ch 11 practice problems

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60) The activation of receptor tyrosine kinases is always characterized by A) dimerization and phosphorylation. B) IP3 binding. C) a phosphorylation cascade. D) GTP hydrolysis. E) channel protein conformational change.

64) Amplification of a chemical signal occurs when A) a receptor in the plasma membrane activates several G-protein molecules while a signal molecule is bound to it. B) a cAMP molecule activates one protein kinase molecule before being converted to AMP. C) phosphorylase and phosphatase activities are balanced. D) receptor tyrosine kinases dimerize upon ligand binding. E) Both A and D occur.

67) Consider this pathway: epinephrine → G-protein-linked receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger. A) cAMP B) G protein C) GTP D) adenylyl cyclase E) G-protein-linked receptor

2) In the yeast signal transduction pathway, after both types of mating cells have released the mating factors and the factors have bound to specific receptors on the correct cells, A) binding induces changes in the cells that lead to cell fusion. B) the cells then produce the a factor and the α factor. C) one cell nucleus binds the mating factors and produces a new nucleus in the opposite cell. D) the cell membranes fall apart, releasing the mating factors that lead to new yeast cells. E) a growth factor is secreted that stimulates mitosis in both cells.

A Topic: Concept 11.1 Skill: Comprehension

11) The signal transduction pathway in animal cells that use epinephrine A) activates the breakdown of glycogen in liver and skeletal muscle cells. B) is a classic example of synaptic signaling. C) operates independently of hormone receptors on target cells. D) A and B only E) A, B, and C

A Topic: Concept 11.1 Skill: Knowledge

5) Paracrine signaling A) involves secreting cells acting on nearby target cells by discharging a local regulator into the extracellular fluid. B) requires nerve cells to release a neurotransmitter into the synapse. C) occurs only in paracrine yeast cells. D) has been found in plants but not animals. E) involves mating factors attaching to target cells and causing production of new paracrine cells.

A Topic: Concept 11.1 Skill: Knowledge

14) Of the following, a receptor protein in a membrane that recognizes a chemical signal is most similar to A) the active site of an enzyme in the cytoplasm that binds to a specific substrate. B) RNA specifying the amino acids in a polypeptide. C) a particular metabolic pathway operating within a specific organelle. D) an enzyme with an optimum pH and temperature for activity. E) genes making up a chromosome.

A Topic: Concept 11.2 Skill: Comprehension

17) What would be true for the signaling system in an animal cell that lacks the ability to produce GTP? A) It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. B) It could activate only the epinephrine system. C) It would be able to carry out reception and transduction, but would not be able to respond to a signal. D) Only A and C are true. E) A, B, and C are true.

A Topic: Concept 11.2 Skill: Comprehension

27) In general, a signal transmitted via phosphorylation of a series of proteins A) brings a conformational change to each protein. B) requires binding of a hormone to a cytosol receptor. C) cannot occur in yeasts because they lack protein phosphatases. D) requires phosphorylase activity. E) allows target cells to change their shape and therefore their activity.

A Topic: Concept 11.3 Skill: Comprehension

31) A plant deficient in calcium could experience several problems, including A) poor response to signals of stress, drought, or cold. B) decreased response to epinephrine. C) overactive cyclic AMP responses. D) B and C only E) A, B, and C

A Topic: Concept 11.3 Skill: Comprehension

32) An animal deficient in adenylyl cyclase A) would not respond properly to epinephrine. B) could not convert GTP to ATP. C) would lack plasma membrane bound receptors. D) A and B only E) A, B, and C

A Topic: Concept 11.3 Skill: Comprehension

41) Which of the following most likely would be an immediate result of growth factor binding to its receptor? A) protein kinase activity B) adenylyl cyclase activity C) GTPase activity D) protein phosphatase activity E) phosphorylase activity

A Topic: Concept 11.3 Skill: Comprehension

37) The toxin of Vibrio cholerae causes profuse diarrhea because it A) modifies a G protein involved in regulating salt and water secretion. B) decreases the cytosolic concentration of calcium ions, making the cells hypotonic to the intestinal cells. C) binds with adenylyl cyclase and triggers the formation of cAMP. D) signals inositol trisphosphate to become a second messenger for the release of calcium. E) modifies calmodulin and activates a cascade of protein kinases.

A Topic: Concept 11.3 Skill: Knowledge

56) The cleavage of glycogen by glycogen phosphorylase releases ________. A) glucose-1-phosphate B) cellulose C) galactose-1-phosphate D) fructose-1-phosphate E) nothing; glycogen phosphorylase cannot cleave glycogen

A Topic: Web/CD Activity: Cellular Responses

65) Lipid-soluble signal molecules, such as testosterone, cross the membranes of all cells but affect only target cells because A) only target cells retain the appropriate DNA segments. B) intracellular receptors are present only in target cells. C) most cells lack the Y chromosome required. D) only target cells possess the cytosolic enzymes that transduce the testosterone. E) only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor.

