Key Concepts:
• External signals are converted to responses within the cell.
• Reception: A signaling molecule binds to a receptor protein, causing it to change shape.
• Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell.
• Response: Cells signaling leads to regulation of transportation or cytoplasmic activities.
• Apoptosis integrates multiple cell-signaling pathways.
Terms : Hide Images
| 1783912850 | Adenylyl Cyclase | an enzyme that converts ATP to cyclic AMP in response to an extracellular signal | 0 | |
| 1783912851 | Apoptosis | a type of programmed cell death, which is brought about by activation of enzymes that break down many chemical components in the cell | 1 | |
| 1785899114 | Aster | a radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis | 2 | |
| 1785899115 | Autosome | a chromosome that is not directly involved in determining sex; not a sex chromosome | 3 | |
| 1785899116 | Cyclic AMP (cAMP) | cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells; it is also a regulator of some bacterial operons | 4 | |
| 1785899117 | Diacylglycerol (DAG) | second messenger produced by the cleavage of the phospholipid PIP2 in the plasma membrane | 5 | |
| 1785899118 | Diploid Cell | a cell containing two sets of chromosomes (2n), one set inherited from each parent | 6 | |
| 1785899119 | G Protein | a GTP-binding protein that relays signals from a plasma membrane signal receptor, known as a G protein-coupled receptor, to other signal transduction proteins inside the cell | 7 | |
| 1785899120 | G Protein-Coupled Receptor (GPCR) | a signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein; also called a G protein-linked receptor | 8 | |
| 1785899121 | Hormone | in multicellular organisms, one of many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the organism, changing the target cells' functioning | 9 | |
| 1785899122 | Inositol Trisphosphate (IP3) | a second messenger that functions as an intermediate between certain signaling molecules and a subsequent second messenger, Ca2+, by causing a rise in cytoplasmic Ca2+ concentration | 10 | |
| 1785899123 | Ligand | a molecule that binds specifically to another molecule, usually a larger one | 11 | |
| 1785899124 | Ligand-Gated Ion Channel | a transmembrane protein containing a pore that opens or closes as it changes shape in response to a signaling molecule (ligand), allowing or blocking the flow of specific ions; also called an ionotropic receptor | 12 | |
| 1785899125 | Protein Kinase | an enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein | 13 | |
| 1785899126 | Protein Phosphatase | an enzyme that removes phosphate groups from (dephosphorylates) proteins, often functioning to reverse the effect of a protein kinase | 14 | |
| 1785899127 | Reception | in cellular communication, the first step of a signaling pathway in which a signaling molecule is detected by a receptor molecule on or in the cell | 15 | |
| 1785899128 | Receptor Tyrosine Kinase (RTK) | a receptor protein spanning the plasma membrane, the cytoplasmic (intracellular) part of which can catalyze the transfer of a phosphate group from ATP to a tyrosine on another protein; receptor tyrosine kinases often respond to the binding of a signaling molecule by dimerizing and then phosphorylating a tyrosine on the cytoplasmic portion of the other receptor in the dimer | 16 | |
| 1785899129 | Response | (1) in cellular communication, the change in a specific cellular activity brought about by a transduced signal from outside the cell; (2) in feedback regulation, a physiological activity triggered by a change in a variable | 17 | |
| 1785899130 | Scaffolding Protein | a type of large relay protein to which several other relay proteins are simultaneously attached, increasing the efficiency of signal transduction | 18 | |
| 1785899131 | Second Messenger | a small, nonprotein, water-soluble molecule or ion, such as a calcium ion (Ca2+) or cyclic AMP, that relays a signal to a cell's interior in response to a signaling molecule bound by a signal receptor protein | 19 | |
| 1785899132 | Signal Transduction Pathway | a series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response | 20 | |
| 1812728367 | Evidence that cell signaling evolved early in the history of life comes from __________. 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 cell-signaling mechanisms in organisms that have a very distant common ancestor | the similarity of cell-signaling mechanisms in organisms that have a very distant common ancestor The molecular details of signal transduction in yeast and mammals are strikingly similar, suggesting that early versions of the cell-signaling mechanisms used today evolved well before the first multicellular creatures appeared on Earth. | 21 | |
| 1812728368 | 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 __________. a. neurotransmitter b. transcription factor c. protein kinase d. local regulator e. G protein | local regulator A transmitting cell can secrete molecules of a local regulator, a substance that influences cells in the vicinity. | 22 | |
| 1812728369 | Early work on signal transduction and glycogen metabolism by Sutherland indicated that __________. 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 | the signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated Enzyme activation could proceed only when the plasma membrane was intact. | 23 | |
| 1812728370 | Certain yeast cells secrete a molecule called the α factor. The purpose of this molecule is to __________. 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 cells of the opposite mating type, a yeast cells, 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 | stimulate cells of the opposite mating type, a yeast cells, to grow toward the α cell The α factor molecule is a signal molecule that eventually leads to the fusion of opposite yeast mating types. | 24 | |
