Test 3 BIOL 4004

Why do you suppose it is much easier to add tubulin dimers to existing microtubules than to start a new microtubule from scratch?

A. More contacts are available at the end of a microtubule.

B. It is easier for tubulin to find the end of a microtubule.

C. Tubulins slide along a microtubule till reaching the end.

D. Individual tubulin dimers do not bind to one another.

A. More contacts are available at the end of a microtubule.

What is the term for the property of sudden conversion of a microtubule from growth to shrinkage, and vice versa?

A. Rescue

B. Catastrophe

C. Dynamic instability

D. Treadmilling

C. Dynamic instability

T/F: Anticancer drugs like paclitaxel and colchicine are used to kill certain kinds of tumor cells because these drugs are not toxic to rapidly dividing normal cells.

False

GTP hydrolysis and whether GTP or GDP is bound to tubulin is an important mechanism to control the dynamic instability of microtubules. Certain aspects of dynamic instability can be viewed using GFP-EB1. Which process(es) is it useful for visualizing and why?

A. Growing and shrinking microtubules, because EB1 binds to the GDP-tubulin cap on microtubules

B. Growing microtubules, because EB1 binds to the GTP-tubulin cap on microtubules

C. Growing and shrinking microtubules, because EB1 binds to the GTP-tubulin cap on microtubules

D. Shrinking microtubules, because EB1 binds to the GTP-tubulin cap on microtubules

B. Growing microtubules, because EB1 binds to the GTP-tubulin cap on microtubules

How would the microtubule dynamics change after adding a non-hydrolyzable analog of GTP to the cells?

A. Microtubule dynamics would not change.

B. Dynamic instability would increase as microtubules rapidly switch between growing and shrinking.

C. Microtubules would grow longer.

D. Microtubules would shrink.

C. Microtubules would grow longer.

When cells enter mitosis, their existing array of cytoplasmic microtubules must be rapidly broken down and replaced with the mitotic spindle, which pulls the chromosomes into the daughter cells. The enzyme katanin, named after Japanese samurai swords, is activated during the onset of mitosis. Katanin extracts tubulin subunits from the wall of cellular microtubules, weakening its structure and promoting breakage. What do you suppose is the usual fate of the microtubule fragments created by katanin?

A. The fragments depolymerize because they contain GDP-tubulin.

B. The fragments serve as seeds for growth from their plus ends.

C. The fragments are joined to rapidly form mitotic microtubules.

D. The fragments are rapidly stabilized by end-binding proteins.

A. The fragments depolymerize because they contain GDP-tubulin.

Mice that are homozygous for a knockout of the gene for the kinesin motor protein KIF1B die at birth. Heterozygous knockouts (one copy deleted) survive but suffer from a progressive muscle weakness similar to human neuropathies. Humans with Charcot-Marie-Tooth disease type 2A have a mutation in one copy of the gene for KIF1B that prevents the protein from binding to ATP. The heterozygous mice and the human patients have very similar progressive neuropathies.How do you suppose that the loss of one copy of a gene for a kinesin motor can have such profound effects on nerve function?

A. The normal gene produces twice as much kinesin but can't keep doing so.

B. Half the usual amount of kinesin cannot keep up with the needs of nerves.

C. The mouse knockout is recessive; one normal gene makes enough kinesin.

D. The human gene with a point mutation makes slow moving kinesin motors.

B. Half the usual amount of kinesin cannot keep up with the needs of nerves.

Which of the following defects have been found in individuals with one of a set of disorders known as ciliopathies?

I Defects in intraflagellar transport (IFT)

II Defects in the primary cilium

III Defects in the basal body

IV Defects in myosin motor proteins

A. I, II, and III

B. II, III, and IV

C. I and IV

D. I, II, and IV

A. I, II, and III

T/F: Communication among cytoskeletal elements coordinates whole-cell polarization and locomotion.

True

What is the term for the collection of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell its shape and the capacity for directed movement?

A. Cytoskeleton

B. Microtubules

C. Actin filaments

D. Intermediate filaments

A. Cytoskeleton

T/F: Actin filaments are responsible for large-scale cellular polarity, enabling cells to tell the difference between top and bottom, or front and back.

False

What is the term for the linear chain of protein subunits joined end-to-end, which associates laterally with other such chains to form a microtubule?

