Cell Bio Test 3

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.
Click the card to flip 👆
1 / 130
Terms in this set (130)
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
Intermediate filaments are found in the cytoplasm and the nucleus
A. True
B. False
A
Keratins, neurofilaments, and vimentins are all categories of intermediate filaments.
Phosphorylation causes disassembly during every mitotic cycle.
A. True
B. False
B
Centrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation.
A. True
B. False
A
You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________________.
(a) MtA is involved in stabilizing microtubules.
(b) MtA binds to GTP-bound tubulin on microtubules.
(c) MtA is important for the interaction of microtubules with the centrosome.
(d) MtA will not bind to purified microtubules in a test tube
b
Consider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules?
(a) Although both filaments can grow from both ends, the growth rate is faster at the plus ends.
(b) Depolymerization initiates at the plus ends of filaments.
(c) Nucleotide hydrolysis promotes depolymerization of filaments.
(d) Free subunits (actin and tubulin) carry nucleoside triphosphates.
b
Which of the following statements is false?
(a) Cytochalasins prevent actin polymerization.
(b) Actin filaments are usually excluded from the cell cortex.
(c) Integrins are transmembrane proteins that can bind to the extracellular matrix.
(d) ARPs can promote the formation of branched actin filaments.
B
Your friend works in a biotech company that has just discovered a drug that seems to promote lamellipodia formation in cells. Which of the following molecules is unlikely to be involved in the pathway that this drug affects?
(a) Rac
(b) ARP
(c) actin
(d) myosin
d
Colchicine
is
not
FDA
approved
but
is
often
used
as
a
medication
to
treat
gout.
It
is
a
natural
toxic
product
and
secondary
metabolite
that
a. Inhibits
actin
polymerization
b. Inhibits
microtubule
polymerization
c. Inhibits
microtubule
depolymerization
d. None
of
the
above
b
Some
Bcl2
family
members
promote
apoptosis
others
inhibit
apoptosis
a. True
b. False
A
87) Mitogens operate by a. Suppressing apoptosis b. By overcoming intracellular braking mechanisms that block progression through cell cycle c. Directly activate Cdks d. Inhibit apoptosis e. None of the aboveBCell growth does not depend on cell cycle regulatory mechanisms a. True b. FalseAEpithelial cells have particularly plentiful extracellular matrix that keeps cells together a. True b. FalseBSomatic and proliferating precursor cells can be kept proliferating indefinitely in culture and retain unrestricted developmental potential a. True b. FalseBBeta subunit of a G protein is not tethered to the plasma membrane by a short lipid tail a. True b. FalseACalcium is released from the endoplasmic reticulum in response to the binding of a. Inositol 1,4,5 trisphosphate b. Inositol 1,3,5 trisphosphate c. Inositol 4,5 bisphosphate d. None of the aboveaThe paracellular space between epithelial cells can be altered by contraction of the actin-‐ myosin in a. Tight Junctions b. Adherens Junctions c. Desmosomes d. Hemidesmosomes e. None of the aboveB66) Which is true regarding the component of the cytoskeleton a. Microtubules are the largest and actin is the smallest in diameter b. Microtubules are the most rigid of all three types c. All three (MTs, IFs, actin) are involved in cargo/protein transport d. All of the above e. A, and Be (only actin and microtubules do cargo transport)Which of the following is not associated with intermediate filaments a. Basal bodies b. Addition to the plus end subtraction from the minus end c. Dynein and kinesin d. All of the abovedContractile rings formed during cell division are assembled and regulated by a. Actin b. Myosin c. Actin and myosin d. Microtubules e. Intermediate filamentscActin is arranged in a 9+2 arrangement in cilia and flagella a. True b. FalsebOrganelles maintain their position in the cytosol with the assistance of a. Intermediate filaments b. Microtubules c. Actin d. Lamin e. None of the abovebGrowth factors stimulate a. Actin polymerization b. Intracellular protein synthesis c. DNA replication d. Apoptosis e. None of the abovebCholera toxin causes diarrhea by a. Keeping the intracellular cAMP levels high b. Activating PKA c. ATP mediated efflux of chloride ions d. All of the abovedWhich of the following marks the "point of no return", from which the cell is destined to either divide or die? a. G1 - S phase checkpoint b. G2 phase c. G2 - M phase transition d. anaphase checkpoint e. all of the aboveA) You have isolated a temperature sensitive yeast mutant. When maintained at the restrictive temperature, all of the yeast