Chapter 16

Which of the following statements about molecular switches is false? (a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. (b) Protein kinases transfer the terminal phosphate from ATP onto a protein. (c) Serine/threonine kinases are the most common types of protein kinase. (d) A GTP-binding protein exchanges its bound GDP for GTP to become activated

(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.

When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is true? (a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras. (b) The cells you create will run out of the GTP necessary to activate Ras. (c) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras. (d) The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.

(a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras

Which of the following mechanisms is not directly involved in inactivating an activated RTK? (a) dephosphorylation by serine/threonine phosphatases (b) dephosphorylation by protein tyrosine phosphatases (c) removal of the RTK from the plasma membrane by endocytosis (d) digestion of the RTK in lysosomes

(a) dephosphorylation by serine/threonine phosphatases Page 16 of 35

Which of the following statements is true? (a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. (b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling. (c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. (d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.

(b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization? (a) a mutation that increases the affinity of RGFR for RGF (b) a mutation that prevents RGFR from binding to RGF (c) changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines (d) changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid

(b) a mutation that prevents RGFR from binding to RGF

Male cockroaches with mutations that strongly decrease the function of an RTK called RTKX are oblivious to the charms of their female comrades. This particular RTK binds to a small molecule secreted by sexually mature females. Most males carrying loss-offunction mutations in the gene for Ras protein are also unable to respond to females. You have just read a paper in which the authors describe how they have screened cockroaches that are mutant in RTKX for additional mutations that partly restore the ability of males to respond to females. These mutations decrease the function of a protein that the authors call Z. Which of the following types of protein could Z be? (a) a protein that activates the Ras protein by causing Ras to exchange GDP for GTP (b) a protein that stimulates hydrolysis of GTP by the Ras protein (c) an adaptor protein that mediates the binding of the RTKX to the Ras protein (d) a transcriptional regulator required for the expression of the Ras gene

(b) a protein that stimulates hydrolysis of GTP by the Ras protein

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3kinase (PI 3-kinase) to _________. (a) activate the RTK. (b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane. (c) directly phosphorylate Akt. (d) to create DAG

(b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________. (a) neurotransmitter. (b) hormone. (c) dissolved gas. (d) scaffold

(b) hormone

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false? (a) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. (b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. (c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. (d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.

(c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways.

Which of the following statements is false? (a) Nucleotides and amino acids can act as extracellular signal molecules. (b) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription. (c) Some signal molecules are transmembrane proteins. (d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids

(d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids

Which of the following statements is false? (a) In the presence of a survival signal, Akt is phosphorylated. (b) In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2. (c) In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active. (d) In the absence of a survival signal, Bad is phosphorylated.

(d) In the absence of a survival signal, Bad is phosphorylated.

Which of the following statements about G-protein-coupled receptors (GPCRs) is false? (a) GPCRs are the largest family of cell-surface receptors in humans. (b) GPCRs are used in endocrine, paracrine, and neuronal signaling. (c) GPCRs are found in yeast, mice, and humans. (d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains

(d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in ______________ signaling. (a) endocrine (b) paracrine (c) neuronal (d) contact-dependent

(d) contact-dependent

All members of the steroid hormone receptor family __________________. (a) are cell-surface receptors. (b) do not undergo conformational changes. (c) are found only in the cytoplasm. (d) interact with signal molecules that diffuse through the plasma membrane.

(d) interact with signal molecules that diffuse through the plasma membrane.

The length of time a G protein will signal is determined by _______. (a) the activity of phosphatases that turn off G proteins by dephosphorylating Gα. (b) the activity of phosphatases that turn GTP into GDP. (c) the degradation of the G protein after Gα separates from Gβγ. (d) the GTPase activity of Gα.

(d) the GTPase activity of Gα.

Which of the following statements is true? (a) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior. (b) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. (c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. (d) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.

(a) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Which of the following statements is true? (a) MAP kinase is important for phosphorylating MAP kinase kinase. (b) PI 3-kinase phosphorylates a lipid in the plasma membrane. (c) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP. (d) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription.

(b) PI 3-kinase phosphorylates a lipid in the plasma membrane.

The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true? (a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. (b) Glial cells do not have a receptor for QGF. (c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. (d) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.

(c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.

The following happens when a G-protein-coupled receptor activates a G protein. (a) The β subunit exchanges its bound GDP for GTP. (b) The GDP bound to the α subunit is phosphorylated to form bound GTP. (c) The α subunit exchanges its bound GDP for GTP. (d) It activates the α subunit and inactivates the βγ complex.

(c) The α subunit exchanges its bound GDP for GTP.

The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation? (a) a mutation that prevents dimerization of the receptor (b) a mutation that destroys the kinase activity of the receptor (c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor (d) a mutation that prevents the binding of the normal extracellular signal to the receptor

(c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor

You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line? (a) addition of a drug that prevents protein X from activating Ras (b) addition of a drug that increases the affinity of protein Y and Ras (c) addition of a drug that blocks protein Y from interacting with its target (d) addition of a drug that increases the activity of protein Y

(c) addition of a drug that blocks protein Y from interacting with its target

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____. (a) killing cells immediately, exerting their physiological effects by causing cell death. (b) diffusing through cell plasma membranes and binding to transcription factors to change gene expression. (c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus. (d) removing cell-surface receptors from the plasma membrane.

(c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus.

A protein kinase can act as an integrating device in signaling if it ___________________. (a) phosphorylates more than one substrate . (b) catalyzes its own phosphorylation. (c) is activated by two or more proteins in different signaling pathways. (d) initiates a phosphorylation cascade involving two or more protein kinases.

(c) is activated by two or more proteins in different signaling pathways.

Circle the phrase in each pair that is likely to occur more rapidly in response to an extracellular signal. A. changes in cell secretion / increased cell division B. changes in protein phosphorylation / changes in proteins being synthesized C. changes in mRNA levels / changes in membrane potential

A. changes in cell secretion B. changes in protein phosphorylation C. changes in membrane potential

Match the target of the G protein with the appropriate signaling outcome. adenylyl cyclase ________ A. cleavage of inositol phospholipids ion channels _________ B. increase in cAMP levels phospholipase C _________ C. changes in membrane potential

B C A

Rank the following types of cell signaling from 1 to 4, with 1 representing the type of signaling in which the signal molecule travels the least distance and 4 the type of signaling in which the signal molecule travels the largest distance ______ paracrine signaling ______ contact-dependent signaling ______ neuronal signaling ______endocrine signaling

____3__ paracrine signaling ____1__ contact-dependent signaling ____2__ neuronal signaling ____4__ endocrine signaling

You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells? (a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive (b) addition of a drug that prevents GTP hydrolysis by Gα (c) addition of a drug that activates adenylyl cyclase (d) addition of a drug that mimics the ligand of ERC1

a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive