Chapter 11

Which of these is responsible for initiating a signal transduction pathway? A. A B. B C. C D. D E. E

A. A

Which of the following is true during a typical cAMP-mediated signal transduction event? A. Adenylyl cyclase is activated after the hormone binds to the cell and before phosphorylation of proteins occurs. B. A hormone activates the second messenger by directly binding to it. C. The second messenger is the last part of the system to be activated. D. The second messenger amplifies the hormonal response by attracting more hormones to the cell being affected.

A. Adenylyl cyclase is activated after the hormone binds to the cell and before phosphorylation of proteins occurs.

Which of these is an ion-channel receptor? A. D B. A C. E D. C E. B

A. D

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. During apoptosis, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components of a cell. B. Apoptosis is regulated by cell surface receptors that signal when a cell has reached its density-dependent limits. C. During apoptosis, dying cells leak out their contents, including digestive enzymes that also destroy healthy cells. D. Each cell organelle has protein signals that initiate the breakdown of the organelle's components, which leads to cell death.

A. During apoptosis, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components of a cell.

In the nematode C. elegans, ced-9 prevents apoptosis in a normal cell in which of the following ways? A. It prevents the caspase activity of ced-3 and ced-4. B. Ced-9 prevents blebbing by its action on the cell membrane. C. Ced-9 remains inactive until it is signaled by ced-3 and other caspases. D. Ced-9 cleaves to produce ced-3 and ced-4.

A. It prevents the caspase activity of ced-3 and ced-4.

Which of the following provides the best evidence that cell-signaling pathways evolved early in the history of life? A. Signal transduction molecules identified in distantly related organisms are similar. B. Most signals in all types of cells are received by cell surface receptors. C. Bacteria and yeast cells signal each other in a process called quorum sensing. D. Cell-signaling pathways are seen in "primitive" cells such as bacteria and yeast.

A. Signal transduction molecules identified in distantly related organisms are similar.

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 enters the cell directly and binds to a receptor inside. C. The signal triggers a sequence of phosphorylation events inside the cell. D. The signal is amplified, such that even one signal molecule evokes a large response.

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

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.

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. receptor tyrosine kinases C. fibronectins D. actin microfilaments

A. integrins

Which of the following types of signaling is represented in the figure? A. paracrine B. hormonal C. autocrine D. synaptic

A. paracrine

Which of the following is a type of local signaling in which a cell secretes a signal molecule that affects neighboring cells? A. paracrine signaling B. synaptic signaling C. autocrine signaling D. hormonal signaling

A. paracrine signaling

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

A. phosphodiesterase

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. receptor tyrosine kinases B. steroid receptors C. G protein-coupled receptors D. ligand-gated ion channels

A. receptor tyrosine kinases

Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction? A. serine and threonine B. tyrosines C. glycine and histidine D. glycine and glutamic acid

A. serine and threonine

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. relay molecule C. transducer D. response molecule

A. signal molecule

Which of these is a receptor tyrosine kinase? A. B B. C C. E D. A E. D

B. C

Which of the following statemnts about a G protein signaling pathway is true? A. A G protein-coupled receptor bound to GTP is in its active state. B. A G protein bound to GTP is in its active state. C. A G protein bound to GDP is in its active state. D. Hydrolysis of bound GTP by a G protein activates the G protein.

B. A G protein bound to GTP is in its active state.

Which of these is a membrane receptor? A. A B. B C. C D. D E. E

B. B

Why has C. elegans proven to be a useful model for understanding apoptosis? A. C. elegans does not naturally use apoptosis, but can be induced to do so in the laboratory. B. C. elegans undergoes a fixed and easy-to-visual number of apoptotic events during its normal development. C. C. elegans has large cells wherein apoptosis is easily observed without the aid of a microscope. D. As C. elegans ages, its cells die progressively until the whole organism is dead.

B. C. elegans undergoes a fixed and easy-to-visual number of apoptotic events during its normal development.

Which of these extracellular signal molecules could diffuse through a plasma membrane and bind to an intracellular receptor? A. starch B. estrogen C. glucose D. cellulose E. glycerol

B. Estrogen

Why does testosterone, a lipid-soluble signaling molecule that crosses the membranes of all cells, affect only target cells? A. 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. 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.

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

What is the most likely mechanism by which testosterone functions inside a cell? A. It acts as a steroid signal receptor that activates ion channel proteins in the plasma membrane. B. It binds with a receptor protein that enters the nucleus and activates expression of specific genes. C. It coordinates a phosphorylation cascade that reduces spermatogenesis. D. It acts as a signal receptor that activates tyrosine kinases.