cells are arrested at the G1-S phase transition due to single gene mutation. Below are listed five proteins. Which one is least likely to be the protein responsible for the observed phenotype (i.e., arrest at G1-s phase transition)? a. P53 b. Cdc20 c. RB d. P21 e. S cyclinbMaturation Promoting Factor (MPF) refers to the molecule present in the cytosol of unfertilized Xenopus oocytes that is capable of driving multiple cycles of M phase and S phase in vitro. What kind of protein is MPF? a. kinase b. ubiquitin ligase c. transcription factor d. tubulin dimer e. none of the abovebWhich of the following processes requires an intact centriole? a. DNA replication b. Formation of the spindle complex c. Cytokinesis d. Formation of the contractile ring e. Formation of ciliaeWhich of the following refers to the protein complex that gathers and organizes newly replicated DNA into chromosomes? a. gatherin b. cohesion c. condensin d. chromatin e. histone H3cDuring cytokinesis, which of the following motor proteins closes the contractile ring? a. cytosolic dynein b. kinesin 4 c. myosin I d. myosin II e. dynamindApoptosis was discovered in which of the following model organisms? a. Saccharomyces cerevisae b. Ceanorhabditis elegans c. Danio rerio d. Mus musculus e. Homo sapiens sapiensbWhich of the following cell-matrix junctions is formed by cell adhesion molecules that are associated with actin filaments? a) desmosomes d) adherens junctions b) hemidesmosomes e) gap junctions c) focal adhesionsc42) Which of the following is FALSE regarding collagens? a) they are the most abundant proteins in the animal kingdom b) they are formed from two alpha helical proteins bound in a coiled-coil c) subunits are encoded by at least 20 genes d) they are assembled into fibers in the extracellular space e) all of the above are true regarding collagen NOTE: collagens are triple coiled - each repeat unit is composed of three alpha helical polypeptides.bWhich of the following is FALSE regarding actin filaments? a) actin filaments are formed through the polymerization of GTP-bound actin subunits b) most actin subunits in a filament are in contact with 4 other subunits c) polymerization only happens at the plus end of an actin filament d) nucleotide hydrolysis results in dissociation of actin subunits at the minus end of the filament e) all of the above are TRUE regarding actin filamentsaPhotoisomerization of the rhodopsin cofactor, 11-cis retinal, results in which of the following? a) exchange of ATP for ADP-bound Gs, and activation of adenylyl cyclase b) exchange of GTP for GDP-bound Gs, and activation of adenylyl cyclase c) exchange of GTP for GDP-bound Go, and activation of phosphodiesterase d) exchange of GTP for GDP-bound Gt, and activation of phosphodiesterase e) exchange of GTP for GDP-bound Gt, and inhibition of guanylyl cyclase21) Phosphorylation of tyrosine residues on receptor tyrosine kinases results in which of the following events? a) receptor dimerization b) nuclear translocation of the receptor c) recruitment of signaling proteins to the plasma membrane d) accumulation of a soluble second messenger in the cytoplasm e) none of the abovecWhich of the following proteins does NOT participate in calcium homeostasis in the cell. a) sodium-calcium antiporter on the plasma membrane b) sodium-calcium antiporter on the endoplasmic reticulum c) calcium binding proteins in the cytoplasm d) calcium ATPase on the plasma membrane e) calcium ATPase on the smooth endoplasmic reticulumbWhich of the following messenger molecules mediates the ripening of fruit? a) ethylene d) methane b) methylene e) acetylene c) ethaneaHow does the Notch receptor signal to the nucleus a) through Gq b) through MAP kinase c) through the JAK-STAT pathway d) through the PKA pathway e) none of the aboveeNuclear lamins are members of which protein class? a) actin binding proteins b) neurofilament proteins c) microtubule binding proteins d) nuclear pore complex proteins e) intermediate filament proteinseWhich of the following is NOT a microtubule organizing center? a) centriole b) centrosome c) basal body d) spindle pole e) all of the above are microtubule organizing centersaWhich of the following is FALSE regarding tubulin dimers? a) they are composed of alpha and beta subunits b) both the alpha and beta subunits bind ATP c) only the beta subunit can hydrolyze its bound nucleotide d) the beta subunit is always exposed at the plus end of the microtubule e) all of the above are true regarding tubulin dimmersbWhich of the following statements is FALSE? a) microtubules grow fastest from the plus end b) microtubules are composed of 13 "protofilaments" c) microtubules undergo "catastrophe", during which they fray