Cell biology Ch 16

Given the generic signaling pathway in the figure below, select the image label that corresponds to each of the components named below

-receptor protein-> image label 2 -effector proteins-> image label 4 -intracellular signaling proteins image-> label 3 -ligand->image label 1

Others use cytokines, which bind to cytokine receptors. Cytokine receptors have no intrinsic enzyme activity but are associated with cytoplasmic tyrosine kinases called ___B___s, which become activated on the binding of cytokine to its receptor and go on to phosphorylate and activate cytoplasmic transcriptional regulators called ___C___s.

JAK; STAT

Some intracellular signaling pathways involve chains of protein kinases that phosphorylate each other, as seen in the ___D___ signaling module.

MAP Kinase

Some use extracellular signal molecules that are dissolved gases, such as ___A___, which can diffuse easily into cells.

NO

During ___C___ signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells.

Paracrine

target of the G protein for cleavage of inositol phospholipids

Phospholipase C

The rod photoreceptors in the eye are extremely sensitive to light. The cells sense light through a signal transduction cascade involving light activation of a GPCR that activates a G protein that activates cyclic GMP phosphodiesterase. You add a drug that inhibits cyclic GMP phosphodiesterase. How do you predict that the addition of the drug would affect the light-sensing ability of the rod cells?

The drug decrease the light-sensing response

The rod photoreceptors in the eye are extremely sensitive to light. The cells sense light through a signal transduction cascade involving light activation of a GPCR that activates a G protein that activates cyclic GMP phosphodiesterase.You add a drug that is a nonhydrolyzable analog of GTP. How do you predict that the addition of the drug would affect the light-sensing ability of the rod cells?

The drug would increase the light-sensing response

when a cell-surface receptor activates a G protein

The α subunit exchanges its bound GDP for GTP.

Antibodies are Y-shaped molecules that have two identical binding sites. Suppose that you have obtained an antibody that is specific for the extracellular domain of an RTK. When the antibody binds to the RTK, it brings together two RTK molecules. If cells containing the RTK were exposed to the antibody, would you expect the kinase to be activated, inactivated, or unaffected?

activated

target of the G protein for increase in cAMP levels

adenylyl cyclase

Signaling via a steroid hormone receptor leads to

amplification of the original signal

Intracellular signaling proteins can ____C___ the signal received to evoke a strong response from just a few extracellular signal molecules.

amplify

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 ___E___ (which remains embedded in the plasma membrane) and ___F___ (which diffuses into the cytosol).

diacylglycerol; IP3

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________.

diffusing into cells and stimulating guanylyl cyclase directly

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by

diffusing into cells and stimulating the cyclase directly

These intracellular signaling proteins ultimately change the activity of ____B___ proteins that bring about cell responses.

effector

t/f: An amplification of a signal could occur when an extracellular signaling molecule binds and activates a GPCR?

false

t/f: An amplification of a signal could occur when cAMP activates protein kinase A.

false

As shown in the figure above, 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 α subunit activates adenylyl cyclase, thereby increasing cAMP levels. The cAMP molecules then activate a cAMP-dependent kinase (PKA) that, in turn, activates enzymes that result in the breakdown of muscle glycogen, lowering glycogen levels. You obtain muscle cells that lack adenylyl cyclase. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline?

higher

You obtain muscle cells that lack the GPCR. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline?

higher

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

hormone

A cell that receives more than one extracellular signal at the same time can ____D___ this information using intracellular signaling proteins.

integrate

All members of the steroid hormone receptor family

interact with signal molecules that diffuse through the plasma membrane

Most members of the steroid hormone receptor family __________________.

interact with signal molecules that diffuse through the plasma membrane

____G___ inhibits this activity of the α subunit, thereby keeping the subunit in an active state.

cholera toxin

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

contact-dependent signaling-> 1 paracrine signaling-> 2 neuronal signaling -> 3 endocrine signaling -> 4

target of the G protein for changes in membrane potential

ion channels

A protein kinase can act as an integrating device in signaling if it ___________________.

is activated by two or more proteins in different signaling pathways

Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely ____A___ concentration of free Ca2+ in the cytosol, compared with its concentration in the ____B___ space and in the ____C___, creating a steep electrochemical gradient.

low; extracellular; endoplasmic reticulum

You obtain muscle cells that have an α subunit that cannot hydrolyze GTP but can interact properly with the β and γ subunits. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline?

lower

You obtain muscle cells that lack the cAMP phosphodiesterase. In the presence of adrenaline, would glycogen levels in these cells be higher or lower than in normal cells treated with adrenaline?

lower

___D___ signaling converts electrical impulses into a chemical signal.

neuronal

When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as ____D___ which also binds diacylglycerol, and ____E___ ,which activates CaM-kinases.

protein kinase C; calmodulin

Enzymes that phosphorylate proteins, termed ____F___, can also serve as molecular switches; the actions of these enzymes are countered by the activity of ____G___.

protein kinases; protein phosphatses

Cells receive signals through a ___E___, which can be an integral membrane protein or can reside inside the cell

receptor

An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface ____A___ that control intracellular signaling proteins.

receptors

G-protein-coupled receptors (GPCRs) all have a similar structure with ____A___ transmembrane domains.

seven

Which of the following processes involve the combining of a message from one signaling molecule with that of another to either enhance or inhibit a cellular effect?

signal integration

The length of time a G protein will signal is determined by _____________.

the GTPase activity of Gα

When a GPCR binds an extracellular signal, an intracellular G protein, composed of ____B___ subunits, becomes activated.

three

t/f: An amplification of a signal could occur when adenylyl cyclase produces cyclic AMP.

true

t/f: An amplification of a signal could occur when protein kinase A phosphorylates target proteins.

true

t/f: An amplification of a signal could occur when the activated GPCRs cause Gα to separate from Gβ and Gγ.

true

____C___ of the G-protein subunits are tethered to the plasma membrane by short lipid tails.

two

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 below. addition of a high concentration of a non-hydrolyzable analog of GTP

would enhance this effect of the acetylcholine

Which one 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 one 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.

