Chapter 11 Exam Prep
The receptors for a group of signaling molecules known as growth factors are often A) ligand-gated ion channels. B) G protein-coupled receptors. C) cyclic AMP. D) receptor tyrosine kinases. E) neurotransmitters.
Answer: D
Since steroid receptors are located intracellularly, which of the following is true? A) The receptor molecules are themselves lipids or glycolipids. B) The steroid/receptor complex can cross the nuclear membrane. C) The unbound steroid receptors are quickly recycled by lysosomes. D) The concentration of steroid receptors must be relatively high in most cells. E) The receptor molecules are free to move in and out of most organelles.
Answer: B
In an experiment to track the movement of growth factor molecules from secretion to the point of receptor binding in a particular species of mammal, a student found a 20-fold reduction in mm traveled when in the presence of an adrenal hormone. This is in part attributable to which of the following? A) The growth factor is a paracrine signal. B) The growth factor depends on osmosis. C) The mammal only carries growth factor through the lymph. D) The growth factor is an exocrine signal. E) The growth factor is an endocrine signal.
Answer: A
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.
Answer: A
Of the following, a receptor protein in a membrane that recognizes a chemical signal is most similar to A) the active site of an allosteric enzyme that binds to a specific substrate. B) tRNA specifying which amino acids are in a polypeptide. C) a metabolic pathway operating within a specific organelle. D) an enzyme having an optimum pH and temperature for activity. E) an antibody in the immune system.
Answer: A
One inhibitor of cGMP is Viagra. It provides a signal that leads to dilation of blood vessels and increase of blood in the penis, facilitating erection. Since cGMP is inhibited, the signal is prolonged. The original signal that is now inhibited would have A) hydrolyzed cGMP to GMP. B) hydrolyzed GTP to GDP. C) phosphorylated GDP. D) dephosphorylated cGMP. E) removed GMP from the cell.
Answer: A
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. C) binds with adenylyl cyclase and triggers the formation of cAMP. D) signals IP3 to act as a second messenger for the release of calcium. E) modifies calmodulin and activates a cascade of protein kinases.
Answer: A
Using the yeast signal transduction pathways, both types of mating cells release the mating factors. These factors bind to specific receptors on the correct cells, A) which induce changes in the cells that lead to cell fusion. B) which produce more of the a factor in a positive feedback. C) then one cell nucleus binds the mating factors and produces a new nucleus in the opposite cell. D) stimulating cell membrane disintegration, releasing the mating factors that lead to new yeast cells. E) which in turn releases a growth factor that stimulates mitosis in both cells.
Answer: A
What explains the increased concentration of Ca⁺⁺ in the ER? A) Calcium ions are actively imported from the cytoplasm into the ER. B) Calcium concentration is kept low in the cytoplasm because of its high usage level. C) Calcium cannot enter the plasma membrane through ion channels. D) Calcium levels in the blood or other body fluids are extremely low. E) The Ca ions are recycled from other molecules in the ER.
Answer: A
Which of the following is a likely explanation of why natural selection favored the evolution of signals for sexual reproduction? A) Even in the simplest organisms, sexual reproduction required several coordinated responses by cells. B) Multicellular eukaryotes required signals that were responded to by multiple organ systems. C) Cells of several kinds of mating types needed to sort themselves to allow self-recognition. D) Rooted plants required chemical diffusible signals that could travel throughout the organism. E) Hormones required a mechanism for introducing changes in their target tissues.
Answer: A
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 cytoplasm D) low oxygen concentration around the cell E) low levels of protein kinase in the cell
Answer: A
Which of the following is 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) It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. E) It would employ a transduction pathway directly from an external messenger.
Answer: A
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
Answer: A
In which of the following ways could signal transduction most probably be explored in research to treat cancer? A) removal of serine/threonine phosphate acceptors from transduction pathways in colon pre-cancerous growths B) alteration of protein kinases in cell cycle regulation in order to slow cancer growth C) increase in calcium ion uptake into the cytoplasm in order to modulate the effects of environmental carcinogens D) expansion of the role of transduction inhibitors in the cells before they give rise to cancer E) increase in the concentration of phosphodiesterases in order to produce more AMP
Answer: B
In which of the following ways do plant hormones differ from hormones in animals? A) Plant hormones interact primarily with intracellular receptors. B) Plant hormones may travel in air or through vascular systems. C) Animal hormones are found in much greater concentration. D) Plant hormones are synthesized from two or more distinct molecules. E) Animal hormones are primarily for mating and embryonic development.
Answer: B
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) becoming a second messenger that inhibits adenylyl cyclase. E) coordinating a phosphorylation cascade that increases spermatogenesis.