at the minus end d) microtubules are often stabilized by plus end capping proteins e) all of the above are TRUE.c) How does the anti-cancer drug Taxol inhibit cell division? a) it stabilizes microtubules b) it destabilizes microtubules c) it causes actin polymerization in the wrong direction d) it initiates apoptosis e) it disrupts DNAaDuring kinesin movement along a microtubule, which event causes the neck linker to "zipper onto the head domain" (i.e., the "Power Stroke") a) hydrolysis of GTP b) hydrolysis of ATP c) dissociation of ADP d) dissociation of Pi e) exchange of ADP for ATPeWhich of the following is TRUE regarding most kinesin motor proteins? a) they hydrolyze ATP and move toward the plus end of the microtubule b) they hydrolyze ATP and move toward the minus end of the microtubule c) they hydrolyze ATP and move toward the plus end of the actin filament d) they hydrolyze GTP and move toward the plus end of the microtubule e) they hydrolyze GTP and move toward the minus end of the microtubuleaThe organization of the actin cytoskeleton is primarily controlled by which of the following? a) protein kinases b) actin binding proteins c) small GTPases d) transcription factors e) phase of the moonbYour lab is investigating the signaling pathway through which a newly discovered peptide, "Peptide X" signals after a G-protein coupled receptor. You observe that addition of Peptide X to cultured epithelial cells results in the accumulation of IP3 in the cytoplasm. This effect is NOT blocked by pertussis toxin. Which of the following G proteins is most likely responsible for Peptide X signaling in epithelial cells? a) Gs d) Gq b) Gi e) Gt c) Goc (but why is it not Gq?)The substance in the cytoplasm of M-phase cells that promotes mitosis in cell-free extracts of Xenopus oocytes was originally called ... a. Momma's Powerful Force b. Maternal Procreation Factor c. Mammalian Prometaphase Factor d. Maturation Promoting Factor e. None of the aboveD2. MPF activity is attributed to which of the following proteins? a. cyclin dependent kinase 1 (Cdk1) b. cyclin dependent kinase 2 (Cdk2) c. cyclin A d. cyclin B e. MPF is not a proteinaHow do survival factors prevent apoptosis? a. decreased synthesis of caspases b. increased degradation of caspases c. direct inhibition of caspases d. induction of Bcl-2 protein e. all of the abovedWhich of the following events usually terminates muscle contraction? a. ATP levels are exhausted b. calcium ions are transported back into the sarcoplasmic reticulum c. myosin head groups are phosphorylated by myosin light chain kinase d. acetylcholine is degraded by acetylcholine esterase e. sodium channels inactivatebWhich of the following toxins binds to and stabilizes microtubules? a. cytochalasin B b. taxol c. colchicine d. phalloidin e. vinblastinbWhich of the following toxins binds to and stabilizes actin filaments? a. cytochalasin B b. taxol c. colchicine d. phalloidin e. vinblastindDuring which phase of the cell cycle does most cell growth occur? a. G1 phase b. S phase c. G2 phase d. M phase e. cell growth occurs throughout the cell cycleaCholera toxin disrupts cell biochemistry by covalently modifying the alpha subunit of which of the following trimeric G proteins? a. Gs d. Gq b. Gi e. none of the above c. GoaWhich of the following is false regarding protein kinase A? a. it is activated by the binding of cAMP to the catalytic subunit b. it phosphorylates and activates the CREB protein c. it mediates the effects of G-protein coupled receptors that signal through Gs d. it is a serine-threonine kinase e. all of the above are true about protein kinase AaG-protein receptor kinases (GRKs) phosphorylate GPCRs at multiple sites, marking them for desensitization. Which of the following proteins binds to phosphorylated GPRCs resulting in receptor desensitization? a. adaptin d. sequestin b receptin e. inactin c. arrestincDuring the G-protein activation cycle, a ligand-bound GPCR behaves like which of the following? a. a protein kinase b. a protein phosphatase c. a guanine nucleotide exchange factor d. a GTPase activating factor e. a nuclear localization signalaThe mitogen activated protein (MAP) kinase cascade is activated by which of the following? a. RTKs that signal through Ras b. RTKs that signal through PI-3 Kinase c. GPCRs that signal through Gs d. GPCRs that signal through Ras e. none of the aboveaWhich of the following events occurs during signaling through cytokine receptors? a. the Ras oncogene activates the MAPK cascade b. a gene regulatory protein is produced by selective proteolysis c. Janus kinases (JAKs) phosphorylate STAT proteins d. cyclic GMP is hydrolyzed to 5'-GMP e. !