A. Actin filament

B. Intermediate filament

C. Protofilament

D. Stress fiber

C. Protofilament

Which of the following statements correctly describe a role of an accessory protein in the regulation of cytoskeletal filaments?

I Accessory proteins regulate the synthesis of the filament subunits.

II Accessory proteins change the kinetics of filament assembly and disassembly.

III Accessory proteins link filaments to other cell structures such as organelles and the plasma membrane.

A. I and II

B. I and III

C. I, II, and III

D. II and III

D. II and III

What is the term for the bundle of microtubules and associated proteins that forms the core of a cilium or flagellum in a eukaryotic cell and is responsible for their movements?

A. Centriole

B. Flagellin

C. Dynactin

D. Axoneme

D. Axoneme

T/F: Basal bodies firmly root nonmotile primary cilia, but not motile cilia, to the cell surface.

False

Which one of the following statements about kinesins and dyneins and their roles in the behavior of intracellular membranes is correct?

A. Kinesins move Golgi vesicles to the cell interior by dragging them toward microtubule minus ends.

B. Dyneins move Golgi vesicles to the cell periphery by dragging them toward microtubule minus ends.

C. Dyneins move ER membranes to the cell interior by dragging them toward microtubule plus ends.

D. Kinesins move ER membranes to the cell periphery by dragging them toward microtubule plus ends.

D. Kinesins move ER membranes to the cell periphery by dragging them toward microtubule plus ends.

Which one of the following statements correctly describes the roles of kinesin-13 and XMAP215 at the plus ends of microtubules?

A. Kinesin-13 induces catastrophe and disassembly; XMAP215 stabilizes plus ends and hastens assembly.

B. Kinesin-13 stabilizes ends and accelerates assembly; XMAP215 induces catastrophe and disassembly.

C. Kinesin-13 stabilizes ends and hastens assembly; XMAP215 stabilizes plus ends and hastens assembly.

D. Kinesin-13 induces catastrophe and disassembly; XMAP215 stimulates catastrophe and disassembly.

A. Kinesin-13 induces catastrophe and disassembly; XMAP215 stabilizes plus ends and hastens assembly.

What is the term for the centrally located organelle of animal cells that is the primary microtubule-organizing center (MTOC) and acts as the spindle pole during mitosis

A. Axoneme

B. Centriole

C. Centrosome

D. γ-Tubulin ring complex (γ-TuRC)

C. Centrosome

The orientation of the αβ-tubulin dimer in a microtubule was determined in several ways. GTP-coated fluorescent beads, for example, were found to bind exclusively at the plus ends of microtubules.How does this observation define the orientation of the αβ-tubulin dimer in the microtubule? Which tubulin subunit, α or β, is at which end?

A. GTP binds to β-tubulin so it must be at the plus ends.

B. GTP binds to α-tubulin so it must be at the plus ends.

C. GTP binds to β-tubulin so it must be at the minus ends.

D. GTP binds to α-tubulin so it must be at the minus ends.

A. GTP binds to β-tubulin so it must be at the plus ends.

What is the term for the process by which a polymeric protein filament gains subunits at one end while simultaneously losing subunits from the other end?

A. Nucleotide hydrolysis

B. Treadmilling

C. Nucleation

D. Critical concentration

B. Treadmilling

Some actin-binding accessory proteins significantly increase the rate at which the formation of actin filaments is initiated in the cytosol. How might such proteins do this? What must they not do when binding the actin monomers?

A. They promote polymerization by destabilizing complexes of monomers; they must not bind to ends required for polymerization.

B. They promote polymerization by destabilizing complexes of monomers; they must not bind to the sides of the actin monomers.

C. They promote polymerization by stabilizing complexes of monomers; they must not bind to the sides of the actin monomers.

D. They promote polymerization by stabilizing complexes of monomers; they must not bind to ends required for polymerization.

D. They promote polymerization by stabilizing complexes of monomers; they must not bind to ends required for polymerization.

What is the term for the protein assembly that nucleates actin filament growth from the minus end, allowing rapid growth at the plus end and forming a treelike web of filaments?

A. Profilin

B. Arp2/3 complex

C. Formin

D. Thymosin

B. Arp2/3 complex

Most eukaryotic cells maintain the concentration of actin monomers well above the critical concentration needed for actin polymerization in the test tube. In most cells, the excess actin monomers are bound by the protein profilin, which regulates their addition to actin filaments.Why is this strategy advantageous for the cell?