| 1812728371 | Cells use different signaling strategies to achieve different goals. In hormonal signaling __________. 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 | specialized cells release hormone molecules into the circulatory system, permitting distant cells to be affected Endocrine cells release molecules into the circulatory system, permitting a rapid distribution of the cells throughout the body. | 25 | |
| 1812728372 | What did Sutherland discover about glycogen metabolism in liver cells? 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 hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell. Epinephrine activates the receptor to carry out the breakdown of glycogen into glucose. | 26 | |
| 1812728373 | 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? 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. | Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus. Nonpolar signal molecules easily enter cells, but only those cells with functional intracellular receptors respond. | 27 | |
| 1812728374 | Different types of cells can respond differently to the same signaling molecule. Which of the following explains this apparent paradox? a. Different types of cells possess different genomes. b. Different types of cells possess different proteins. 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. | Different types of cells possess different proteins. Fundamental differences between cells cause differences in the nature of the cells' response to a signal. This is best explained by the differences in the proteins that the cell makes. | 28 | |
| 1812728375 | Steroid hormones can enter a cell by simple diffusion. Therefore steroids __________. 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 | do not initiate cell signaling by interacting with a receptor in the plasma membrane Steroid hormones, because of their hydrophobic characteristics, readily cross cell membranes and bind to receptors in the cytoplasm, activating the receptor. The active receptor protein then binds to and turns off genes in the nucleus that control the response. Thus, the receptor carries out the complete transduction of the signal. | 29 | |
| 1812728376 | Steroid hormones can enter a cell by simple diffusion. Therefore, steroids do which of the following? a. move up a concentration gradient and are nonpolar b. move up a concentration gradient 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. | None of the listed responses is correct. Simple diffusion must occur down a gradient, and as the molecule moving must pass through the membrane, that molecule must be nonpolar; no membrane protein is required for passive diffusion. | 30 | |
| 1812728377 | A small molecule that specifically binds to a larger molecule is called a(n) __________. a. α protein b. ligand c. protein kinase d. competitive inhibitor e. DAG | ligand A ligand is a small molecule that specifically binds to a larger one. | 31 | |
| 1812728378 | Receptors for signal molecules __________. a. all act 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 | may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus Not all signal receptors are membrane proteins. Some are located in the cytoplasm of target cells. | 32 | |
| 1812728379 | Testosterone does NOT affect all cells of the body because __________. 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 | not all cells have cytoplasmic receptors for testosterone Steroid hormones, such as testosterone, readily enter cells all over the body, but they stimulate a response only in target cells—those with receptor molecules in the cytoplasm. | 33 | |
| 1812728380 | G-protein-coupled receptors __________, whereas receptor tyrosine kinases __________. 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 | are not enzymes ... have enzymatic function GPCRs simply bind ligand and transduce that signal to the inside of the membrane by changing shape—they have no enzymatic activity. Receptor tyrosine kinases are transmembrane proteins that attach phosphates to protein tyrosines. | 34 | |
| 1812728381 | Which of the following is activated when the binding of single molecules causes it to form a dimer? a. ion-channel receptors b. protein phosphatase receptors c. G-protein-coupled receptors d. adenylyl cyclase receptors e. receptor tyrosine kinases | receptor tyrosine kinases Ligand binding causes two tyrosine-kinase receptor polypeptides to associate, forming a dimer. | 35 | |
| 1812728382 | The binding of a signal molecule to a ligand-gated ion channel __________. 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 | affects the membrane potential Ligand-gated ion channels are protein pores in the plasma membrane that open or close in response to a chemical signal, allowing or blocking the flow of specific ions. | 36 | |
| 1812728383 | Nitric oxide is unusual among animal signal molecules in that it __________. 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 | is a gas Chemical messengers with intracellular receptors include the steroid hormones and even the small gaseous molecule nitric oxide. | 37 | |
| 1812728384 | A G protein is active when __________. 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 a protein kinase e. Ca2+ binds to a G-protein-coupled receptor | GTP is bound to it When GDP is bound, the G protein is inactive; when GTP is bound, it is active. | 38 | |
| 1812728385 | 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 __________. a. the inactivation of ligand-gated ion channels b. the inactivation of G-protein-coupled 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 | that the activated G proteins would remain locked in the "on" position, transmitting signal even in the absence of a signaling molecule GTP-bound G proteins remain active until the GTP is converted to GDP. If the GTP cannot be hydrolyzed to GDP, the G protein remains active. | 39 | |