B. It binds with a receptor protein that enters the nucleus and activates expression of specific genes.

If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system? A. It would not be able to activate receptor tyrosine kinases. B. It would not be able to activate G proteins on the cytoplasmic side of the plasma membrane. C. It would use ATP instead of GTP to activate G proteins on the cytoplasmic side of the plasma membrane. D. It would be able to carry out reception and transduction but would not be able to respond to a signal.

B. It would not be able to activate G proteins on the cytoplasmic side of the plasma membrane.

_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell's cytoplasm. A. Adenylyl cyclase ... cyclic AMP ... Ca2+ B. Phospholipase C ... IP3 .... Ca2+ C. Protein kinase ... PIP2 ... Na+ D. Phospholipase C ... cyclic AMP ... Ca2+ E. Adenylyl cyclase ... IP3 .... Ca2+

B. Phospholipase C ... IP3 .... Ca2+

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

B. 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. a signal that is weakly bound to a nucleotide B. a lipid-soluble signal C. a signal that binds to the extracellular matrix D. a signal that binds to a receptor in the cell membrane

B. a lipid-soluble signal

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. binds to receptors on the membranes of other types of yeast cells C. passes through the membranes of neighboring cells, binds to DNA, and initiates transcription D. diffuses through the membranes of distant cells, causing them to produce factors that initiate long-distance migrations

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

The cleavage of glycogen by glycogen phosphorylase releases _____. A. nothing: glycogen phosphorylase cannot cleave glycogen B. glucose-1-phosphate C. galactose-1-phosphate D. fructose-1-phosphate E. cellulose

B. glucose-1-phosphate

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. excessive transport of calcium from the cytosol into the endoplasmic reticulum B. insufficient ATP levels in the cytosol C. inactivation of calcium-gated ion channels in the cell membrane D. insufficient levels of protein kinase in the cell

B. insufficient ATP levels in the cytosol

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

B. 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. 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

Put the steps of the process of signal transduction in the order they occur. 1. A conformational change in the signal-receptor complex activates an enzyme. 2. Protein kinases are activated. 3. A signal molecule binds to a receptor. 4. Target proteins are phosphorylated. 5. Second messenger molecules are released. A. 3, 1, 2, 4, 5 B. 1, 2, 3, 4, 5 C. 3, 1, 5, 2, 4 D. 1, 2, 5, 3, 4

C. 3, 1, 5, 2, 4

The binding of signal molecules to _____ results in the phosphorylation of tyrosines. A. A B. D C. C D. B E. E

C. C

At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogen and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects? A. Each cell responds in the same way when steroids bind to the cell surface. B. Estrogen is produced in very large concentration by nearly every tissue of the body. C. Estrogen binds to specific receptors inside many kinds of cells, each with different responses. D. Estrogen is kept away from the surface of any cells, not able to bind it at the surface.

C. Estrogen binds to specific receptors inside many kinds of cells, each with different responses.

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

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

The receptors for steroid hormones are located inside the cell instead to the membrane surface like most other signal receptors this is not a problem for steroids because ________ A. Steroid hormones receptors undergo conformational changes that relocate them on the membrane. B. Both steroid hormones and their receptors are produced by the same cells. C. Steroid hormones are lipid soluble, so they can readily diffuse through the lipid bilayer of the cell. D. Steroid hormones first bind to a steroid activator and this complex is transported across the cell membrane.

C. Steroid hormones are lipid soluble, so they can readily diffuse through the lipid bilayer of the cell.

What is a primary function of transcription factors? A. They regulate the release of calcium from the endoplasmic reticulum. B. They convert ATP into cAMP. C. They control gene expression. D. They regulate the synthesis of DNA in response to a signal.

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 amplify the second messenger cAMP. 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.

Yeast cells of mating type a, are genetically engineered to produce only mating factor a instead 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 a cells. B. They will only mate with normal mating type alpha cells. C. They will mate each other or with normal mating type a cells, but not with normal mating type alpha cells. . D. They will only mate each other and not with normal mating type a or alpha cells.

C. They will mate each other or with normal mating type a cells, but not with normal mating type alpha cells.

A protein kinase activating many other protein kinases is an example of _____. A. deactivation B. a cellular response C. amplification E. sensitization

C. amplification

If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound that A. activates epinephrine receptors in liver cells B. increase 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

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. activated G proteins C. cAMP D. adenylyl cyclase

C. cAMP

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. increases phosphodiesterase activity in liver cells D. activates adenylyl cyclase in liver cells

C. increases phosphodiesterase activity in liver cells

Binding of a signlaing molecule to which type of receptor leads directyl to a change in the distribution of ions on opposite sides of the membrane? A. receptor tyrosine kinase B. G protein-coupled receptor C. ligand-gated ion channel D. steroid receptor

C. ligand-gated ion channel

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

Which of these is a G-protein-linked receptor? A. D B. C C. B D. A E. E

D. A

Which of these is a receptor molecule? A. A B. E C. D D. B E. C

D. B

What role does a transcription factor play in a signal transduction pathway? A. By binding to a plasma membrane receptor it initiates a cascade. B. It relays a signal from the cytoplasm to the plasma membrane. C. It activates relay proteins. D. By binding to DNA it triggers the transcription of a specific gene. E. It is a plasma membrane protein that binds signal molecules.

