Chapter 11

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. Hydrolysis of bound GTP by a G protein activates the G protein. C. A G protein bound to GDP is in its active state. 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.

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? A. Glycogen breakdown was observed only when epinephrine was administered to intact cells. B. Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined in a cell-free system. C. Epinephrine was known to have different effects on many types of cells. D. Receptor studies indicated that epinephrine was a ligand.

A. Glycogen breakdown was observed only when epinephrine was administered to intact cells.

In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following, if found in cells or organisms as they age, would provide evidence that this is related to cell signaling? A. Growth factor ligands do not bind as efficiently to receptors. B. Enzymatic activity declines. C. Hormone concentrations decrease. D. cAMP levels change very frequently.

A. Growth factor ligands do not bind as efficiently to receptors.

Why does testosterone, a lipid-soluble signaling molecule that crosses the membranes of all cells, affect only target cells? A. Intracellular receptors for testosterone are present only in target cells. B. Only target cells possess the cytosolic enzymes that transduce the signal from testosterone to adenylyl cyclase. C. Only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor D. Only target cells retain the appropriate genes regulated by testosterone.

A. Intracellular receptors for testosterone are present only in target cells.

How does the toxin of Vibrio cholerae cause profuse diarrhea? A. It modifies a G protein involved in regulating salt and water secretion B. It modifies a ligand-gated ion channel. C.It modifies adenylyl cyclase and triggers excess formation of cAMP. D.It signals IP3 to act as a second messenger for the release of calcium.

A. It modifies a G protein involved in regulating salt and water secretion

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 more critical than protein phosphatases to signal transduction enzymes C. Protein kinases are involved in signal transduction in unicellular eukaryotes such as yeast. Protein phosphatases are involved in signal transduction in multicellular eukaryotes.

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.

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. The target organ must have receptors that recognize and bind the hormone molecule. B. target organ must be the same as the organ that produced the hormone. C. The target organ must have the opposite mating type of the organ that produced the hormone.

A. The target organ must have receptors that recognize and bind the hormone molecule.

Why can a signaling molecule cause different responses in different cells? A. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor B. The transduction pathway in cells has a variable length. C. Different cells possess different enzymes, which modify the signaling molecule into different molecules after it has arrived. D. Different cells have membrane receptors that bind to different sides of the signaling molecule.

A. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor

In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function? A. aggregation of bacteria that can cause cavities B. formation of mating complexes C. secretion of substances that Inhibit foreign bacteria D. digestion of unwanted parasite populations

A. aggregation of bacteria that can cause cavities

To what does the term "ligand" refer in cell biology? A. any small molecule that can bind in a specific manner to a larger one B. the bond that forms between a signaling molecule and its receptor C. a molecule that can occupy a receptor site while not activating the receptor D. the change in shape that occurs when a signaling molecule binds to its receptor

A. any small molecule that can bind in a specific manner to a larger one

A signal transmitted via phosphorylation of a series of proteins is generally associated with which of the following events? A. conformational changes to each protein in the series B. binding of a hormone to an intracellular receptor C. activation of a ligand-gated ion channel D. production of ATP in the process of signal transduction

A. conformational changes to each protein in the series

What is apoptosis? A. controlled cell suicide B. a type of second messenger C. a way to stimulate transcription D. a metabolic step in blood clotting

A. controlled cell suicide

Viagra causes dilation of blood vessels and increased blood flow to the penis, facilitating erection. Viagra acts by inhibiting which of the following events? A. hydrolysis of cGMP to GMP B. hydrolysis of GTP to GDP C. dephosphorylation of cGMP D. formation of cGMP from GTP

A. hydrolysis of cGMP to GMP

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. actin microfilaments C. receptor tyrosine kinases D. fibronectins

A. integrins

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. growth factor receptors C. nucleosomes

A. transcription factors

Protein phosphorylation is commonly involved with all of the following except A.activation of G protein-coupled receptors. B. regulation of transcription by extracellular signaling molecules. C. activation of protein kinase molecules. D. enzyme activation.

A.activation of G protein-coupled receptors.

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? A. Enzymatic activity was proportional to the amount of calcium added to a cell-free extract. B. Glycogen breakdown was observed only when epinephrine was administered to intact cells. C. Glycogen breakdown was observed only when epinephrine and glycogen phosphorylase were mixed. D. Receptor studies indicated that epinephrine was a ligand.