| 1812728386 | What event would activate a G protein? 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 | replacement of GDP with GTP Inactive G proteins are bound to GDP. The activated receptor replaces the GDP with GTP, thereby activating the G protein. | 40 | |
| 1812728387 | 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 could explain uncontrolled division in a cancer cell that has mutated Ras present? 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 | a mutation that means Ras cannot hydrolyze GTP to GDP Such a mutation would mean that Ras would always be turned on, and would thus signal to the cell to divide continuously. Such division could lead to cancer. | 41 | |
| 1812728388 | The cellular response of a signal pathway that terminates at a transcription factor would be __________. 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 | the synthesis of mRNA Transcription factors are proteins that regulate the transcription of DNA into mRNA. | 42 | |
| 1812728389 | Cholera develops when the bacterial toxin __________. 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 | prevents G-protein inactivation, which leads to the continuous production of cAMP The activated G protein continuously stimulates adenylyl cyclase to make cAMP, which causes the intestinal cells to secrete large amounts of water and salts into the intestines. | 43 | |
| 1812728390 | The general name for an enzyme that transfers phosphate groups from ATP to a protein is __________. a. protein dehydrogenase b. protein phosphatase c. protein kinase d. peptidase e. protein cyclase | protein kinase Most protein kinases attach phosphate groups to proteins different from themselves. However, some protein kinases phosphorylate other protein kinases of the same type. | 44 | |
| 1812728391 | ATPgammaS is a form of ATP that CANNOT be hydrolyzed by enzymes. If this compound were introduced to cells so that it replaced the normal ATP present in the cell, which of the following would you predict? 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. | a decrease in phosphorylated proteins in the cell Protein kinases transfer the gamma phosphate from ATP to a target protein. ATPgammaS cannot be hydrolyzed and so cannot be used by protein kinases. | 45 | |
| 1812728392 | Phosphorylation __________. a. always inactivates a protein b. activates G-protein-coupled receptors c. can either activate or inactivate a protein d. is accomplished by protein phosphatases e. always activates a protein | can either activate or inactivate a protein The addition of a phosphate often activates a protein, although in other cases phosphorylation decreases the activity of the protein. | 46 | |
| 1812728393 | The source of phosphate for a phosphorylation cascade is __________. a. cAMP b. ATP c. protein kinase d. GTP e. protein phosphatase | ATP Phosphate groups are transferred from ATP to proteins in a phosphorylation cascade. | 47 | |
| 1812728394 | Second messengers tend to be water-soluble and small. This accounts for their ability to __________. 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 | rapidly move throughout the cell by diffusion Diffusion permits a wide dispersal of the molecules from the site of their entry or production at a membrane. | 48 | |
| 1812728395 | The molecule cAMP usually directly activates __________. a. phosphodiesterase b. receptor tyrosine kinases c. G proteins d. adenylyl cyclase e. protein kinase A | protein kinase A The relay molecule that is activated by cAMP in a signaling cascade is usually protein kinase A, a serine/threonine kinase. | 49 | |
| 1812728396 | A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to __________. 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 | lower activity of protein kinase A Protein kinase A is activated by cAMP and if adenylyl cyclase could not make cAMP, then protein kinase A would not be as active as it should. | 50 | |
| 1812728397 | 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? 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. | The kainate receptor is a ligand-gated ion channel and domoic acid is a ligand. There is more calcium outside the cell and binding of domoic acid would open the channel and allow calcium to move into the cell, down the calcium gradient. | 51 | |
| 1812728398 | Which of the following statements about calcium ions in a typical cell is true? a. In a typical cell, calcium ions are far more abundant in the cytoplasm than in the blood and other extracellular fluid. b. In a typical cell, calcium ions are rapidly transported into the endoplasmic reticulum in response to G-protein-mediated signals. c. In a typical cell, calcium ions are often concentrated within the endoplasmic reticulum. d. In a typical cell, calcium ions are not very widely used as second messengers. e. All of the listed responses are correct. | In a typical cell, calcium ions are often concentrated within the endoplasmic reticulum. Low intracellular concentrations are achieved by transporting calcium across the plasma membrane or into storage sites within the endoplasmic reticulum. | 52 | |
| 1812728399 | During the transduction of a signal, one molecule or ion may be closely associated with the activity of another. Which of the following pairs correctly combines two associated molecules? a. calcium, IP3 b. cAMP, adenylyl cyclase c. cAMP, protein kinase A d. DAG, IP3 e. All of the listed responses are correct. | All of the listed responses are correct. Each of the pairs above is properly associated. | 53 | |