Answer: B
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
Answer: C
Adenylyl cyclase has the opposite effect of which of the following? A) protein kinase B) protein phosphatase C) phosphodiesterase D) phosphorylase E) GTPase
Answer: C
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.
Answer: C
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. E) that keeps sugar molecules from crossing the plasma membrane of liver cells.
Answer: C
In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function? A) formation of mating complexes B) secretion of apoptotic signals C) aggregation of bacteria that can cause cavities D) secretion of substances that inhibit foreign bacteria E) digestion of unwanted parasite populations
Answer: C
Receptor tyrosine kinases (RTKs) are found at high levels on various cancer cells. A protein, Herceptin, has been found to bind to an RTK known as HER2. This information can now be utilized in breast cancer treatment if which of the following is true? A) If Herceptin is found in the breast lymph nodes of the patient. B) If HER2, administered by injection, is in sufficient concentration. C) If the patient's cancer cells have detectable HER2. D) If the patient's genome codes for the HER2 receptor. E) If the patient's genome codes for the manufacture of Herceptin.
Answer: C
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 E) Any of the 20 amino acids are equally phosphorylated.
Answer: C
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) phosphorylase activity and the catabolism of glucose E) adenylyl cyclase activity and the conversion of cAMP to AMP
Answer: C
Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding? A) hormonal signaling B) autocrine signaling C) paracrine signaling D) endocrine signaling E) synaptic signaling
Answer: C
Which of the following is the best explanation for the fact that most transduction pathways have multiple steps? A) Most of the steps were already in place because they are steps in other pathways. B) Multiple steps in a pathway require the least amount of ATP. C) Multiple steps provide for greater possible amplification of a signal. D) Each individual step can remove excess phosphate groups from the cytoplasm. E) Each step can be activated by several G proteins simultaneously.
Answer: C
An inhibitor of phosphodiesterase activity would have which of the following effects? A) block the response of epinephrine B) decrease the amount of cAMP in the cytoplasm C) block the activation of G proteins in response to epinephrine binding to its receptor D) prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm E) block the activation of protein kinase A
Answer: D
An inhibitor of which of the following could be used to block the release of calcium from the endoplasmic reticulum? A) tyrosine kinases B) serine/threonine kinases C) phosphodiesterase D) phospholipase C E) adenylyl cyclase
Answer: D
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 and therefore diffuses widely. B) Estrogen has specific receptors inside several cell types, but each cell responds in the same way to its binding. 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 of which have different responses to its binding. E) The subcomponents of estrogen, when metabolized, can influence cell response.
Answer: D
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. E) that does any of the above.
Answer: D
In yeast signal transduction, the yeast cells A) must physically and directly interact. B) produce signal molecules that change themselves so they can interact with one another. C) produce response molecules that diffuse to other yeast cells. D) secrete molecules that result in response by other yeast cells. E) mate, after which the new cells secrete hybrid signals.
Answer: D
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
What is most likely to happen to an animal's target cells that lack receptors for local regulators? A) They might compensate by receiving nutrients via a factor. B) They could develop normally in response to neurotransmitters instead. C) They could divide but never reach full size. D) They might not be able to multiply in response to growth factors from nearby cells. E) Hormones would not be able to interact with target cells.
Answer: D
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) receptor B) relay molecule C) transducer D) signal molecule E) endocrine molecule
Answer: D
Which of the following is true of transcription factors? A) They regulate the synthesis of DNA in response to a signal. B) They transcribe ATP into cAMP. C) They initiate the epinephrine response in animal cells. D) They control gene expression. E) They regulate the synthesis of lipids in the cytoplasm.
Answer: D
Because most receptors are membrane proteins, which of the following is usually true? A) They lead to changes in intracellular ion concentration. B) They open and close in response to protein signals. C) They are only attached to one membrane surface: exterior or interior. D) They preferentially bind with lipid or glycolipid signal molecules. E) They change their conformation after binding with signal polypeptides.
Answer: E
Sutherland discovered that epinephrine signals A) a decrease in levels of cAMP as a result of bypassing the plasma membrane. B) lower blood glucose by binding to liver cells. C) interactions with insulin inside muscle cells. D) interactions directly with glycogen phosphorylase. E) elevation of cytosolic concentrations of cyclic AMP.
Answer: E
The function of phosphatases in signal transduction is best described as to 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 transduction signal so it affects multiple transducers. D) amplify the second messengers such as cAMP. E) inactivate protein kinases and turn off the signal transduction.
Answer: E
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 and then enter the cell and eventually the nucleus. 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 phosphodiesterase 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-coupled receptors.
Answer: E
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 signaling B) ligand-gated ion channel signaling C) adenylyl cyclase activity D) phosphatase activity E) receptor tyrosine kinase activity
Answer: E