Chapter 16

Two protein kinases, PK1 and PK2, work sequentially in an intracellular signaling pathway. Youcreate cells that contain inactivating mutations in the genes that encode either PK1 or PK2 and findthat these cells no longer respond to a particular extracellular signal. You also create cells containinga version of PK1 that is permanently active and find that the cells behave as though they arereceiving the signal even when the signal is not present. When you introduce the permanently activeversion o

PK1 activates PK2

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

a. Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor to signal a target cell to change its behavior. Hydrophilic molecules can not diffuse the membrane, can only affect a cell through a receptor, the intracellular domain mediates signal transduction.

1. You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 isimportant in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activatesadenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lackERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activatedversion of PKA are 15% larger than normal cells. Given these results, which of the followingtreat

a. addition of a drug that causes cyclic AMP Hyperactivating cyclic AMP will degrade it, terminating the signal quicker.

Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activatedreceptor stimulates a G protein, which opens a K+ channel in the plasma membrane (see Fig. 16-17in ECB, 5th edition). Which of the following would enhance this effect of the acetylcholine? a. addition of a high concentration of a nonhydrolyzable analog of GTP b. addition of a drug that prevents the α subunit from exchanging GDP for GTP c. mutations in the acetylcholine receptor that weaken the interac

a. addition of a high concentration of a nonhydrolyzable analog of GTP

3. 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 a

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. Only skeletal muscle cells express acetylcholine in transmitter-gated ion channel

Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F isknown to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell lineB does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B,using recombinant DNA techniques. You then test all of your various cell lines in the presence ofserum for their response to factor F, with the results summarized in Table 1. Which of t

b. Receptor R binds to factor F to induce cell proliferation in cell line A.

. 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 paracrinesignaling. c. Paracrine signaling involves the secretion of signals into the bloodstream for distributionthroughout the organism. d. The axons of neurons typically signal target cells using membrane-bound signaling molecules thatact on receptors

b. The regulation of inflammatory responses at the site of an infection is an example of paracrinesignaling. Paracrine signaling will be more local

During the mating process, yeast cells respond to pheromones secreted by other yeast cells. Thesepheromones bind GPCRs on the surface of the responding cell and lead to the activation of Gproteins inside the cell. When a wild-type yeast cell senses the pheromone, its physiology changes inpreparation for mating: the cell stops growing until it finds a mating partner. If yeast cells do notundergo the appropriate response after sensing a pheromone, they are considered sterile. Yeast cellsthat are d

b. The βγ subunit activates the mating response but is inhibited when bound to α.

15. The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (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. 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 mostsuited for this is a a. neurotransmitter. b. hormone. c. dissolved gas. d. scaffold

b. hormone.

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.

12. The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by a. activating a G protein. b. activating a receptor tyrosine kinase. c. diffusing into cells and stimulating the cyclase directly. d. activating an intracellular protein kinase.

c. diffusing into cells and stimulating the cyclase directly.

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 geneexpression. c. interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately inthe 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 inthe absence of the normal stimulus.

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

d. GTPase activity of Gα.

3. For each of the following sentences, select the best word or phrase from the list below to fill in theblanks. Not all words or phrases will be used; each word or phrase should be used only once adenylyl cyclase cholera toxin GTPaseAMP diacylglycerol phosphodiesteraseATP five seven ATPase four three Ca2+ GDP twelve cAMP GTP two G-protein-coupled receptors (GPCRs) all have a similar structure with __________ transmembranedomains. When a GPCR binds an extracellular signal, an intracel

seven three two GDP GTP GTPase Cholera Toxin