5) Hormones are chemical substances produced in one organ that are released into the bloodstream and affect the function of a target organ. For the target organ to respond to a particular hormone, it must _____.
A) modify its plasma membrane to alter the hormone entering the cytoplasm

B) be from the same cell type as the organ that produced the hormone

C) experience an imbalance that disrupts its normal function
D) have receptors that recognize and bind the hormone molecule

Answer: D

6) In which of the following ways do plant hormones differ from hormones in animals?

A) Plant hormones most often travel in air as a gas.
B) Animal hormones are only local regulators.
C) Plant hormones are typically released into the soil.

D) Animal hormones are primarily for mating and embryonic development.

Answer: A

7) 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) relay molecule
B) transducer

C) signal molecule
D) response molecule

Answer: C

10) Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?
A) Receptor studies indicated that epinephrine was a ligand.
B) Glycogen breakdown was observed only when epinephrine was administered to intact cells.

C) Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined.

D) Epinephrine was known to have different effects on different types of cells.

Answer: B

11) A G-protein receptor with GTP bound to it _____.
A) is in its active state
B) signals a protein to maintain its shape and conformation

C) will use cGMP as a second messenger
D) directly affects gene expression

Answer: A

12) Testosterone functions inside a cell by _____.
A) acting as a signal receptor that activates tyrosine kinases
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) coordinating a phosphorylation cascade that increases spermatogenesis

Answer: B

13) 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) collagens
C) actins
D) fibronectins

Answer: A

14) One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?
A) G protein-coupled receptors
B) ligand-gated ion channels

C) steroid receptors
D) receptor tyrosine kinases

Answer: D

15) A drug designed to inhibit the response of cells to testosterone would most likely result in _____.
A) lower cytoplasmic levels of cAMP
B) a decrease in transcriptional activity of certain genes

C) an increase in cytosolic calcium concentration

D) a decrease in G protein activity

Answer: B

A major group of G protein-coupled receptors contains seven transmembrane α helices. 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 face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.

16) Where would you expect to find the carboxyl end?

A) at the exterior surface
B) at the cytosol surface
C) connected with the loop at H5 and H6

D) between the membrane layers

Answer: B

A major group of G protein-coupled receptors contains seven transmembrane α helices. 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 face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.

17) The coupled G protein most likely interacts with this receptor _____.

A) at the NH3 end
B) at the COO– end
C) along the exterior margin

D) at the loop between H5 and H6

Answer: D

A major group of G protein-coupled receptors contains seven transmembrane α helices. 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 face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.

18) 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) receptor tyrosine kinase
B) G protein-coupled receptor

C) ligand-gated ion channel
D) intracellular receptor

Answer: C

19) Lipid-soluble signaling 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) only target cells possess the cytosolic enzymes that transduce the testosterone
D) only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor

Answer: B

20) 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 and inactivate the G protein on the cytoplasmic side of the plasma membrane.

B) It would be able to carry out reception and transduction but would not be able to respond to a signal.
C) It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.

D) It would employ a transduction pathway directly from an external messenger.

Answer: A

21) Which of the following 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 nuclear membrane.

Answer: B

22) Particular receptor tyrosine kinases (RTKs) that promote excessive cell division are found at high levels on various cancer cells. A protein, Herceptin, has been found to bind to an RTK known as HER2. HER2 is sometimes excessive in cancer cells. This information can now be utilized in breast cancer treatment if which of the following is true?

A) if HER2, administered by injection, causes cell division

B) if the patient's cancer cells have excessive levels of HER2

C) if the patient's genome codes for the HER2 receptor

D) if the patient has RTKs only in cancer cells

Answer: B

23) Which of the following would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins?
A) G protein-coupled receptor binding
B) ligand-gated ion channel signaling

C) adenylyl cyclase activity
D) receptor tyrosine kinase activity

Answer: D

24) Which of the following is characteristic of a steroid hormone action?

A) protein phosphorylation
B) cell-surface receptor binding
C) internal receptor binding

D) second messenger activation

Answer: C

25) The receptors for steroid hormones are located inside the cell instead of on the membrane surface like most other signal receptors. This is not a problem for steroids because _____.
A) the receptors can be readily stimulated to exit and relocate on the membrane surface
B) steroids do not directly affect cells but instead alter the chemistry of blood plasma

C) steroid hormones are lipid soluble, so they can readily diffuse through the lipid bilayer of the cell membrane
D) steroids must first bond to a steroid activator, forming a complex that then binds to the cell surface

Answer: C

26) Not all intercellular signals require transduction. Which one of the following signals would be processed without transduction?
A) a lipid-soluble signal
B) a signal that is weakly bound to a nucleotide

C) a signal that binds to a receptor in the cell membrane

D) a signal that binds to the ECM

Answer: A

27) What does it mean to say that a signal is transduced?
A) The signal enters the cell directly and binds to a receptor inside.
B) The physical form of the signal changes from one form to another.
C) The signal is amplified, such than even a single molecule evokes a large response.