-catenin accumulates and enters the nucleuscWhich of the following is an intermediate filament protein found exclusively in epithelial cells? a. keratin b. collagen c. vimentin d. lamin A e. none of the above 26. Which of the following is an intermediate filament protein found in all cells? a. keratin b. collagen c. vimentin d. lamin A e. none of the abovea , dWhat is the function of the centrioles? a. they sense the earth's magnetic field b. they nucleate microtubules c. they bind to the Golgi apparatus d. they are essential for mitosis e. their function is not knowneWhich of the following cytoskeletal components derives strength from coiled-coil domains between dimeric subunits? a. microtubules b. actin c. intermediate filaments d. all of the abovecIn the tubulin heterodimer, the B-tubulin molecule provides which of the following? a. the exchangeable ATP binding site b. the non-hydrolyzable ATP binding site c. the exchangeable GTP binding site d. the non-exchangeable GTP binding sitecHow many doublet microtubules are in an axoneme (e.g., flagellum) a. 8 d. 13 b. 9 e. 15 c. 11bWhen does treadmilling of actin filaments occur? a. when the rate of ATP hydrolysis exceeds the rate of actin polymerization b. when the rates of actin polymerization at the plus (+) and minus (-) ends of the actin filament are equal. c. when the rate of actin polymerization at the plus (+) end of the actin filament is equal to the rate of actin depolymerization at the minus (-) end of the actin filament. d. when the rates of actin depolymerization at the plus (+) and minus (-) ends of the actin filament are equal. e. when myosin motors are pulling against actin filaments.cWhich of the following actin accessory proteins binds to and destabilizes actin filaments? a. formin d. cofilin b. filamin e. fimbrin c. profilindWhich of the following is false regarding dynein motors? a. most are cytoplasmic proteins b. they move toward the plus (+) end of microtubules c. they are ATPases d. the cytoplasmic forms are homodimers e. all of the above are true regarding dynein motorsb41. What prevents pre-mature (involuntary) contraction of striated muscle? a. lack of ATP b. lack of calcium c. myosin light chain kinase d. myosin binding sites are blocked by tropomyosin e. myosin binding sites are blocked by troponin complex 42. What is the role of the troponin complex in striated muscle contraction? a. activates myosin light chain kinase b. blocks myosin binding sites on actin filaments c. transmits action potentials to myofibrils d. opens calcium channels on the sarcoplasmic reticulum e. binds calcium and releases tropomyosind, eWhich structure is responsible for transmitting the action potential to calcium storage sites in striated muscle cells? a. sarcoplasmic reticulum b. intermediate filaments c. actin filaments d. transverse tubule e. desmosomesdIn the 1980s, cell biologists identified a cytoplasmic component of fertilized frog oocytes that was capable of inducing mitosis in unfertilized oocytes. During early frog development, the activity of this substance, referred to as the "maturation promoting factor", peaked during M phase of each cleavage event. What is "maturation promoting factor"? a. Cyclin B b. Cdk2 c. M-Cdk d. S-Cdk e. Anaphase Promoting Complex (APC)c8. Exposure of cultured fibroblasts to a non-lethal dose of X-rays would most likely arrest these cells in which phase of the cell cycle? a. G1 phase b. S phase c. G2 phase d. M phase e. all phases 9. A serious error of DNA replication would most likely arrest cells in which phase of the cell cycle? a. G1 phase b. S phase c. G2 phase d. M phase e. all phasesa , cMost mitogens, growth factors and survival factors signal through ... a. G-protein linked receptors b. cyclic AMP c. cytoplasmic receptors d. receptor tyrosine kinases e. all of the abovedSignal induced changes in the architecture of the actin cytoskeleton are mediated by members of the Rho family of small GTPases. Which Rho family member facilitates the formation of stress fibers? a. Rho b. Ras c. Rac d. Rab5 e. Cdc42a (-rho: stress fibers -rac: actin cytoskeleton migrates to and remains in cell cortex)S cyclin proteins begin to accumulate during G1 phase. When does the concentration of S cyclin protein fall? a. G1 phase b. S phase c. G2 phase d. early M phase (mitosis) e. late M phase (cytokinesis)d (do we have to know this?)Organelles maintain their position in the cytosol with the assistance of a. Intermediate filaments b. Microtubules c. Actin d. Lamin e. None of the abovebContractile rings formed during cell division are assembled and regulated by a. Actin b. Myosin c. Actin and myosin d. Microtubules e. Intermediate filamentscWhen colchicines is added to the cell, the following will occur a. Microtubules will grow