Which one of the following usually happens when a cell-surface receptor activates a heterotrimeric G protein? A. The inactive α subunit exchanges its bound GDP for GTP and becomes activated. B. It activates the α subunit and inactivates the βγ complex. C. The GDP bound to the β subunit is phosphorylated to form bound GTP. D. The β subunit exchanges its bound GDP for GTP

A. The inactive α subunit exchanges its bound GDP for GTP and becomes activated.

The growth factor Superchick stimulates the growth of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK). Many tumor cell lines have mutations in the gene that encodes this receptor. Which one of the following mutations would be expected to promote uncontrolled (or, in other words, hyperactive) cell growth? A. a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor B. a mutation that prevents the binding of the normal extracellular signal to the receptor C. a mutation that prevents dimerization of the receptor D. a mutation that destroys the kinase activity of the receptor

A. a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor

Which of the following is likely to occur more rapidly in response to an extracellular signal? A. changes in cell secretion B. increased cell division

A. changes in cell secretion

Which of the following is likely to occur more rapidly in response to an extracellular signal? A. changes in protein phosphorylation B. changes in proteins being synthesized

A. changes in protein phosphorylation

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

Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. The figure below 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? A. the expression of a constitutively active phospholipase C B. a mutation in the GPCR that binds the signal more tightly C. a Ca2+ channel in the endoplasmic reticulum with an increased affinity for IP3 D. a mutation in the gene that encodes Rafty such that the enzyme can no longer be phosphorylated by PKC

A. the expression of a constitutively active phospholipase C

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.

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.

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which one of the following statements is FALSE? A. Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal. B. Heart muscle cells, salivary gland cells, and skeletal muscle cells all express the same acetylcholine receptor. C. Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. D. Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways.

B. Heart muscle cells, salivary gland cells, and skeletal muscle cells all express the same acetylcholine receptor.

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 figure below shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine? A. a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO B. a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP C. a muscle cell that has cyclic GMP phosphodiesterase constitutively active D. a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO

B. a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP

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 to RGF 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

Which of the following is likely to occur more rapidly in response to an extracellular signal? A. changes in mRNA levels B. changes in membrane potential

B. changes in membrane potential

You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted below. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which of the following situations will lead to an increase in Brainy transcription? A. A mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA. B. A mutation in the nuclear import sequence of PKA from PPKKKRKVto PPAAAAAV. C. A mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive. D. A mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein

C. A mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive.

The figure below shows that intracellular signaling pathways can be highly interconnected. From the information in the above figure, which of the following statements is incorrect? A. The GPCR and the RTK both activate phospholipase C. B. Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators. C. CaM-kinase is only activated when the GPCR is active and not when the RTK is active. D. Ras is activated only when the RTK is active and not when the GPCR is active.

C. CaM-kinase is only activated when the GPCR is active and not when the RTK is active.

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 muscles, 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 GQF.

C. QGF activates different intracellular signaling pathways in heart muscles, fibroblasts, and nerve cells to produce the different responses observed.

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

The figure below shows how normal signaling works with a Ras protein acting downstream of an RTK.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

Acetylcholine acts at a GPCR on heart muscle to make the heart beat more slowly. It does so by ultimately opening K+ channels in the plasma membrane (as shown below),which decreases the cell's excitability by making it harder to depolarize the plasma membrane. Which of the following conditions would increase the effect of acetylcholine? A. addition of a drug that stimulates the GTPase activity of the Gα subunit. B. mutations in the K+ channel that keep it closed all the time. C. modification of the Gα subunit by cholera toxin. D. a mutation that decreases the affinity of the βγ complex of the G protein for the K+ channel. E. a mutation in the acetylcholine receptor that prevents its localization on the cell surface. F. adding acetylcholinesterase to the external environment of the cell.

C. modification of the Gα subunit by cholera toxin.

Akt promotes the survival of many cells. It is activated by an intracellular signaling pathway that is triggered by an RTK that activates PI 3-kinase, as shown below. Which of the following statements is false? A. In the presence of a survival signal, Akt localizes to the plasma membrane by binding to PIP3. B. In the absence of survival signal, Bad inhibits the cell death inhibitor protein Bcl2. C. In the presence of survival signal, the cell death inhibitory protein Bcl2 is active. D. In the absence of survival signal, Bad is phosphorylated.

D. In the absence of survival signal, Bad is phosphorylated.

A signal that must be relayed to the entire body is most efficiently sent by ___A___ cells, which produce hormones that are carried throughout the body through the bloodstream.

Endocrine

___B___ methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events.

Contact-dependent

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as shown below. Which of the following statements below is false? A. A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase. B. A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor. C. A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available. D. A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.

D. A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available

Which one 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 one of the following statements is TRUE? A. A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. B. Any foreign substance that binds to a receptor will always induce the same response as that is produced by the signal molecule. C. All extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. D. Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor.

D. Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor.

When unstimulated, the α subunit is bound to ____D___, which is exchanged for ____E___ on stimulation.

GDP; GTP

____E___ proteins can act as molecular switches, letting a cell know that a signal has been received.

GTP-binding

The intrinsic ____F___ activity of the α subunit is important for inactivating the G protein.

GTPase