D) The signal triggers a sequence of phosphorylation events inside the cell.

Answer: B

28) Protein phosphorylation is commonly involved with all of the following EXCEPT _____.

A) regulation of transcription by extracellular signaling molecules
B) enzyme activation
C) activation of G protein-coupled receptors

D) activation of protein kinase molecules

Answer: C

29) In general, a signal transmitted via phosphorylation of a series of proteins _____.

A) results in a conformational change to each protein
B) requires binding of a hormone to an intracellular receptor
C) activates a transcription event

D) generates ATP in the process of signal transduction

Answer: A

30) Which of the following is the best explanation for the inability of a specific 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 cytosol

D) low levels of protein kinase in the cell

Answer: C

31) The toxin of Vibrio cholerae causes profuse diarrhea because it _____.

A) modifies a G protein involved in regulating salt and water secretion
B) binds with adenylyl cyclase and triggers the formation of cAMP
C) signals IP3 to act as a second messenger for the release of calcium

D) modifies calmodulin and activates a cascade of protein kinases

Answer: A

32) Which of the following would most likely be an immediate result of a growth factor binding to its receptor?
A) protein kinase activity
B) adenylyl cyclase activity

C) protein phosphatase activity
D) phosphorylase activity

Answer: A

33) Adenylyl cyclase has the opposite effect of which of the following?

A) protein kinase
B) protein phosphatase
C) phosphodiesterase

D) phosphorylase

Answer: C

34) 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) cAMP

C) adenylyl cyclase
D) activated G proteins

Answer: B

35) An inhibitor of which of the following 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

Answer: C

36) Which of the following statements is true of signal molecules?
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.

Answer: D

37) Which of the following is a correct association?
A) kinase activity and the addition of a tyrosine
B) phosphodiesterase activity and the removal of phosphate groups

C) GTPase activity and hydrolysis of GTP to GDP
D) adenylyl cyclase activity and the conversion of cAMP to AMP

Answer: C

38) Protein kinase is an enzyme that _____.
A) functions as a second messenger molecule
B) serves as a receptor for various signal molecules
C) activates or inactivates other proteins by adding a phosphate group to them

D) produces second messenger molecules

Answer: C

39) Viagra causes dilation of blood vessels and increased blood flow to the penis, facilitating erection. Viagra acts by inhibiting _____.
A) the hydrolysis of cGMP to GMP
B) the hydrolysis of GTP to GDP

C) the dephosphorylation of cGMP
D) the removal of GMP from the cell

Answer: A

40) Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction?
A) tyrosines
B) glycine and histidine

C) serine and threonine
D) glycine and glutamic acid

Answer: C

41) In signal transduction, phosphatases _____.
A) move the phosphate group of the transduction pathway to the next molecule of a series

B) prevent a protein kinase from being reused when there is another extracellular signal

C) amplify the second messengers such as cAMP
D) inactivate protein kinases and turn off the signal transduction

Answer: D

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

C) to block G protein activity in liver cells

D) that increases phosphorylase activity

Answer: C

43) If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound _____.
A) that mimics epinephrine and can bind to the epinephrine receptor
B) that stimulates cAMP production in liver cells

C) to stimulate G protein activity in liver cells

D) that increases phosphodiesterase activity

Answer: D

44) Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. The second messenger in this pathway is _____.
A) cAMP
B) G protein

C) adenylyl cyclase
D) G protein-coupled receptor

Answer: A

45) Sutherland discovered that the signaling molecule epinephrine _____.
A) brings about a decrease in levels of cAMP as a result of bypassing the plasma membrane

B) causes lower blood glucose by binding to liver cells
C) interacts directly with glycogen phosphorylase
D) elevates cytosolic concentrations of cyclic AMP

Answer: D

46) Which of the following is true during a typical cAMP-type signal transduction event?
A) The second messenger is the last part of the system to be activated.
B) The hormone activates the second messenger by directly binding to it.
C) The second messenger amplifies the hormonal response by attracting more hormones to the cell being affected.