at a faster rate b. Microtubules will shrink at a faster rate c. It will function as a mitotic poison or spindle poison d. B and C e. A and CdMutations in the protein plectin, the cross-‐linking accessory protein in the intermediate filaments can cause the human diseases a. Epidermolysis bullosa simplex b. Muscular dystrophy c. Listeria d. Parkinsons disease e. A and BeWhich is true regarding the component of the cytoskeleton a. Microtubules are the largest and actin is the smallest in diameter b. Microtubules are the most rigid of all three types c. All three (MTs, IFs, actin) are involved in cargo/protein transport d. All of the above e. A, and BeWhich of the following statements is TRUE a. Serine/threonine protein kinases phosphorylate extracellular proteins on serines and/or threonines b. Tyrosine kinases phosphorylate intracellular proteins on tyrosines c. Serine/threonine kinases phosphorylate intracellular proteins in serines and/or threonines d. A and B e. B and C a. All of the aboveeThe concentration of free calcium in the cytosol of an unstimulated cell is kept high compared with its concentration in both the extracellular fluid and the endoplasmic reticulum a. True b. FalsebThe concentration of actin monomers is high in the cytosol but actin filaments are not assembled spontaneously because the actin monomers are sequestered by thymosin beta4 a. True b. FalseaThe concentration of actin monomers is high in the cytosol but actin filaments are not assembled spontaneously because the actin monomers are sequestered by thymosin beta4 a. True b. FalseaThe disassembly of nuclear envelope depends on a. Phosphorylation of nuclear lamins and nuclear pore proteins b. Dephosphorylation of both nuclear lamins and nuclear pore proteins c. Dephosphorylation of M cyclin d. Phosphorylation of M cyclinaPhospholipase C can be activated by a. G protein coupled receptors b. Receptor tyrosine kinases c. A and BcHydrolysis of ATP to ADP decreases the strength of binding between monomers in a microfilament a. True b. FalseaThis cell surface structure functions as a chemosensor to regulate direction of cell migration a. Lamellipodia b. Filopodia c. Membrane ruffles d. None of the abovebThere is a profound similarity between microtubules and microfilaments (actin filaments) a. Both are polymerized and depolymerized b. Both have polarity a plus and a minus end c. Both are associated with motor proteins d. Both undergo dynamic instability e. A, B and CeCholera toxin causes diarrhea by a. Keeping the intracellular cAMP levels high b. Activating PKA c. ATP mediated efflux of chloride ions d. All of the aboved21. Activation of phospholipase C-" results in the production of two signaling molecules. Which signaling molecule is responsible for the release of calcium from the smooth ER? a. inositol 3,4,5 trisphosphate b. inositol 2,4,5 trisphosphate c. inositol 1,4,5 trisphosphate d. diacylglycerol e. none of the above 22. Calcium homeostasis is maintained, in part, through the action of calcium ATPases. These P-type pumps can be found on which of the following membranes? a. plasma membrane b. mitochondrial inner membrane c. smooth ER d. two of the above e. all of the abovec, dWhat is the role of arrestins in G-protein coupled receptor signaling? a. they prevent receptor dimerization b. they are guanine nucleotide exchange factors c. they are protein kinases that phosphorylate GPCRs d. they couple receptors to G proteins e. they participate in receptor desensitizationeUnder conditions that support treadmilling of actin filaments, what would be the consequence of capping the actin filaments at the plus (+) end? a. catastrophe b. increased cell motility c. rapid polymerization of actin filaments d. rapid depolymerization of actin filaments e. none of the abovedIn neutrophils, the polarization of the actin cytoskeleton leading to cell motility is triggered by which of the following events? a. assembly of actin filaments b. assembly of microtubules c. activation of cell surface receptors by extracellular messengers d. activation of signaling cascades by intracellular messengers e. gene expressioncWhen does treadmilling of actin filaments occur? a. when the rates of actin polymerization at the plus (+) and minus (-) ends of the actin filament are equal. b. when the rate of actin polymerization at the plus (+) end of the actin filament is equal to the rate of actin depolymerization at the minus (-) end of the actin filament. c. when the rates of actin depolymerization at the plus (+) and minus (-) ends of the actin filament are equal. d. when myosin motors are pulling against actin filaments. e. when the rate of ATP hydrolysis exceeds the rate of actin polymerizationDuring which