A. Profilin allows actin monomers to be recruited to sites of filament growth.

B. Profilin binding ensures that the cell will not run out of actin monomers.

C. Profilin prevents cells from making excessive numbers of actin filaments.

D. Profilin lowers the critical concentration of actin so filaments can grow.

A. Profilin allows actin monomers to be recruited to sites of filament growth.

The adult animal seethes with crawling cells. Macrophages and neutrophils, for example, crawl to sites of infection and engulf foreign invaders as a critical part of the innate immune response.Which of the following statements correctly describes the individual processes that make up the crawling movement of cells?

I Protrusion pushes out the leading edge of the plasma membrane at the front end of the cell.

II Adhesion to the surface allows the internal actin cytoskeleton to connect to the substratum.

III Contraction of bundles of actin filaments and kinesin motor proteins at the rear of the cell enables translocation.

A. II and III

B. I and II

C. I and III

D. I

B. I and II

Myosin II bipolar thick filaments slide actin filaments toward one another to bring about muscle contraction. What arrangement of actin filaments is necessary for myosin to bring about contraction?

A. The actin filament plus ends must face one another.

B. An actin filament minus end must face an actin plus end.

C. The arrangement of plus and minus ends is irrelevant.

D. The actin filament minus ends must face one another.

D. The actin filament minus ends must face one another.

Rigor mortis occurs in muscle cells after death and is characterized by muscles being locked in a contracted state where myosin is bound to actin. What could be added to the muscle cell to release the rigor state?

A. Pi

B. ADP + Pi

C. ADP

D. ATP

D. ATP

Which one of the following changes takes place when a skeletal muscle contracts?

A. Sarcomeres become shorter

B. Z discs move farther apart.

C. Myosin filaments contract.

D. Actin filaments contract.

A. Sarcomeres become shorter

Which of the following would increase the level of muscle contraction?

Choose one or more:

A. addition of a leaky Ca2+ channel to the sarcoplasmic reticulum

B. addition of a molecule to bind free Ca2+

C. mutation in troponin such that it no longer binds tropomyosin

D. blockage of the Ca2+ pump

A. addition of a leaky Ca2+ channel to the sarcoplasmic reticulum

D. blockage of the Ca2+ pump

T/F: Except for one single type of myosin motor protein, all other members of the 37 distinct families in the myosin superfamily move toward the plus end of an actin filament.

True

Which of the following statements are consistent with the structure and function of intermediate filaments?

Choose one or more:

A. Intermediate filaments protect cells from mechanical stress because they have high tensile strength and resist stretching.

B. Each filament is made of eight strands, and each strand is made from staggered tetramers linked end-to-end.

C. Intermediate filaments can connect cells at cell-cell junctions called desmosomes.

D. Intermediate filaments are constructed of identical subunits found in all eukaryotic cells.

A. Intermediate filaments protect cells from mechanical stress because they have high tensile strength and resist stretching.

B. Each filament is made of eight strands, and each strand is made from staggered tetramers linked end-to-end.

C. Intermediate filaments can connect cells at cell-cell junctions called desmosomes.

Mutation of the muscle-specific intermediate filament desmin leads to the rare disease desmin-related myopathy. This disorder starts with weakness of the lower limbs when patients are in their 20s or 30s. As symptoms worsen, weakness in respiratory and cardiac muscles occurs, which can lead to serious problems including sudden cardiac arrest.Which of the following mutations would disrupt desmin intermediate filament structure or function and could explain the symptoms of desmin-related myopathy? Choose all of the possible mutations.

Choose one or more:

A. Alteration in head groups, so tetramers are unable to link end-to-end.

B. Alteration in the twist or coiling of the dimers, blocking formation of staggered tetramers.

C. Disruption of the polarity of the final desmin strands.

D. Mutation such that formation of dimers is blocked.

A. Alteration in head groups, so tetramers are unable to link end-to-end.

B. Alteration in the twist or coiling of the dimers, blocking formation of staggered tetramers.

D. Mutation such that formation of dimers is blocked.

There are no known motor proteins that move on intermediate filaments. Which one of the following hypotheses best explains this observation?

A. The rope-like intermediate filaments are too flexible for motors to navigate.

B. Intermediate filaments have no polarity, providing no motor directionality.

C. Because some cells lack intermediate filaments, motors are not necessary.

D. Intermediate filament building blocks are too big for a motor's step length.

B. Intermediate filaments have no polarity, providing no motor directionality.

What is the term for a member of a family of proteins that mediate Ca2+-dependent cell-cell adhesion in animal tissues?