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

Answer: D

47) 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) 1, 2, 3, 4, 5
B) 3, 1, 2, 4, 5
C) 3, 1, 5, 2, 4
D) 1, 2, 5, 3, 4

Answer: C

48) Transcription factors _____.
A) regulate the synthesis of DNA in response to a signal

B) transcribe ATP into cAMP
C) control gene expression
D) regulate the synthesis of lipids in the cytoplasm

Answer: C

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

Answer: D

50) Scaffolding proteins are _____.
A) microtubular protein 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 their complexing
D) proteins that can reach into the nucleus of a cell to affect transcription

Answer: B

51) Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because they _____.
A) are species specific
B) always lead to the same cellular response

C) amplify the original signal many times
D) counter the harmful effects of phosphatases

Answer: C

52) GTPase activity is important in the regulation of signal transduction because it _____.

A) increases the available concentration of phosphate
B) decreases the amount of G protein in the membrane
C) hydrolyzes GTP to GDP, thus shutting down the pathway

D) converts cGMP to GTP

Answer: C

53) Why has C. elegans proven to be a useful model for understanding apoptosis?
A) The animal does not naturally use apoptosis, but can be induced to do so in the laboratory.

B) The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.
C) This plant has a long-studied aging mechanism that has made understanding its death just a last stage.
D) While the organism ages, its cells die progressively until the whole organism is dead.

Answer: B

54) Which of the following 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 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.
D) The cell's nucleus and organelles are lysed, then the cell enlarges and bursts.

Answer: C

55) If an adult person has a faulty version of the human analog to ced-4 of the nematode, which of the following is most likely to result?
A) activation of a developmental pathway found in the worm but not in humans
B) a form of cancer in which there is insufficient apoptosis

C) formation of molecular pores in the mitochondrial outer membrane

D) excess skin loss

Answer: B

56) Why is apoptosis potentially threatening to the healthy "neighbors" of a dying cell?
A) Cell death would usually spread from one cell to the next via paracrine signals.
B) Lysosomal enzymes exiting the dying cell would damage surrounding cells.
C) Bits of membrane from the dying cell could merge with neighboring cells and bring in foreign receptors.

D) Neighboring cells would activate immunological responses.

Answer: B

57) 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 remains inactive until it is signaled by ced-3 and other caspases.

C) Ced-9 cleaves to produce ced-3 and ced-4.
D) Ced-9 prevents blebbing by its action on the cell membrane.

Answer: A

58) 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) Hormone concentrations decrease.
C) cAMP levels change very frequently.
D) Enzymatic activity declines.

Answer: A

59) Apoptosis involves all but which of the following?

A) fragmentation of the DNA
B) activation of cellular enzymes
C) lysis of the cell

D) digestion of cellular contents by scavenger cells

Answer: C

60) An unlabeled signaling diagram for steroid hormones: Fig. 11.8 p. 213, Campbell 8e.

A steroid hormone, like estrogen, passes through the plasma membrane and binds to an intracellular protein as shown in the diagram below. This activates a signal-transduction pathway which results in an increased production of a specific protein.

Which of the following statements would explain what would occur as a result of the signal pathway represented by the diagram?
A) Transfer RNA (t-RNA) would accumulate in high levels because it is not required for protein synthesis.
B) Ribosomal RNA (r-RNA) levels would increase because ribosomes are specific for the messenger RNA (m-RNA) with which they bind during transcription of the polypeptide.
C) DNA levels would increase in the nucleus as a result of the binding of the hormone-receptor complex with the DNA.
D) Messenger RNA (m-RNA) levels would increase in order to be translated into the protein required by the cell.

Answer: D

61) Which of the following poses the best evidence that cell-signaling pathways evolved early in the history of life?
A) Cell-signaling pathways are seen in "primitive" cells such as bacteria and yeast.
B) Bacteria and yeast cells signal each other in a process called quorum sensing.

C) Signal transduction molecules identified in distantly related organisms are similar.

D) Most signals in all types of cells are received by cell surface receptors.

Answer: C

62) 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) Apoptosis is regulated by cell surface receptors that signal when a cell has reached its density-dependent limits.

B) During apoptosis, dying cells leak out their contents including digestive enzymes that also destroy healthy cells.
C) During apoptosis, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components of a cell.

D) Each cell organelle has protein signals that initiate the breakdown of the organelle's components which leads to cell death.

Answer: C