Exam 16: Cell Signaling

During the mating process, yeast cells respond to pheromones secreted by other yeast cells.These pheromones bind GPCRs on the surface of the responding cell and lead to the activation of G proteins inside the cell.When a wild-type yeast cell senses the pheromone, its physiology changes in preparation for mating: the cell stops growing until it finds a mating partner.If yeast cells do not undergo the appropriate response after sensing a pheromone, they are considered sterile.Yeast cells that are defective in one or more components of the G protein have characteristic phenotypes in the absence and presence of the pheromone, which are listed in Table 16-14. mutation minus pheromone plus pheromone none (wild type) normal growth arrested growth, mating response \alpha subunit deleted arrested growth arrested growth, sterile \beta subunit deleted normal growth normal growth, sterile \gamma subunit deleted normal growth normal growth, sterile \alpha and \beta deleted normal growth normal growth, sterile \alpha and \gamma deleted normal growth normal growth, sterile \beta and \gamma deleted normal growth normal growth, sterile Table 16-14 Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer.

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once. cyclic GMP IGF NO Delta phosphodiesterase diacylglycerol MAP kinase Ras Cells signal to one another in various ways.Some use extracellular signal molecules that are dissolved gases, such as __________ which can diffuse easily into cells.Most receptor tyrosine kinases activate __________ , a small GTP-binding protein found at the cytosolic face of the plasma membrane.Some intracellular signaling pathways involve a series of protein kinases that phosphorylate each other, as seen in the __________ signaling module.Lipids can also relay signals in the cell, as we observe when phospholipase C cleaves the sugar-phosphate head off a lipid molecule to generate the two small messenger molecules __________ (which remains embedded in the plasma membrane) and __________ (which diffuses into the cytosol).

When the cytosolic tail of the __________ receptor is cleaved, it migrates to the nucleus and affects gene regulation.

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once. amplification G protein phosphorylation contact-dependent K⁺ channel receptor endocrine neuronal target epithelial paracrine Cells can signal to each other in various ways.A signal that must be relayed to the entire body is most efficiently sent by __________ cells, which produce hormones that are carried throughout the body through the bloodstream.On the other hand, __________ methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events.During __________ signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells.Finally, __________ signaling involves the conversion of electrical impulses into a chemical signal.Cells receive signals through a __________, which can be an integral membrane protein or can reside inside the cell.

Two protein kinases, PK1 and PK2, work sequentially in an intracellular signaling pathway.You create cells that contain inactivating mutations in the genes that encode either PK1 or PK2 and find that these cells no longer respond to a particular extracellular signal.You also create cells containing a version of PK1 that is permanently active and find that the cells behave as though they are receiving the signal even when the signal is not present.When you introduce the permanently active version of PK1 into cells that have an inactivating mutation in PK2, you find that these cells also behave as though they are receiving the signal even when no signal is present. A.From these results, does PK1 activate PK2, or does PK2 activate PK1? Explain your answer. B.You now create a permanently active version of PK2 and find that cells containing this version behave as though they are receiving the signal even when the signal is not present.What do you predict will happen if you introduce the permanently active version of PK2 into cells that have an inactivating mutation in PK1?

Which of the following statements is TRUE?

Foreign substances like nicotine, morphine, and menthol exert their initial effects by

All members of the nuclear receptor family

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?

For each of the following sentences, select the best word or phrase from the list below to fill in the blanks.Not all words or phrases will be used; each word or phrase should be used only once. acetylase decouple GTP-binding AMP-binding decrease neurotransmitter amplify effector protein kinases autocrine esterases protein phosphatases cleavage integrate receptors convolute GMP-binding sterols An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface __________ that control intracellular signaling proteins.These intracellular signaling proteins ultimately change the activity of __________ proteins that bring about cell responses.Intracellular signaling proteins can __________ the signal received to evoke a strong response from just a few extracellular signal molecules.A cell that receives more than one extracellular signal at the same time can __________ this information using intracellular signaling proteins.__________ proteins can act as molecular switches, letting a cell know that a signal has been received.Enzymes that phosphorylate proteins, termed __________, can also serve as molecular switches; the actions of these enzymes are countered by the activity of __________.