B. Glycogen breakdown was observed only when epinephrine was administered to intact cells.

Which of the following is a substance that acts at a long distance from the site at which it is secreted? A. neurotransmitter B. hormone C. paracrine signal D. synaptic signal

B. Hormone

Which property is necessary for protein A to bind to protein B? A. Protein A and Protein B must be identical so they can form a pair. B. Protein A must have regions of shape and charge that are complementary to those on Protein B. C. Protein A must have regions of shape and charge that are the same as those on Protein B. D. Any two molecules can bind to each other; there is no special property required.

B. Protein A must have regions of shape and charge that are complementary to those on Protein B.

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 inhibits the hydrolysis of cGMP to GMP. C. Viagra increases the rate of hydrolysis of cGMP to GMP

B. Viagra inhibits the hydrolysis of cGMP to GMP.

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → AMP. Identify the second messenger. A. adenylyl cyclase B. cAMP C. GTP D. G protein

B. cAMP

The activity of adenylyl cyclase is essentially the opposite of which of the following enzymes? A. Protein kinase B. phosphodiesterase C. phosphorylase D. protein phosphatase

B. phosphodiesterase

An inhibitor of which of the following enzymes could be used to block the release of calcium from the endoplasmic reticulum? A. phosphodiesterase B. phospholipase C C. adenylyl cyclase D. serine/threonine kinases

B. phospholipase C

Why are there often so many steps between the original signal event and the cell's response? A. Each transduction is a checkpoint. B.Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses C. The accumulation of genetic mutations over time has added redundant steps to the pathway. D. Long, highly specific pathways minimize the possibility that a relay molecule accidentally could activate a pathway leading to a secondary response

B.Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses

How does hydrolysis of ATP drive transport? A. The transport protein synthesizes ATP as it transports ions down their concentration gradient across the membrane. B. ATP hydrolysis moves protons across the membrane and the proton-motive force is used to transport substances. C. A phosphate group from ATP is added to a transport protein, changing its shape and facilitating transport. D. Transport cannot be driven by ATP hydrolysis—substances are transported through channels in channel proteins. D.

C. A phosphate group from ATP is added to a transport protein, changing its shape and facilitating transport.

Sutherland discovered that the signaling molecule epinephrine is responsible for which of the following events? A. Decreasing blood glucose levels. B. Interacting directly with glycogen phosphorylase. C. Elevating cytosolic concentrations of cyclic AMP. D. Stimulating glycogen synthesis.

C. Elevating cytosolic concentrations of cyclic AMP.

Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways. A. Signal transduction pathways are multistep pathways in which relay proteins and second messengers alternate. B. 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. C. 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 that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers

Which of the following statements describes the events of apoptosis? A.The cell's nucleus and organelles are lysed, and then the cell enlarges and bursts. B. The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled. 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 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.

You have isolated a previously unstudied protein, identified its complete structure in detail, and determined that it is an enzyme that catalyzes the breakdown of a large substrate. You notice it has two binding sites: one large and one small. Speculate about how this enzyme might function. A. The enzyme catalyzes two different reactions, each with its own specific substrate. B. It is probably a cell membrane transport protein—like an ion channel. C. The small site is probably a binding site for a small molecule whose binding affects the enzyme's shape and function—its breakdown of the large substrate

C. The small site is probably a binding site for a small molecule whose binding affects the enzyme's shape and function—its breakdown of the large substrate

What is a primary function of transcription factors? A. They convert ATP into cAMP B. They regulate the synthesis of DNA in response to a signal. 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 amplify the second messenger cAMP. B. They transfer a phosphate group from one protein in the pathway to the next molecule in the series. C. They inactivate protein kinases to turn off signal transduction. D. They activate protein kinases by phosphorylation.