phase of the cell cycle does most cell growth occur? a. G1 phase b. S phase c. G2 phase d. M phase e. cell growth occurs throughout the cell cyclea19. Which of the following signaling enzymes creates sites on the plasma membrane for the recruitment and activation of protein kinase C? a. PI3 kinase b. GRK kinase c. adenylyl cyclase d. guanylyl cyclase e. phospholipase C 20. Receptor tyrosine kinases (RTKs) that signal through PI-3 kinase, create binding sites on the plasma membrane for the recruitment and activation of downstream kinases that contain which of the following? a. PTB domains b. ATP binding domains c. pleckstrin homology (PH) domains d. SRC homology 2 (SH2) domains e. SRC homology 3 (SH3) domainse, c8. Exposure of cultured fibroblasts to a non-lethal dose of X-rays would most likely arrest these cells in which phase of the cell cycle? a. G1 phase b. S phase c. G2 phase d. M phase e. all phases 9. A serious error of DNA replication would most likely arrest cells in which phase of the cell cycle? a. G1 phase b. S phase c. G2 phase d. M phase e. all phasesa, cAs you know, the alkaloid, colchicine, promotes depolymerization of microtubules. Treatment of early frog embryos with colchicine would most likely arrest cells at which phase of the cell cycle? a. G1 phase b. S phase c. G2 phase d. M phase e. G2-M checkpointdWhich of the following is FALSE regarding the actin cytoskeleton a. it is the most dynamic component of the cytoskeleton b. it consists of polarized filaments comprised of helical polymers of actin subunits c. actin filaments grow at the (+) end and shrink at the (-) end d. the affinity of actin subunits for an actin filament is determined by the state of the bound adenine nucleotide e. all of the above are truee5. Which motor protein extends new channels of the endoplasmic reticulum into the cytosol? a. kinesins b. myosin I c. myosin II d. dyneins e. none of the above 6. What is the doublet : singlet ratio of the microtubule complex ("axoneme") that supports the flagella and cilia? a. 9 : 1 d. 6 : 2 b. 4 : 1 e. 9 : 3 c. 9 : 2a, cAt the trailing edge of a motile cell, what process drives the movement of cell organelles toward the lamelipodium? a. formation of focal adhesions b. capping of actin filaments at the plus (+) end c. myosin II movement along the actin cytoskeleton d. nucleation of new polymerization sites by ARPs e. none of the abovecDuring myosin II movement along an actin filament, which event leads to dissociation of a myosin head domain from the actin filament? a. binding of ATP b. hydrolysis of ATP c. dissociation of Pi d. dissociation of ADP e. dissociation of ATPaWhich of the following is FALSE regarding the troponin-tropomyosin complex? a. it is responsible for triggering contraction of skeletal muscle b. the tropomyosin component interacts with actin binding sites on myosin head domains c. it changes conformation rapidly in response to increased cytosolic calcium ions d. calcium ions bind to the troponin component e. all of the above are truebWhich of the following is/are NOT DNA binding protein(s)? a. JAKs b. CREB c. STATs d. SMADs e. none of the above are DNA binding proteinsaWhich of the following is FALSE regarding intermediate filaments a. keratin is an intermediate filament b. they are encoded by many genes c. they bind and hydrolyze GTP d. they are strengthened by coiled-coil interactions e. all of the above are truecWhich of the following structures shorten during muscle contraction? (a) myosin filaments (b) flagella (c) sarcomeres (d) actin filamentscFigure Q17-52 shows the leading edge of a lamellipodium. Which of the following statements is false? Figure Q17-52 (a) Nucleation of new filaments near the leading edge pushes the plasma membrane forward. (b) ARP proteins nucleate the branched actin filaments in the lamellipodium. (c) Capping proteins bind to the minus end of actin filaments. (d) There is more ATP-bound actin at the leading edge than in the actin filaments away from the leading edge.cThis cell surface structure functions as a chemosensor to regulate direction of cell migration a. Lamellipodia b. Filopodia c. Membrane ruffles d. None of the abovebThe drug taxol binds tightly to microtubules and prevents them from depolymerizing. The drug colchicines tightly binds to free tubulin and prevents its polymerization into microtubules. Which of these drugs arrests dividing cells in mitosis a. Taxol b. Colchicines c. BothcContractions in smooth muscle cells depend on which of the following activation steps a. Calcium activated phosphorylation of myosin II b. Calcium binding to troponin c. GTP binding to myosin II d. Actin polymerizationaMatch the class of cell-surface receptor with the best description