6) Which of the following is true of synaptic signaling and hormonal signaling? A) Hormonal signaling occurs in animals only. B) Hormonal signaling is important between cells that are at greater distances apart than in synaptic signaling. C) Both act on target cells by a G-protein-signaling pathway. D) Only A and B are true. E) A , B, and C are true.

B Topic: Concept 11.1 Skill: Comprehension

1) In yeast (Saccharomyces cerevisiae), the two sexes are called A) S plus and S minus. B) a and α. C) a and b. D) b and β. E) male and female.

B Topic: Concept 11.1 Skill: Knowledge

3) Which of the following is true of the mating signal transduction pathway in yeast? A) The pathway carries an electrical signal between mating cell types. B) Mating type a secretes a signal called a factor. C) The molecular details of the pathway in yeast and in animals are very different. D) Scientists think the pathway evolved long after multicellular creatures appeared on Earth. E) The signal reception, transduction, and response occur in the nucleus.

B Topic: Concept 11.1 Skill: Knowledge

8) From the perspective of the cell receiving the message, the three stages of cell signaling are A) the paracrine, local, and synaptic stages. B) signal reception, signal transduction, and cellular response. C) signal reception, nucleus disintegration, and new cell generation. D) the alpha, beta, and gamma stages. E) signal reception, cellular response, and cell division.

B Topic: Concept 11.1 Skill: Knowledge

9) The process of transduction usually begins A) when the chemical signal is released from the alpha cell. B) when the signal molecule changes the receptor protein in some way. C) after the target cell divides. D) after the third stage of cell signaling is completed. E) when the hormone is released from the gland into the blood.

B Topic: Concept 11.1 Skill: Knowledge

23) Testosterone functions inside a cell by A) acting as a signal receptor that activates ion-channel proteins. B) binding with a receptor protein that enters the nucleus and activates specific genes. C) acting as a steroid signal receptor that activates ion-channel proteins. D) becoming a second messenger that inhibits adenylyl cyclase. E) coordinating a phosphorylation cascade that increases glycogen metabolism.

B Topic: Concept 11.2 Skill: Comprehension

12) A small molecule that specifically binds to another molecule, usually a larger one A) is called a signal transducer. B) is called a ligand. C) is called a polymer. D) seldom is involved in hormonal signaling. E) usually terminates a signal reception.

B Topic: Concept 11.2 Skill: Knowledge

20) Membrane receptors that attach phosphates to specific animo acids in proteins are A) not found in humans. B) called receptor tyrosine-kinases. C) a class of GTP G-protein signal receptors. D) associated with several bacterial diseases in humans. E) important in yeast mating factors that contain amino acids.

B Topic: Concept 11.2 Skill: Knowledge

49) Which of the following is an incorrect association? A) kinase activity and the addition of a phosphate group B) phosphodiesterase activity and the removal of phosphate groups C) GTPase activity and hydrolysis of GTP to GDP D) phosphorylase activity and the catabolism of glycogen E) adenylyl cyclase activity and the conversion of AMP to cAMP

B Topic: Concept 11.3 Skill: Application

28) Which of the following is (are) true regarding the activity of a protein regulated by phosphorylation? A) It depends mostly on the concentration of inorganic phosphate inside the cell. B) It depends on the balance in the cell between active kinase and active phosphatase molecules. C) It is dependent on the site of attachment of the protein to the plasma membrane. D) Only A and B are true. E) A, B, and C are true.

B Topic: Concept 11.3 Skill: Comprehension

48) Which of the following statements is incorrect? A) When signal molecules bind to receptor tyrosine kinases, the receptors phosphorylate themselves. B) In response to some G-protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3and calcium. C) In most cases, signal molecules interact with the cell at the plasma membrane and never actually enter the cell. D) Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in adenylyl cyclase activity in the absence of an appropriate signal molecule. E) Protein kinase A activation is one possible result of signal molecules binding to G-protein-linked receptors.

B Topic: Concept 11.3 Skill: Comprehension

33) Which of the following is not considered a second messenger? A) cAMP B) GTP C) calcium ions D) diacylglycerol (DAG) E) inositol trisphosphate (IP3)

B Topic: Concept 11.3 Skill: Knowledge

61) Which of the following provides the best evidence that cell-signaling pathways evolved early in the history of life? A) They are seen in "primitive" cells such as yeast. B) Yeast cells signal each other for mating. C) Signal transduction molecules found in distantly related organisms are similar. D) Signals can be sent long distances by cells. E) Most signals are received by cell surface receptors.

62) 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) Receptor studies indicated that epinephrine was a ligand. C) Glycogen breakdown was observed only when epinephrine was administered to intact cells. 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.

63) Protein phosphorylation is commonly involved with all of the following except A) regulation of transcription by extracellular signal molecules. B) enzyme activation. C) activation of G-protein-linked receptors. D) activation of receptor tyrosine kinases. E) activation of protein kinase molecules.

