Exam 2: Chapter 16

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in the figure below. Which of the following statements is FALSE? (A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available, a constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase, and a constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor are all true)

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

The last common ancestor to plants and animals was a unicellular eukaryote. Thus, it is thought that multicellularity and the attendant demands for cell communication arose independently in these two lineages. This evolutionary viewpoint accounts nicely for the vastly different mechanisms that plants and animals use for cell communication. Fungi use signaling mechanisms and components that are very similar to those used in animals. Which of the phylogenetic trees shown in the figure below does this observation support?

B

The figure below shows that intracellular signaling pathways can be highly interconnected. From the information in the figure, which of the following statements is FALSE? (Ras is activated only when the RTK is active and not when the GPCR is active, the GPCR and the RTK both activate phospholipase C, and activation of either the GPCR or the RTK will lead to activation of transcriptional regulators are all true)

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

Which of the following statements is FALSE? (Some signal molecules are transmembrane proteins, nucleotides and amino acids can act as extracellular signal molecules, and some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription are all true)

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 TRUE?

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

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

GTPase activity of Gα.

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? (Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine whereas skeletal muscle cells contract, heart muscle cells/salivary gland cells/skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal, and active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways are all true)

Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family.

Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2, as diagrammed in the figure. Which of the following statements is FALSE? (In the presence of a survival signal the cell-death inhibitory protein Bcl2 is active, in the absence of a survival signal Bad inhibits the cell-death inhibitor protein Bcl2, and in the presence of a survival signal, Akt is phosphorylated are all true)

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

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

Notch

Which of the following statements is TRUE?

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

Which of the following statements about molecular switches is FALSE? (Serine/threonine kinases are the most common types of protein kinase, protein kinases transfer the terminal phosphate from ATP onto a protein, and a GTP-binding protein exchanges its bound GDP for GTP to become activated are all true)

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

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?

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

Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F is known to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell line B 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 of serum for their response to factor F, with the results summarized in table below. Which of the following cannot be concluded from your results above?

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

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?

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 statements about G-protein-coupled receptors (GPCRs) is FALSE? (GPCRs are the largest family of cell-surface receptors in humans, GPCRs are found in yeast/mice/humans, and GPCRs are used in endocrine/paracrine/neuronal signaling are all true)

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

Which of the following statements is TRUE?

The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.

The following happens when a G-protein-coupled receptor activates a G protein.

The α subunit exchanges its bound GDP for GTP.

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 the table below. Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer.

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

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 the figure below. Which of the following would enhance this effect of the acetylcholine?

addition of a high concentration of a nonhydrolyzable analog of GTP

The ethylene response in plants involves a dimeric transmembrane receptor. When the receptor is not bound to ethylene, the receptor binds to and activates a protein kinase, which activates an intracellular signaling pathway that leads to the degradation of a transcriptional regulator important for transcribing the ethylene-responsive genes (see figure below). You discover a phosphatase that is important for ethylene signaling, and you name it PtpE. Plants lacking PtpE never turn on ethylene-responsive genes, even in the presence of ethylene. You find that PtpE dephosphorylates serine 121 on the transcriptional regulator. Furthermore, plants lacking PtpE degrade the transcriptional regulator in the presence of ethylene. Which of the following statements is inconsistent with your data?

When the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-responsive genes.

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

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 in the figure below. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainy transcription?

a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive

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

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 mutation that prevents RGFR from binding to RGF

You are interested in further understanding the signal transduction pathway that controls the production of Pig1, a protein important for regulating cell size. Activation of the TRK receptor leads to activation of the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE transcription factor. SZE only interacts with the nuclear transport receptor when it is phosphorylated. SZE is a gene activator for the Pig1 gene. This pathway is diagrammed in the figure. Normal cells grown under standard conditions (without ligand) are 14 μm in diameter while normal cells exposed to TRK ligand are 10.5 μm in diameter. Given this situation, which of the following conditions do you predict will more likely lead to smaller cells?

addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE

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?

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

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?

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

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.

contact-dependent

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to

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

Which of the following mechanisms is NOT directly involved in inactivating an activated RTK? (digestion of the RTK in lysosomes, removal of the RTK from the plasma membrane by endocytosis, and dephosphorylation by protein tyrosine phosphatases are involved)

dephosphorylation by serine/threonine phosphatases

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

diffusing into cells and stimulating the cyclase directly.

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

hormone

All members of the nuclear receptor family

interact with signal molecules that diffuse through the plasma membrane.

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

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

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

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?

the expression of a constitutively active phospholipase C