| 1812728400 | A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that cAMP __________ and Ca2+ __________. 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 e. enters the cell via a transmembrane protein channel ... enters the cell by diffusing across the plasma membrane | is synthesized by an enzyme in response to a signal ... is released from intracellular stores Adenylyl cyclase catalyzes the conversion of ATP to cAMP. Calcium released from the endoplasmic reticulum increases the cytosolic concentration of calcium and causes many responses in animal cells, including muscle-cell contraction. | 54 | |
| 1812728401 | IP3 (inositol trisphosphate) is produced as a result of __________. a. protein kinase A activation b. Ca2+ c. the cleavage of a specific phospholipid in the plasma membrane d. DAG e. adenylyl cyclase | the cleavage of a specific phospholipid in the plasma membrane Phospholipase C cleaves a special membrane phospholipid, PIP2, producing diacylglycerol and inositol trisphosphate. | 55 | |
| 1812728402 | IP3 (inositol trisphosphate) acts by __________. a. activating cAMP b. phosphorylating signal receptors c. opening Ca2+ channels d. activating PIP2 e. activating DAG | opening Ca2+ channels IP3 binds to ligand-gated ion channels to stimulate the release of calcium from the endoplasmic reticulum. | 56 | |
| 1812728403 | 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? a. glycogen b. cyclic AMP c. tRNA d. epinephrine e. glucose | cyclic AMP The first messenger, the hormone, causes a membrane enzyme to synthesize cAMP, which transmits the signal to the cytoplasm. | 57 | |
| 1812728404 | In the inherited disorder Wiskott-Aldrich syndrome, __________. 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 | a multifunctional relay protein involved with the proliferation of immune cells is defective The defective protein is thought to represent an important intersection point for a complex transduction network. | 58 | |
| 1812728405 | In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, __________. 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. glycogen synthesis is stimulated | the signal is amplified The signal-transduction pathway from epinephrine to the breakdown of glycogen amplifies the hormonal signal because the receptor protein can activate many molecules of G protein. | 59 | |
| 1812728406 | Cells of the gastrointestinal (GI) tract and cells of the heart respond differently to epinephrine because __________. a. there are differences in the proteins found in the two types of cells b. the GI tract does not have receptor tyrosine kinases 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 ATP | there are differences in the proteins found in the two types of cells The specific proteins a cell possesses determine which signal molecules it responds to and the nature of that response. | 60 | |
| 1812728407 | Which of the following statements about apoptosis is true? a. Apoptosis typically involves only a single signaling pathway. b. Apoptosis occurs randomly during embryonic development of a nematode. c. Apoptosis is triggered only by signals from outside the cell. d. Apoptosis is essential for normal development of the nervous system. e. All of the listed responses are correct. | Apoptosis is essential for normal development of the nervous system. Many neurons undergo apoptosis as part of normal embryonic development. | 61 | |
| 1812728408 | Which of the following statement is correct? 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. | All of the listed responses are correct. All of the listed responses are correct. | 62 | |
| 1812728409 | 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. intracellular receptor b. G protein-coupled receptor c. receptor tyrosine kinase d. phosphorylated receptor tyrosine kinase dimer e. ligand-gated ion channel | ligand-gated ion channel | 63 | |
| 1812728410 | The activation of receptor tyrosine kinases is characterized by a. a phosphorylation cascade. b. dimerization and phosphorylation. c. dimerization and IP3 binding. d. channel protein shape change. e. GTP hydrolysis. | dimerization and phosphorylation. | 64 | |
| 1812728411 | Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because a. only target cells retain the appropriate DNA segments. b. only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on. c. only target cells have enzymes that break down aldosterone. d. intracellular receptors are present only in target cells. e. only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor. | intracellular receptors are present only in target cells. | 65 | |
| 1812728412 | Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger. a. cAMP b. adenylyl cyclase c. G protein d. G protein-coupled receptor e. GTP | cAMP | 66 | |
| 1812728413 | Apoptosis involves all but which of the following? a. cell-signaling pathways b. lysis of the cell c. fragmentation of the DNA d. digestion of cellular contents by scavenger cells e. activation of cellular enzymes | lysis of the cell | 67 | |
| 1812728414 | 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. Receptor studies indicated that epinephrine was a ligand. c. Enzymatic activity was proportional to the amount of calcium added to a cell-free extract. d. Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined. e. Epinephrine was known to have different effects on different types of cells. | Glycogen breakdown was observed only when epinephrine was administered to intact cells. | 68 | |
| 1812728415 | Protein phosphorylation is commonly involved with all of the following except a. activation of protein kinase molecules. b. activation of receptor tyrosine kinases. c. activation of G protein-coupled receptors. d. regulation of transcription by extracellular signaling molecules. e. enzyme activation. | activation of G protein-coupled receptors. | 69 |
