Evidence that cell signaling evolved early in the history of life comes from _____. (eText Concept 11.1)

A. comparative studies of mitochondrial DNA
B. comparative studies of ribosomal RNA
C. the fossil record
D. the study of protein receptors embedded in the nuclear membrane
E. the similarity of the mechanisms in organisms that have a very distant common ancestor

When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example thromboxane A2 is acting as a _____. (eText Concept 11.1)

A. neurotransmitter
B. transcription factor
C. protein kinase
D. local regulator
E. G protein

Early work on signal transduction and glycogen metabolism by Sutherland indicated that _____. (eText Concept 11.1)

A. the signal molecule combined directly with a cytosolic enzyme to form an active quaternary structure
B. the signal molecule worked equally well with intact or disrupted cells
C. the signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated
D. the cell-signaling pathway involves two separate steps: transduction and response
E. epinephrine is involved in response to stress

Certain yeast cells secrete a molecule called the α factor. The purpose of this molecule is to _____. (eText Concept 11.1)

A. kill other yeast cells nearby, which may be competing for access to food
B. kill bacteria nearby, which may be competing for access to food
C. stimulate an A yeast cell to grow toward the α cell
D. attract other yeast cells of the same mating type to assemble
E. enzymatically process food into a form that can be easily absorbed

Cells use different signaling strategies to achieve different goals. In hormonal signaling _____. (eText Concept 11.1)

A. numerous cells can receive and respond to a signal produced in their vicinity
B. the signal can be directed to a very specific target because a narrow space separates the target cell from the transmitting cell
C. a concentration gradient between the signaling cell and its target cells is established, causing cells along the gradient to respond in different ways
D. specialized cells release hormone molecules into the circulatory system, permitting distant cells to be affected
E. special molecules are passed through cell junctions

Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence? (eText Concept 11.2)

A. Nontarget cells possess enzymes that immediately degrade the molecules as they enter the cell.
B. Nontarget cells lack the inactive enzymes that the signal molecules activate.
C. Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell’s nucleus.
D. The signal molecules diffuse from the cell before an effective concentration can be achieved.
E. In nontarget cells, these signal molecules cross the membranes of the endoplasmic reticulum and are captured by vesicles.

Different types of cells can respond differently to the same signaling molecule. Which of the following explains this apparent paradox? (eText Concept 11.2)

A. Different types of cells possess different genomes.
B. Different types of cells possess different proteomes.
C. Different types of cells possess different types of phospholipids in their plasma membranes.
D. Different cells have different patterns of carbohydrates on their cell surfaces.
E. Nuclear envelope proteins vary from cell type to cell type and this means that cells respond to signaling molecules differently.

Steroid hormones can enter a cell by simple diffusion. Therefore steroids _____. (eText Concept 11.2)

A. are not an example of signaling molecules
B. do not bind to receptors
C. directly bind to DNA
D. do not initiate cell signaling by interacting with a receptor in the plasma membrane
E. act by phosphorylating DNA

Steroid hormones can enter a cell by simple diffusion. Therefore steroids _____. (eText Concept 11.2)

A. move up a concentration gradient and are nonpolar
B. move up a concentration and are polar
C. move down a concentration gradient and are polar
D. move through a channel, down a gradient, and are nonpolar
E. None of the listed responses is correct.

A small molecule that specifically binds to a larger molecule is called a(n) _____. (eText Concept 11.2)

A. α protein
B. ligand
C. protein kinase
D. competitive inhibitor

Receptors for signal molecules _____. (eText Concept 11.2)

A. all work via protein kinases
B. are never found in the nucleus of a cell
C. may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus
D. all work by opening ion channels
E. are only found associated with the plasma membrane

Testosterone does not affect all cells of the body because _____. (eText Concept 11.2)

A. testosterone cannot cross the plasma membrane
B. not all cells in the body have membrane receptors for testosterone
C. it is a local regulator
D. it affects only cells that have ion-channel receptors
E. not all cells have cytoplasmic receptors for testosterone

G-protein-linked receptors _____, whereas receptor tyrosine kinases _____. (eText Concept 11.2)

A. act by phosphorylating a protein … open an ion channel when bound to a signal molecule
B. are transmembrane proteins … are found only on the cytoplasmic side of the plasma membrane
C. are not enzymes … have enzymatic function
D. form a dimer when activated … catalyze the transfer of a phosphate group from ATP to an amino acid
E. phosphorylate the amino acid guanine … phosphorylate the amino acid threonine

Which of the following is activated when the binding of single molecules causes it to form a dimer? (eText Concept 11.2)