D. By binding to DNA it triggers the transcription of a specific gene.

Which of these is NOT correct? A. Tyrosine-kinase receptors consist of two polypeptides that join when activated by a signal molecule. B. Ion channels are found on both the plasma membrane and the endoplasmic reticulum. C. Kinases are enzymes that phosphorylate other molecules. D. Cyclic AMP binds to calmodulin. E. Phospholipase C catalyzes the formation of IP3.

D. Cyclic AMP binds to calmodulin.

Which of these receptor molecules would allow Na+ to flow into the cell? A. A B. C C. E D. D

D. D

Which of these receptors is NOT a membrane receptor? A. C B. D C. A D. E

D. E

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

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

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's genome codes for the HER2. B. If injection of HER2 in the patient's cancer cells stimulates cell division. C. If the patient has excessive levels of other RTKs in cancer cells. D. If the patient's cancer cells have excessive levels of HER2.

D. If the patient's cancer cells have excessive levels of HER2.

Which of the following statements is true of signal molecule? A. When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules. B. In response to some G protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium. C. In most cases, signal molecules interact with the cell at the plasma membrane, enter the cell, and eventually enter the nucleus. D. Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

D. Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

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 nucleus and organelles are lysed, and then the cell enlarges and bursts. C. The cell's DNA and organelles become fragmented, the cell dies, and it is phagocytized. D. 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 shrinks and forms blebs, and the cell's parts are packaged in vesicles that are digested by specialized 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. The target organ must be the same as the organ that produced the hormone. B. The target organ must have the opposite mating type of the organ that produced the hormone. C. Cells in the target organ must modify their plasma membranes to allow the hormone to enter the cytoplasm. D. The target organ must have receptors that recognize and bind the hormone molecule.

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

Protein kinase is an enzyme that functions in which of the following ways? A. activates a G protein B. as a second messenger molecule C. as a receptor for various signal molecules D. activates or inactivates other proteins by adding a phosphate group to them

D. activates or inactivates other proteins by adding a phosphate group to them

Which of the following processes generally requires protein phosphorylation? A. activation ligand-gated ion channels B. activation of G protein-coupled receptors C. activation of steroid hormone receptors D. activation of receptor tyrosine kinases

D. activation of receptor tyrosine kinases

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because they _____. A. always lead to the same cellular response B. counter the harmful effects of phosphatases C. are species specific D. amplify the original signal many times

D. amplify the original signal many times

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. connected with the loop at H5 and H6 B. embedded in the phospholipid bilayer of the membrane C. at the exterior surface D. at the cytosolic surface

D. 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. at the amino end B. at the carboxyl end C. along the exterior margin D. at the loop between H5 and H6

D. at the loop between H5 and H6

Calcium ions that act as second messengers are stored in _____. A. lysosomes B. chloroplasts C. mitochondria D. endoplasmic reticula E. peroxisomes

D. endoplasmic reticula

A(n) _____ is an example of a signal molecule that can bind to an intracellular receptor and thereby cause a gene to be turned on or off. A. ion B. protein C. carbohydrate D. steroid E. nucleic acid

D. steroid

Which of these is a signal molecule? A. B B. C C. E D. D E. A

E. A

Which of these acts as a second messenger? A. E B. B C. A D. C E. D

E. D

A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors. A. steroid B. intracellular C. receptor tyrosine kinase D. ion-channel E. G-protein-linked

E. G-protein-linked

Epinephrine acts as a signal molecule that attaches to _____ proteins. A. nuclear receptor B. intracellular receptor C. receptor tyrosine kinase D. ion-channel receptor E. G-protein-linked receptor

E. G-protein-linked receptor

Which of these is activated by calcium ions? A. IP3 B. PIP2 C. G protein D. adenylyl cyclase E. calmodulin

E. calmodulin

Which of these acts as a second messenger? A. G-protein-linked receptor B. adenylyl kinase C. protein kinase D. G protein E. cyclic AMP

E. cyclic AMP

Thyroid hormones bind to _____ receptors. A. plasma membrane ion-channel B. tyrosine-kinase C. G-protein-linked E. intracellular F. steroid

E. intracellular

A signal molecule is also known as a(n) _____.

Ligand

A signal transduction pathway is initiated when a _____ binds to a receptor.

Signal Molecule

Which of these is the second of the three stages of cell signaling?

Transduction