells has a variable length.
B. Different cells possess different enzymes, which modify the signaling molecule into different molecules after it has arrived.
C. Different cells have membrane receptors that bind to different sides of the signaling molecule.
D. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor.
E. All of the above are correct.
D. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor.
What is a primary function of transcription factors?
A) They regulate the synthesis of DNA in response to a signal.
B) They convert ATP into cAMP.
C) They control gene expression.
D) They regulate the release of calcium from the endoplasmic reticulum.
C) They control gene expression.
What role do phosphatases play in signal transduction pathways?
A. They transfer a phosphate group from one protein in the pathway to the next molecule in the series.
B. They inactivate protein kinases to turn off signal transduction.
C. They amplify the second messenger cAMP.
D. They activate protein kinases by phosphorylation.
B. They inactivate protein kinases to turn off signal transduction.
Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because they ________.
A) are species specific
B) always lead to the same cellular response
C) amplify the original signal many times
D) counter the harmful effects of phosphatases
C) amplify the original signal many times
A mutation that knocks out the GTPase activity of a G protein would have what effect on a cell?
A) The concentration of available GTP would decrease.
B) The number of G proteins in the cell would increase.
C) The G protein would be inactivated by a G protein-coupled receptor/signal molecule complex.
D) The G protein would always be active.
D) The G protein would always be active.
Which of the following statements describes the events of apoptosis?
A) The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled.
B) The cell's DNA and organelles become fragmented, the cell dies, and it is phagocytized.
C) The cell's DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cell's parts are packaged in vesicles that are digested by specialized cells.
D) The cell's nucleus and organelles are lysed, and then the cell enlarges and bursts.
C) The cell's DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cell's parts are packaged in vesicles that are digested by specialized cells.
Which of the following provides the best evidence that cell-signaling pathways evolved early in the history of life?
A) Cell-signaling pathways are seen in "primitive" cells such as bacteria and yeast.
B) Bacteria and yeast cells signal each other in a process called quorum sensing.
C) Signal transduction molecules identified in distantly related organisms are similar.
D) Most signals in all types of cells are received by cell surface receptors.
C) Signal transduction molecules identified in distantly related organisms are similar.
Cells that are infected, damaged, or have reached the end of their functional life span often undergo "programmed cell death." This controlled cell suicide is called apoptosis. Select the appropriate description of this event on a cell's life cycle.
A) Apoptosis is regulated by cell surface receptors that signal when a cell has reached its density-dependent limits.
B) During apoptosis, dying cells leak out their contents, including digestive enzymes that also destroy healthy cells.
C) During apoptosis, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components of a cell.
D) Each cell organelle has protein signals that initiate the breakdown of the organelle's components, which leads to cell death.
C) During apoptosis, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components of a cell.
In a phosphorylation cascade (transduction pathway), a series of different molecules in a cell signaling pathway are phosphorylated. Each molecule adds a phosphate group to the next one in line. Protein phosphatases are enzymes that dephosphorylate each molecule returning the previous one to its inactive form. Use information from the figure to select which sentence best describes what would occur if the protein phosphatases were inhibited.
A. A signal would be sent since other enzymes could be used during the phosphorylation process.
B. Signals would continue to be sent as there is no mechanism to turn off the signal.
C. No signal would be sent since the phosphorylation cascade does not get initiated if the phosphatases are inhibited.
D. Only the initial signal would be sent, while all other signals would be blocked and transduction would be inhibited.
B. Signals would continue to be sent as there is no mechanism to turn off the signal.
Which statement correctly distinguishes the roles of protein kinases and protein phosphatases in signal transduction pathways?
a. Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.
b. Protein kinases are involved in signal transduction in unicellular eukaryotes such as yeast. Protein phosphatases are involved in signal transduction in multicellular eukaryotes.
c. Protein kinases are more critical than protein phosphatases to signal transduction enzymes.
a. Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.
Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways.
a. Relay proteins are the "first messengers," the extracellular signaling molecules that bind to the membrane receptor. The signal transduction pathways are then formed by the second messengers, which are the relay molecules that respond to the first messengers.
b. Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers.
c. Signal transduction pathways are multistep pathways in which relay proteins and second messengers alternate.
b. Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers.
Cyclic GMP, or cGMP, acts as a signaling molecule whose effects include relaxation of smooth muscle cells in artery walls. In the penis, this signaling pathway and the resulting dilation of blood vessels leads to an erection. Select the correct statement about the effect of Viagra on this signaling pathway.
A. Viagra prevents the formation of cGMP.
B. Viagra increases the rate of hydrolysis of cGMP to GMP.
C. Viagra inhibits the hydrolysis of cGMP to GMP.
C. Viagra inhibits the hydrolysis of cGMP to GMP.
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