A. ion-channel receptors
B. protein phosphatase receptors
C. G-protein-linked receptors
D. adenylyl cyclase receptors
E .receptor tyrosine kinases

The binding of a signal molecule to a ligand-gated ion channel _____. (eText Concept 11.2)

A. causes the ion channel to phosphorylate an amino acid on a target molecule
B. results in the formation of ion-channel dimers
C. promotes the binding of a steroid hormone to its receptor in the cytoplasm
D. alters the expression of genes, especially in neurons
E. affects the membrane potential

Nitric oxide is unusual among animal signal molecules in that it _____. (eText Concept 11.2)

A. enters the cell via a protein channel
B. acts by directly binding to DNA
C. binds to membrane receptors and cytoplasm receptors
D. is a gas
E. activates proteins by removing phosphate

A G protein is active when _____. (eText Concept 11.2)

A. GDP replaces GTP
B. it is bound by its ligand and transported to the nucleus
C. GTP is bound to it
D. it is phosphorylated by protein kinase
E. Ca2+ binds to a G-protein-linked receptor

If a modified form of GTP that cannot be enzymatically converted to GDP were added to a culture of cells, the likely result would be _____. (eText Concept 11.2)

A. the inactivation of ligand-gated ion channels
B. the inactivation of G-protein-linked signaling pathways
C. that the activated G proteins would remain locked in the “on” position, transmitting signal even in the absence of a signaling molecule
D. the inhibition of pathways stimulated by tyrosine-kinase receptors
E. receptor tyrosine kinases would be stimulated by the additional phosphate groups present in the modified GTP

What event would activate a G protein? (eText Concept 11.2)

A. hydrolysis of GTP to GDP
B. hydrolysis of GDP to GTP
C. phosphorylation of GDP to GTP
D. replacement of GDP with GTP
E. phosphorylation of GTP to GDP

Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer. Ras normally signals to a cell that it should divide. Cancer cells divide uncontrollably. Which of the following changes to Ras would you expect to see in a cancer cell that has mutated Ras present? (eText Concept 11.2)

A. a mutation that leads to Ras being sent to the endomembrane system
B. a mutation that means Ras cannot bind to GTP
C. a mutation that means Ras cannot hydrolyze GTP to GDP
D. a mutation that means GDP is constantly bound to Ras
E. a mutation in which Ras cannot bind to its GPCR

The cellular response of a signal pathway that terminates at a transcription factor would be _____. (eText Concept 11.2)

A. the synthesis of mRNA
B. the activation of an inactive enzyme
C. alteration of the cytoskeleton
D. a change in the chemical composition of the cytosolic environment
E. the activation of a metabolic pathway

Cholera develops when the bacterial toxin _____. (eText Concept 11.3)

A. inhibits the enzyme that normally breaks down cAMP
B. prevents G-protein inactivation, which leads to the continuous production of cAMP
C. inhibits adenylyl cyclase, preventing the cell from producing cAMP
D. blocks the receptor site for cAMP
E. phosphorylates the cAMP, producing ADP

What did Sutherland discover about glycogen metabolism in liver cells? (eText Concept 11.3)

A. Glucagon breaks down glycogen to glucose in liver cells.
B. The hormone that breaks down glycogen into glucose enters the liver cell.
C. The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell.
D. Glucose is produced from glycogen when epinephrine binds to a cytoplasmic protein.
E. A cytoplasmic receptor triggers the signal transduction pathway that produces glucose from glycogen.

The general name for an enzyme that transfers phosphate groups from ATP to a protein is _____. (eText Concept 11.3)

A. protein dehydrogenase
B. protein phosphatase
C. protein kinase
D. peptidase
E. protein cyclase

ATPgammaS is a form of ATP that cannot be hydrolyzed by enzymes. If this compound was introduced to cells so that it replaced the normal ATP present in the cell, which of the following would you predict? (eText Concept 11.3)

A. an increase in the numbers of phosphorylated proteins in the cell
B. an increase in anabolic cellular reactions
C. a decrease in phosphorylated proteins in the cell
D. an increase in cell division
E. Two of the listed responses would be expected.