A. Integrin

B. Cadherin

C. Catenin

D. Claudin

B. Cadherin

Cortical tension in an unattached cell gives it a spherical shape, much like surface tension produces the spherical shape of a water droplet. Which one of the following statements correctly describes the basis for cortical tension in unattached cells?

A. Cortical tension is caused by the higher concentration of ions in the cell's interior.

B. Cortical tension is caused by lipid molecules that hold the cell membrane together.

C. Cortical tension is caused by water molecules that bind together at the cell surface.

D. Cortical tension is caused by contraction of actin-myosin bundles at the cell cortex.

D. Cortical tension is caused by contraction of actin-myosin bundles at the cell cortex.

What is the term for the type of anchoring junction that links the intermediate filaments in two adjoining cells?

A. Desmosome

B. Hemidesmosome

C. Tight junction

D. Adherens junction

A. Desmosome

You've just eaten a slice of pecan pie. When the nutrients in the pie reach your gut, they will be moved across the gut epithelium by transporters in its apical and basolateral domains.Which one of the following statements correctly describes the mode of glucose transcellular transport across the gut epithelium?

A. Glucose will be transported passively across the apical membrane and passively across the basolateral membrane.

B. Glucose will be transported passively across the apical membrane and actively across the basolateral membrane.

C. Glucose will be transported actively across the apical membrane and actively across the basolateral membrane.

D. Glucose will be transported actively across the apical membrane and passively across the basolateral membrane.

D. Glucose will be transported actively across the apical membrane and passively across the basolateral membrane.

T/F: Although cadherins and Ig family members are frequently expressed on the same cells, the adhesions mediated by Ig molecules are much stronger and, thus, are largely responsible for holding cells together.

False

What is the general term for the common cell type in connective tissue that secretes an extracellular matrix rich in collagen and other extracellular matrix macromolecules?

A. Fibroblast

B. Glycosaminoglycan

C. Chondrocyte

D. Osteoblast

A. Fibroblast

T/F: The extracellular matrix is a relatively inert scaffold that stabilizes the structure of tissues.

False

What is the general name for a long, linear, highly charged polysaccharide—composed of a repeating pair of sugars, one of which is always an amino sugar—that is found covalently linked to a protein core in the extracellular matrix?

A. Glycosaminoglycan

B. Collagen

C. Laminin

D. Glycoprotein

A. Glycosaminoglycan

Proteoglycans are clearly distinguished from other glycoproteins by each of the following characteristics EXCEPT:

A. Proteoglycans often contain as much as 95% carbohydrate by mass.

B. At least one of the sugar side chains of a proteoglycan must be GAG.

C. GAG chains are long and unbranched, typically about 80 sugars long.

D. In proteoglycans, asparagine residues link GAGs to the core proteins.

D. In proteoglycans, asparagine residues link GAGs to the core proteins.

Which one of the following statements correctly describes how collagen fibrils react to forces in the extracellular matrix?

A. Collagen fibrils form structures that enhance compressive forces.

B. Collagen fibrils form structures that resist compressive forces.

C. Collagen fibrils form structures that enhance tensile forces.

D. Collagen fibrils form structures that resist tensile forces.

D. Collagen fibrils form structures that resist tensile forces.

What is the term for the hydrophobic protein that forms extracellular extensible fibers that give tissues their stretchability and resilience?

A. Proteoglycan

B. Hyaluronan

C. Elastin

D. Collagen

C. Elastin

T/F: Fibroblasts influence the alignment of the collagen fibers, and the collagen fibers in turn affect the distribution of the fibroblasts.

True

Fibronectin can exist both in a soluble form, circulating in the blood and other body fluids, and as insoluble fibronectin fibrils, in which fibronectin dimers are cross-linked to one another by additional disulfide bonds and form part of the extracellular matrix.What aspect of its cell biology allows soluble fibronectin to form insoluble fibronectin fibrils?

A. Fibronectins unfold and pair when mechanically stretched by interaction with the matrix.

B. Fibronectins unfold and pair when the elastin network to which they are linked stretches.

C. Fibronectins unfold and pair when stretched by ties to the intermediate-filament network.

D. Fibronectins unfold and pair when stretched by integrin-mediated links to actin filaments.

D. Fibronectins unfold and pair when stretched by integrin-mediated links to actin filaments.

T/F: A sheet of basal lamina underlies all epithelia.