66) Signal transduction pathways benefit cells for all of the following reasons except A) they help cells respond to signal molecules that are too large or too polar to cross the plasma membrane. B) they enable different cells to respond appropriately to the same signal. C) they help cells use up phosphate generated by ATP breakdown. D) they can amplify a signal. E) variations in the signal transduction pathways can enhance response specificity.

Self-Quiz Questions 58) Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because A) they are species specific. B) they always lead to the same cellular response. C) they amplify the original signal manyfold. D) they counter the harmful effects of phosphatases. E) the number of molecules used is small and fixed.

7) The old saying "one rotten apple spoils the whole barrel" is due to chemical signaling in plants via A) an increased uptake of carbon dioxide during respiration in target cells. B) a local regulator for apple development. C) release of ethylene gas, a plant hormone for ripening. D) an a/α cell signal system in the rotten apple. E) a signal transduction pathway involving glycogen phosphorylase.

C Topic: Concept 11.1 Skill: Comprehension

10) When a cell releases a signal molecule into the environment and a number of cells in the immediate vicinity respond, this type of signaling is A) typical of hormones. B) autocrine signaling. C) paracrine signaling. D) endocrine signaling. E) synaptic signaling.

C Topic: Concept 11.1 Skill: Knowledge

18) G proteins and G-protein-linked receptors A) are found only in animal cells. B) are found only in bacterial cells. C) are thought to have evolved very early, because of their similar structure and function in a wide variety of modern organisms whose common ancestors diverged billions of years ago. D) probably evolved from an adaptation of the citric acid cycle. E) are not widespread in nature and were unimportant in the evolution of eukaryotes.

C Topic: Concept 11.2 Skill: Knowledge

44) Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of A) phosphorylated proteins. B) GTP. C) cAMP. D) adenylyl cyclase. E) activated G proteins.

C Topic: Concept 11.3 Skill: Application

34) Which of the following is the best explanation for the inability of an animal cell to reduce the Ca2+concentration in its cytosol compared with the extracellular fluid? A) blockage of the synaptic signal B) loss of transcription factors C) insufficient ATP levels in the cytoplasm D) low oxygen concentration around the cell E) low levels of protein kinase in the cell

C Topic: Concept 11.3 Skill: Comprehension

36) Which of the following is not true of cell communication systems? A) Cell signaling was an early event in the evolution of life. B) Communicating cells may be far apart or close together. C) Most signal receptors are bound to the outer membrane of the nuclear envelope. D) Protein phosphorylation is a major mechanism of signal transduction. E) In response to a signal, the cell may alter activities by changes in cytosol activity or in transcription of RNA.

C Topic: Concept 11.3 Skill: Comprehension

35) The general name for an enzyme that transfers phosphate groups from ATP to a protein is A) phosphorylase. B) phosphatase. C) protein kinase. D) ATPase. E) protease.

C Topic: Concept 11.3 Skill: Knowledge

38) Which of the following is not part of the phosphorylation cascade model? A) A signal molecule binds to a membrane receptor protein. B) Protein kinase is activated. C) GTP donates a phosphate group to an inactive protein kinase. D) A specific protein is activated via phosphorylation. E) A cellular response is initiated.

C Topic: Concept 11.3 Skill: Knowledge

43) Adenylyl cyclase has the opposite effect of which of the following? A) protein kinase B) protein phosphatase C) phosphodiesterase D) phosphorylase E) GTPase

C Topic: Concept 11.3 Skill: Knowledge

50) A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following? A) lower cytoplasmic levels of cAMP B) an increase in receptor tyrosine kinase activity C) a decrease in transcriptional activity of certain genes D) an increase in cytosolic calcium concentration E) a decrease in G-protein activity

C Topic: Concept 11.4 Skill: Application

59) Binding of a signal molecule to which type of receptor leads directly to a change in the distribution of anions and/or cations on opposite sides of the membrane? A) receptor tyrosine kinase B) G-protein-linked receptor C) phosphorylated receptor tyrosine kinase dimer D) ligand-gated ion channel E) intracellular receptor

4) What could happen to the target cells in an animal that lack receptors for local regulators? A) They could compensate by receiving nutrients via an a factor. B) They could develop normally in response to neurotransmitters instead. C) They could divide but never reach full size. D) They would not be able to multiply in response to growth factors from nearby cells. E) Hormones would not be able to interact with target cells.

D Topic: Concept 11.1 Skill: Comprehension

15) Most signal molecules A) bind to specific sites on receptor proteins in a membrane. B) are water-soluble. C) are able to pass through the plasma membrane by active transport. D) A and B only E) A, B, and C

D Topic: Concept 11.2 Skill: Comprehension

19) The ability of a single ligand bound to a receptor protein to trigger several pathways is A) characteristic of the synaptic signal system. B) unique to the yeast mating system. C) rare in animals, but common in bacteria. D) a key difference between the tyrosine-kinase and G-protein-linked receptor systems. E) common to all plasma membrane receptor proteins.