Phosphorylation _____. (eText Concept 11.3)

A. always inactivates a protein
B. activates G-protein-linked receptors
C. can either activate or inactivate a protein
D. is accomplished by protein phosphatases
E. always activates a protein

The source of phosphate for a phosphorylation cascade is _____. (eText Concept 11.3)

C. protein kinase
E. protein phosphatase

Second messengers tend to be water-soluble and small. This accounts for their ability to _____. (eText Concept 11.3)

A. rapidly cross the plasma membrane
B. rapidly move throughout the cell by diffusion
C. pass quickly from cell to cell
D. move from substrate to substrate during a phosphorylation cascade
E. cross the nuclear membrane and interact with DNA

cAMP usually directly activates _____. (eText Concept 11.3)

A. phosphodiesterase
B. receptor tyrosine kinases
C. G proteins
D. adenylyl cyclase
E. protein kinase A

A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to _____. (eText Concept 11.3)

A. an increase in the amount of cAMP present in the cell
B. lower activity of protein kinase A
C. higher activity of protein kinase A
D. reduced binding of adenylyl cyclase to protein kinase A
E .increased binding of adenylyl cyclase to the G protein that activates it

Domoic acid is a neurotoxin produced by some species of alga. Domoic acid binds to the kainate receptor on neurons in parts of the brain. The kainate receptor facilitates the movement of calcium into the cell. Excess domoic acid-induced stimulation of the neural kainate receptors causes neural damage and short-term memory loss. Based on this, which of the following is likely true? (eText Concept 11.3)

A. The kainate receptor is a ligand-gated ion channel and domoic acid is a ligand.
B. Calcium is actively pumped into the cell by the kainate receptor.
C. The kainate receptor is a GPCR that stimulates adenylate cyclase to produce cAMP that serves to amplify the signal, and to speed the signal’s transduction through the cytoplasm.
D. The first two listed responses are correct.
E .The second and third responses are correct.

During the transduction of a signal, one molecule or ion may be closely associated with the activity of another. Select the pair that is correctly combined. (eText Concept 11.3)

A. calcium, IP3
B. cAMP, adenylyl cyclase
C. cAMP, protein kinase A
E. All of the listed responses are correct.

A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that cAMP _____ and Ca2+ _____. (eText Concept 11.3)

A. is always present at high levels in the cytosol … is present at low levels in the absence of a signal
B. is synthesized by an enzyme in response to a signal … is released from intracellular stores
C. is stored in the endoplasmic reticulum … is never stored in the cell
D. is tyrosine-kinase-receptor linked … is G-protein-receptor linked

IP3 (inositol trisphosphate) is produced as a result of _____. (eText Concept 11.3)

A. protein kinase A activation
B. Ca2+
C. the cleavage of a certain kind of phospholipid in the plasma membrane
E .phospholipase C

IP3 (inositol trisphosphate) acts by _____. (eText Concept 11.3)

A. activating cAMP
B. phosphorylating signal receptors
C. opening Ca2+ channels
D. activating PIP2
E. activating DAG

Which of the following is NOT a potential source of Ca2+ that can be released into the cytoplasm? (eText Concept 11.3)

A. blood
B. extracellular fluid
C. mitochondria
D. endoplasmic reticulum
E. lysosomes

In eukaryotic cells, which of the following is a second messenger that is produced as a response to an external signal such as a hormone? (eText Concept 11.3)

A .glycogen
B. cyclic AMP
D. epinephrine
E. glucose

In the inherited disorder Wiskott-Aldrich syndrome, _____. (eText Concept 11.4)

A. muscle cells lack the appropriate membrane receptor
B. a multifunctional relay protein involved with the proliferation of immune cells is defective
C. nerve cells lack the ability to produce cAMP
D. G proteins are unable to phosphorylate GDP
E. the endoplasmic reticulum is unable to store calcium

In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, _____. (eText Concept 11.4)

A. the signal is reduced
B. the number of molecules involved decreases
C. the number of molecules involved remains constant
D. the signal is amplified
E. glycogenesis is stimulated

Cells of the gastrointestinal (GI) tract and cells of the heart respond differently to epinephrine because _____. (eText Concept 11.4)

A. there are differences in the proteins found in the two types of cells
B. the GI tract does not have epinephrine receptors
C. in cells of the GI tract epinephrine operates via a cytosolic receptor, whereas in cells of the heart epinephrine acts via a plasma membrane receptor
D. the concentration of Ca2+ is lower in the cytosol of GI-tract cells than in the cytosol of heart cells
E. cells of the GI tract lack cAMP

Apoptosis _____. (eText Concept 11.5)

A. typically involves only a single signaling pathway
B. occurs randomly during embryonic development of a nematode
C.. is only triggered by signals from outside the cell
D. is essential for normal development of the nervous system
E. All of the listed responses are correct.

Which of the following statements is/are correct? (eText Concept 11.5)

A. Some apoptotic signals originate from outside a cell.
B. Some apoptotic signals come from the nucleus, when DNA has suffered irreparable damage.
C. Some apoptotic signals come from the endoplasmic reticulum when excessive protein misfolding occurs.
D. Some apoptotic signals come from mitochondria.
E. All of the listed responses are correct.