True

T/F: A proteoglycan in the basal lamina of the kidney glomerulus plays a critical role in filtering the molecules that pass from the bloodstream into the urine.

True

What is the term for the extracellular matrix protein that is the primary organizer of the sheetlike structure of the basal lamina?

A. Integrin

B. Elastin

C. Fibronectin

D. Laminin

D. Laminin

T/F: Several forms of muscular dystrophy (muscle-wasting diseases) arise from defective components in the basal lamina that surrounds muscle fibers.

True

The unusually thick basal lamina of the kidney glomerulus is a key component of the complex molecular filter that controls passage of solutes into the urine. Typically, 180 L of fluid are filtered through the kidneys each day, but most is reabsorbed, with only about 1.5 L being released as urine. The initial filtration is size, shape, and charge selective.The effective pore size is smaller for negatively charged solutes than it is for positively charged solutes of the same size. What features of the basal lamina do you suppose might contribute to this difference in filtration of charged molecules?

A. The basal lamina is made up of many negatively charged molecules.

B. Negatively charged solutes occupy more volume than positive ones.

C. The basal lamina is mostly built from positively charged molecules.

D. The pores through the basal lamina are lined with positive charges.

A. The basal lamina is made up of many negatively charged molecules.

A first step during infection is the attachment of microorganisms to various host proteins, which often include those in the basal lamina of epithelial sheets that form the lining of the gut or the epidermal covering of the skin. Some microorganisms then secrete enzymes that can digest the protein or carbohydrate components of the basal lamina.Why do you suppose microorganisms digest the basal lamina during the infection process?

A. They digest the lamina to obtain cell access, so they can kill it.

B. They digest the lamina to cross to the interior of the organism.

C. They digest the lamina to dig holes to hide from host defenses.

D. They digest the lamina to supply nutrients for bacterial growth.

B. They digest the lamina to cross to the interior of the organism.

T/F: Glycoproteins in the extracellular matrix serve as a reservoir for numerous signaling peptides and proteins; however, the glycoproteins themselves do not produce biological signals by binding to cell-surface receptors.

False

T/F: Various types of integrins connect extracellular binding sites to all the different kinds of internal cytoskeletal elements, including actin filaments, microtubules, and intermediate filaments.

False

Humans contain 24 types of integrins, which are formed from the products of 8 different β-chain genes and 18 different α-chain genes that dimerize in different combinations. The β1 integrin subunit is found on almost all vertebrate cells, and the β2 subunit is found on white blood cells. Defects in various integrin chains cause a variety of diseases.Mutations of which, if either, of the integrin β chains—β1 or β2—would you expect to cause a more severe phenotype?

A. Mutation of the β1 gene would be more severe than a mutation of β2.

B. Mutation of the β2 gene would be more severe than a mutation of β1.

C. Mutation of the β1 or β2 genes does not cause disease phenotypes.

D. Mutation of the β1 or β2 genes would give equally severe phenotypes.

A. Mutation of the β1 gene would be more severe than a mutation of β2.

T/F: Integrins are thought to be rigid rods that span the membrane and link binding sites outside the cell to those inside the cell.

False

Which one of the following statements accurately reflects an aspect of anchorage dependence?

A. Cell growth and proliferation do not depend on attachment to the extracellular matrix.

B. Cells that lose their dependence on the matrix don't survive; thus, don't cause cancer.

C. Cells generate intracellular signals at cell-matrix junctions that are crucial for survival.

D. Cells in matrix-coated dishes model the way connective tissue cells bind to the matrix.

C. Cells generate intracellular signals at cell-matrix junctions that are crucial for survival.

What is the term for the short-range cell-cell communication via secreted local mediators that act on cells in their immediate environment?

A. Contact-dependent signaling

B. Synaptic signaling

C. Paracrine signaling

D. Endocrine signaling

C. Paracrine signaling

T/F: There is no fundamental chemical distinction between signaling molecules that bind to cell-surface receptors and those that bind to intracellular receptors.

False

T/F: Cell-surface receptor proteins act as signal transducers by converting an extracellular ligand-binding event into intracellular signals that alter the behavior of the target cells.