C. They inactivate protein kinases to turn off signal transduction.

In yeast signal transduction, a yeast cell releases a mating factor, which ________. A.acts back on the same cell that secreted the mating factor, changing its development B.passes through the membranes of neighboring cells, binds to DNA, and initiates transcription C.binds to receptors on the membranes of other types of yeast cells D. diffuses through the membranes of distant cells, causing them to produce factors that initiate long-distance migrations

C. binds to receptors on the membranes of other types of yeast cells

What is the function of tyrosine-kinase receptors? A. Enzymatic hydrolyzing of the signaling molecule shortly after its arrival B. enzymatic degrading of GTP to GDP C. enzymatic phosphorylation of tyrosine in the receptor protein D. allowing specific ions to enter the cell after ligand binding

C. enzymatic phosphorylation of tyrosine in the receptor protein

What are scaffolding proteins? A.relay proteins that orient receptors and their ligands in appropriate directions to facilitate complex formation B. proteins that enter the nucleus of a cell to regulate transcription C. large molecules to which several relay proteins attach to facilitate cascade effects D. microtubule arrays that allow lipid-soluble hormones to get from the cell membrane to the nuclear pores

C. large molecules to which several relay proteins attach to facilitate cascade effects

Which of the following activities would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins? A. adenylyl cyclase activity B. ligand-gated ion channel signaling pathways C. receptor tyrosine kinase activity D. binding of G proteins to G protein-coupled receptors

C. receptor tyrosine kinase activity

Which of the following is a correct association? A. phosphodiesterase activity and the removal of phosphate groups B.adenylyl cyclase activity and the conversion of cAMP to AMP C. kinase activity and the addition of a tyrosine D. GTPase activity and hydrolysis of GTP to GDP

D. GTPase activity and hydrolysis of GTP to GDP

Apoptosis involves all but which of the following? A. digestion of cellular contents by scavenger cells B. cell-signaling pathways C. fragmentation of the DNA D. Lysis of the cell

D. Lysis of the cell

Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life? A. The pathways in primitive organisms, such as bacteria, are short, whereas those in advanced forms, such as mammals, are long. B. Cell signaling is observed in organisms that do not utilize sexual reproduction. C. Simple forms of life, such as prokaryotic cells, utilize cell signaling. D. The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

D. The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

What does it mean to say that a signal is transduced? A. The signal triggers a sequence of phosphorylation events inside the cell. B. The signal is amplified, such that even one signal molecule evokes a large response. C. The signal enters the cell directly and binds to a receptor inside. D. The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target.

D. The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target.

Which of the following statements is true of steroid receptors? A. Steroid receptors are typically bound to the external surface of the nuclear membrane. B. The receptor molecules are themselves lipids or glycolipids. C. The unbound steroid receptors are quickly recycled by lysosomes. D. The receptor may be inside the nucleus of a target cell.

D. The receptor may be inside the nucleus of a target cell.

Not all intercellular signals require transduction. Which one of the following signals would be processed without transduction? A. signal that binds to a receptor in the cell membrane B. a signal that is weakly bound to a nucleotide C. a signal that binds to the extracellular matrix D. a lipid-soluble signal

D. a lipid-soluble signal

Which of the following are among the most common second messengers? A. kinase and phosphatase B. kinase and phosphate groups C. G proteins and GTP D. calcium ion and cAMP

D. calcium ion and cAMP

The activation of receptor tyrosine kinases is characterized by A. GTP hydrolysis. B. dimerization and IP3 binding. C. channel protein shape change. D. dimerization and phosphorylation.

D. dimerization and phosphorylation.

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. stimulates G protein activity in liver cells C. activates adenylyl cyclase in liver cells D. increases phosphodiesterase activity in liver cells

D. increases phosphodiesterase activity in liver cells

Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because A. only target cells possess the cytosolic enzymes that transduce the testosterone. B. most cells lack the Y chromosome required. C. only target cells retain the appropriate DNA segments. D. intracellular receptors are present only in target cells.

D. intracellular receptors are present only in target cells.

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. phosphorylated receptor tyrosine kinase dimer B. intracellular receptor C. receptor tyrosine kinase D. ligand-gated ion channel E. G protein-coupled receptor

D. ligand-gated ion channel

The cholera bacterium Vibrio cholerae produces an enzyme toxin that chemically modifies a G protein involved in regulating salt and water secretion in intestinal cells. Stuck in its active form, the modified G protein stimulates the production of a high concentration of cAMP, which causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis. An infected person quickly develops profuse diarrhea and if left untreated can soon die from the loss of water and salts. What is the basic effect of the cholera toxin?

The basic effect of the cholera toxin is signal amplification.

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?

at the loop between H5 and H6