Which of the following statements is TRUE?

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a

Bacteria undergo chemotaxis toward amino acids, which usually indicates the presence of a food source.Chemotaxis receptors bind a particular amino acid and cause changes in the bacterial cell that induce the cell to move toward the source of the amino acid.Four types of chemotaxis receptor that mediate responses to different amino acids have been identified in a bacterium.The receptors are called ChrA, ChrB, ChrC, and ChrD.Each receptor specifically senses serine, aspartate, glutamate, or glycine, although you do not know which receptor senses which amino acid.You have been given a wild-type bacterial strain that contains all four receptors, as well as various mutant bacterial strains that are lacking one or more of the receptors.To figure out which receptor senses which amino acid, you conduct experiments in which you fill a capillary tube with an amino acid to attract the bacteria, dip the capillary tube into a solution containing bacteria, remove the capillary tube after 5 minutes, and count the number of bacteria in the capillary tube.Your results are shown in Table 16-26. strain intact receptors serine aspartate glutamate glycine none 1 ChrA, ChrB, ChrC, ChrD 590 1050 950 66 5 2 ChrA, ChrB, ChrC 7 840 770 130 8 3 ChrC, ChrD 340 7 590 6 6 4 ChrA, ChrC, ChrD 550 6 650 41 5 5 ChrB, ChrC, ChrD 700 590 850 9 8 Table 16-26 From these results, indicate which receptor is used for which amino acid.

When adrenaline binds to adrenergic receptors on the surface of a muscle cell, it activates a G protein, initiating an intracellular signaling pathway in which the activated ? subunit activates adenylyl cyclase, thereby increasing cAMP levels in the cell.The cAMP molecules then activate a cAMP-dependent kinase (PKA) that, in turn, activates enzymes that result in the breakdown of muscle glycogen, thus lowering glycogen levels.You obtain muscle cells that are defective in various components of the signaling pathway.Referring to Figure 16-20, indicate how glycogen levels would be affected in the presence of adrenaline in the following cells.Would they be higher or lower than in normal cells treated with adrenaline? A.cells that lack adenylyl cyclase B.cells that lack the GPCR C.cells that lack cAMP phosphodiesterase D.cells that have an ? subunit that cannot hydrolyze GTP but can interact properly with the ? and ? subunits

A calmodulin-regulated kinase (CaM-kinase) is involved in spatial learning and memory.This kinase is able to phosphorylate itself such that its kinase activity is now independent of the intracellular concentration of Ca²⁺.Thus, the kinase stays active after Ca²⁺ levels have dropped.Mice completely lacking this CaM-kinase have severe spatial learning defects but are otherwise normal. A.Each of the following mutations also leads to similar learning defects.For each case explain why. (1) a mutation that prevents the kinase from binding ATP (2) a mutation that deletes the calmodulin-binding part of the kinase (3) a mutation that destroys the site of autophosphorylation B.What would be the effect on the activity of CaM-kinase if there were a mutation that reduced its interaction with the protein phosphatase responsible for inactivating the kinase?

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?

Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC.Figure 16-17 shows how G proteins can indirectly activate PKC.You have discovered the enzyme activated by PKC that mediates the lipid modification.You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is active; these lipid modifications can be detected by dyes that bind to the modified lipids.Cells lacking Rafty do not have these modifications, even when PKC is active.Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty? Figure 16-17

Receipt of extracellular signals can change cell behavior quickly (for example, in seconds or less) or much more slowly (for example, in hours). A.What kind of molecular changes could cause quick changes in cell behavior? B.What kind of molecular changes could cause slow changes in cell behavior? C.Explain why the response you named in A results in a quick change, whereas the response you named in B results in a slow change.

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?

Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly.The activated receptor stimulates a G protein, which opens a K⁺ channel in the plasma membrane, as shown in Figure 16-13.Which of the following would enhance this effect of the acetylcholine? Figure 16-13