True

What is the term for the protein that organizes groups of interacting intracellular signaling proteins into signaling complexes?

A. Intracellular receptor

B. Kinase cascade

C. Interaction domain

D. Scaffold protein

D. Scaffold protein

What is the term for the cell-cell communication in which the signal molecule remains bound to the signaling cell and only influences cells that physically touch it?

A. Paracrine signaling

B. Endocrine signaling

C. Synaptic signaling

D. Contact-dependent signaling

D. Contact-dependent signaling

What is the general term for a protein that binds a specific extracellular molecule and initiates a response in the cell?

A. Carrier protein

B. Second messenger

C. Receptor

D. Ligand

C. Receptor

Two main classes of molecular switches involve changes in phosphorylation state or changes in guanine nucleotide binding. Which of the following statements about these molecular switches are true?

I In phosphorylation, protein kinases always turn proteins on, whereas protein phosphatases always turn proteins off.

II In guanine nucleotide binding, guanine nucleotide exchange factors (GEFs) always turn proteins on, whereas GTPase-activating proteins (GAPs) always turn proteins off.

A. II

B. Neither

C. I and II

D. I

A. II

What is the term for the protein that binds to a GTP-binding protein and stimulates the hydrolysis of its bound GTP to GDP, converting the GTP-binding protein to its "off" state?

A. GTPase-activating protein (GAP)

B. Protein kinase

C. Guanine nucleotide exchange factor (GEF)

D. GTP-binding protein

A. GTPase-activating protein (GAP)

What is the name of the protein that binds to a GTP-binding protein and activates it by stimulating release of tightly bound GDP, thereby allowing it to bind GTP?

A. GTPase-activating protein (GAP)

B. Guanine nucleotide exchange factor (GEF)

C. Heterotrimeric GTP binding protein (G protein)

D. Monomeric GTPase

B. Guanine nucleotide exchange factor (GEF)

When epinephrine binds to its receptors on the surface of a muscle cell, it activates a G protein, initiating a signaling pathway that results in breakdown of muscle glycogen to produce glucose to meet the cell's anticipated energy needs. Consider how glycogen breakdown would be affected if muscle cells were injected with a nonhydrolyzable analog of GTP, which can't be converted to GDP.

What would happen if the cells were briefly exposed to epinephrine just after they were injected with the nonhydrolyzable GTP analog?

A. Glycogen breakdown would occur for a shorter time in the presence of the analog.

B. Glycogen breakdown would occur for a longer time in the presence of the analog.

C. Glycogen breakdown would not occur at all in the presence of the GTP analog.

D. Glycogen breakdown would occur for the normal time in the presence of the analog.

B. Glycogen breakdown would occur for a longer time in the presence of the analog.

GPCRs activate G proteins by reducing the strength of GDP binding, allowing GDP to dissociate and GTP, which is present at much higher concentrations, to bind. How would the activity of a G protein be affected by a mutation that caused its affinity for GDP to be reduced without significantly changing its affinity for GTP?

A. Its activity would increase because GTP would be bound continually.

B. Its activity would decrease because GDP would be bound continually.

C. Its activity would increase because GDP would be bound continually.

D. Its activity would decrease because GTP would be bound continually.

A. Its activity would increase because GTP would be bound continually.

What is the term for the signaling protein composed of multiple subunits, one of which is activated by the binding of GTP, that links receptors to enzymes or ion channels?

A. G-protein-coupled receptor (GPCR)

B. Heterotrimeric GTP-binding protein (G protein)

C. GPCR kinase (GRK)

D. Regulator of G protein signaling (RGS)

B. Heterotrimeric GTP-binding protein (G protein)

What is "cyclic" about cyclic AMP?

A. The ribose moiety of cAMP is arranged as a ring, rather than in its linear form.

B. cAMP is cyclically produced from ATP, used, then reconverted back to ATP.

C. The phosphate of cAMP links two carbons of the ribose moiety, forming a ring.

D. The adenine group of cAMP contains two rings, instead of just a single ring.

C. The phosphate of cAMP links two carbons of the ribose moiety, forming a ring.

What is the name of the enzyme that phosphorylates target proteins in response to a rise in intracellular cyclic AMP?