of its function. Not all descriptors will be used. enzyme-coupled receptors ______ a. alter the membrane potential directly by changing the permeability of the plasma membrane b. signal by opening and closing in a ligand-independent manner c. must be coupled with intracellular monomeric GTP-binding proteins d. all receptors of this class are polypeptides with seven transmembrane domains e. discovered for their role in responding to growth factors in animal cellseWhich of the following statements about G-protein-coupled receptors (GPCRs) is false? (a) GPCRs are the largest family of cell-surface receptors in humans. (b) GPCRs are used in endocrine, paracrine, and neuronal signaling. (c) GPCRs are found in yeast, mice, and humans. (d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.dA protein kinase can act as an integrating device in signaling if it ___________________. (a) phosphorylates more than one substrate. (b) catalyzes its own phosphorylation. (c) is activated by two or more proteins in different signaling pathways. (d) initiates a phosphorylation cascade involving two or more protein kinases.cWhich of the following statements is false? (a) Cytochalasins prevent actin polymerization. (b) Actin filaments are usually excluded from the cell cortex. (c) Integrins are transmembrane proteins that can bind to the extracellular matrix. (d) ARPs can promote the formation of branched actin filaments.bConsider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules? (a) Although both filaments can grow from both ends, the growth rate is faster at the plus ends. (b) Depolymerization initiates at the plus ends of filaments. (c) Nucleotide hydrolysis promotes depolymerization of filaments. (d) Free subunits (actin and tubulin) carry nucleoside triphosphates.bYou discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________________. (a) MtA is involved in stabilizing microtubules. (b) MtA binds to GTP-bound tubulin on microtubules. (c) MtA is important for the interaction of microtubules with the centrosome. (d) MtA will not bind to purified microtubules in a test tubebCentrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation. A. True B. FalseaIntermediate filaments help protect animal cells from mechanical stress because ____________. (a) filaments directly extend from the interior of the cell to the extracellular space and into the next cell, linking one cell to the next, helping to distribute locally applied forces. (b) filaments in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells. (c) filaments remain independent of other cytoskeletal elements and keep the mechanical stress away from other cellular components. (d) filaments make up the desmosome junctions that connect cells; these junctions are more important than the internal network of filaments for protecting cells against mechanical stress.bIntermediate filaments are found in the cytoplasm and the nucleus A. True B. FalseaWhich 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.Keratins are found in a. Hair b. Feathers c. Tongue d. All of the abovedPhospholipase C can be activated by a. G protein coupled receptors b. Receptor tyrosine kinases c. A and BcHydrolysis of ATP to ADP decreases the strength of binding between monomers in a microfilament a. True b. FalseaWhat are T-tubules? a) components of the sarcoplasmic reticulum b) extensions of the muscle cell plasma membrane c) triplet microtubules found in the centriole and basal bodies d) modified endoplasmic reticulum e) none of the abovebEpidermolysis Bullosa Simplex is due to a mutation in which of the following proteins? a) an intermediate filament protein b) an actin binding protein c) a protein kinase d) a G-protein e) none of the aboveaNicotine is one of the most addictive substances known. How does nicotine exert its physiological effects in humans? a) it stimulates the release of acetylcholine from cholinergic nerve terminals b) it blocks the synthesis of acetylcholine in cholinergic nerve terminals c) it inhibits the degradation of acetylcholine at cholinergic synapses d) it acts as an antagonist on acetylcholine receptors e) it acts as an agonist on acetylcholine receptorseWhich of the following is not an example of a connective tissue? (a) bone (b) the layer of photoreceptors in the eye (c) the jellylike interior of an eye (d) cartilagebAll intermediate filaments are of similar diameter because ____________. (a) the central rod domains are similar in size and amino acid sequence. (b) the globular domains are similar in size and amino acid sequence. (c) covalent bonds among tetramers allow them to pack together in a similar fashion. (d) there is only a single type of intermediate filament in every organism.a