A. Phospholipase C-β

B. A-kinase anchoring proteins (AKAPs)

C. Cyclic AMP-dependent protein kinase (PKA)

D. CRE-binding (CREB) protein

C. Cyclic AMP-dependent protein kinase (PKA)

Which of the following alterations to the signaling pathway would lead to increased transcription by the CREB protein? Choose one or more:

A. inhibition of adenylyl cyclase

B. inhibition of GTP hydrolysis

C. inhibition of cAMP breakdown

D. inhibition of entry of PKA into the nucleus

B. inhibition of GTP hydrolysis

C. inhibition of cAMP breakdown

Which of the following would increase phosphorylation of CREB by PKA?

A. blocking binding of the regulatory subunits to the catalytic subunits of PKA

B. blocking ATP binding to the active site of PKA

C. blocking nuclear entry of PKA

D. blocking cAMP binding to the regulatory subunits of PKA

A. blocking binding of the regulatory subunits to the catalytic subunits of PKA

What is the name of the second messenger that is released from a phospholipid in the plasma membrane and diffuses to the ER, where it opens Ca2+-release channels?

A. Ca2+

B. Diacylglycerol

C. Cyclic AMP

D. Inositol 1,4,5-trisphosphate (IP3)

D. Inositol 1,4,5-trisphosphate (IP3)

Which one of the following proteins is an enzyme that is bound to the cytoplasmic surface of the plasma membrane and converts membrane PI(4,5)P2 to diacylglycerol and IP3

A. Regulator of G protein signaling (RGS)

B. Protein kinase C (PKC)

C. IP3-gated Ca2+ release channels

D. Phospholipase C-β (PLCβ)

D. Phospholipase C-β (PLCβ)

Why do you suppose cells use Ca2+ (intracellular concentration 10-7 M) for signaling rather than the more abundant Na+ (intracellular concentration 10-3 M)?

A. Ca2+ does not have other important roles, so it can be reserved for signaling.

B. Low concentrations of ions such as Ca2+ are more readily detected by a cell.

C. At low concentrations, few ions are needed to produce large relative changes.

D. Na+ does not move across the membrane into the cell as quickly as Ca2+ does.

C. At low concentrations, few ions are needed to produce large relative changes.

What is the name of the ubiquitous calcium-binding protein whose interactions with other proteins are governed by changes in intracellular Ca2+ concentration?

A. Calmodulin

B. Ryanodine receptor

C. Protein kinase C (PKC)

D. Ca2+/calmodulin-dependent kinase (CaM-kinase)

A. Calmodulin

What is the name for the cell-surface receptors that, when activated by ligand binding, add phosphates from ATP to tyrosine side chains in their own cytoplasmic domains?

A. Olfactory receptors

B. G-protein-coupled receptors (GPCRs)

C. Nuclear receptors

D. Receptor tyrosine kinases (RTKs)

D. Receptor tyrosine kinases (RTKs)

A single amino acid change in Ras eliminates its ability to hydrolyze GTP, even in the presence of a GTPase-activating protein (GAP). Roughly 30% of human cancers have this change in Ras. You have just identified a small molecule that prevents the dimerization of the receptor tyrosine kinase (RTK) that signals via Ras. Would you expect this molecule to be effective in the treatment of cancers that express this common, mutant form of Ras? Why or why not?

A. Yes, undimerized RTKs would bind mutant Ras and keep it inactive.

B. No, stopping RTK dimerization could block other signaling pathways.

C. Yes, by preventing RTK dimerization, you would stop Ras activation.

D. No, Ras is downstream of RTK and thus would not be affected by it.

D. No, Ras is downstream of RTK and thus would not be affected by it.

The Ras GTPase was first discovered as a gene that plays an important role in transforming normal cells into cancer cells. Although Ras is normally activated by a receptor tyrosine kinase (RTK), in many kinds of cancer the Ras gene has sustained a mutation that makes the Ras protein hyperactive. This mutant Ras activates a MAP kinase module, sending unregulated signals that drive cell proliferation and contribute to tumor formation.What kinds of mutations in the Ras gene could lead to hyperactive Ras?

I Mutations that stimulate Ras to bind the Ras GTPase-activating protein (Ras GAP)

II Mutations that decrease the ability of Ras to hydrolyze GTP

III Mutations that block Ras binding to Ras guanine nucleotide exchange factor (Ras GEF)

A. II and III

B. I and III

C. II

D. I

T/F: In general, the intracellular signaling pathways triggered by receptor tyrosine kinases (RTKs) and G-protein coupled receptors (GPCRs) do not overlap or interact.

False