Cell Bio Unit 4

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 diagrammed in Figure Q16-32), which decreases the cell's excitability by making it harder to depolarize the plasma membrane. Indicate whether each of the following conditions would increase or decrease 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

decrease increase decrease decrease decrease

The down regulations of receptors can occur by_____ a. alternations to the receptor that results in a lower binding affinity for its downstream large. b. alternations to the receptors that recent it from initiating changes in cellular response or function c. removal of the receptor from cell surface d. receptor mediated endocytosis e. all of the above

e. all of the aove

A protein kinase can_______________. a. be the receptor for a hormone b. convert ATP to cAMP c. directly activate G proteins d. decrease the cytosolic calcium level e. be inhibited by a phosphorylation by other proteins

e. be inhibited by a phosphorylation by other proteins

Tau is a non motor MAP that is important in ___ a. cell division b. actin polymerization c.actin cross linking d. muscle contraction e. microtubule crosslinking

e. microtubule crosslinking

In a typical cell, calcuim ions ____ a. bind to calmodulin and inactivate it b. often concentrated within the nucleus c. are not widely used as second messengers d. are concentrated wihtin the cytosol e. none of the above

e. none of the above

SH2 domain containing proteins bind to which of teh following proteins? a. phospholipase b. MAP kinase c. Ras d. Myc e. tyrosine kinase receptor

e. tyrosine kinase receptor

Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely __________________ concentration of free Ca2+ in the cytosol, compared with its concentration in the __________________ space and in the __________________, creating a steep electrochemical gradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as __________________, which also binds diacylglycerol, and __________________, which activates CaM-kinases. adenylyl cyclase endoplasmic reticulum nuclear average extracellular peroxisome Ca2+ high phospholipase C calmodulin intracellular protein kinase A colorful low protein kinase C

low extracellular ER Protein Kinase C Calmodulin

Rank the following cytoskeletal filaments from smallest to largest in diameter (1 = smallest in diameter, 4 = largest) ______ intermediate filaments ______ microtubules ______ actin filament ______ myofibril

__2___ intermediate filaments (10 nm diameter) __3___ microtubules (25 nm) __1___ actin filament (5-9 nm) __4___ myofibril (1-2 μm

Proteins belonging to the ________ family of GTPases regulate changes in the actin cytoskeleton in response to extracellular signals. (a) Rho (b) Ras (c) Ran (d) Rab

a) Rho

Depolarization of smooth muscle cells induces prolonged Calcium increase. (a) True (b) False

a) True

The receptor for epidermal growth factor is a typical receptor tyrosine kunase. It does NOT___ a. aggregate and undergo autophosphorylation b. bind to proteins with SH2 domains c. doesnt not respond to endocrine signlas d. resoind to ligand e. have a cytosolic domain

c. doesnt not respond to endocrine signlas

Tyrosine kinase receptor can activate the enzyme P13K , which phosphorylated inositol phospholipids. These phospholipids then: a. serves as phosphate donors in phosphorylation reactions b. activates Ras c. serves as docking sites that recruit intracellular PH domain contain signaling proteins to the plasma membrane d. activates G proteins

c. serves as docking sites that recruit intracellular PH domain contain signaling proteins to the plasma membrane

There are many actin binding protein in cells that can bind to actin and modify its activity. some protein such as ____ bind to actin monomers sequestering them until needed for filament formation a.stathmin b. profilin c. thymosin d. WASP

c. thymosin

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 neuronal signaling paracrine signaling endocrine signaling

The enzyme cyclic AMP phosphodiesterase helps terminate a response mediated by an increase in cyclic AMP by: a.converting AMP to cyclic AMP b.converting cyclic AMP to ATP c. converting ATP to cyclic AMP d. converting cyclic AMP to AMP

converting cyclic AMP to AMP.

Which of the following statements regarding dynamic instability is false? (a) Each microtubule filament grows and shrinks independently of its neighbors. (b) The GTP cap helps protect a growing microtubule from depolymerization. (c) GTP hydrolysis by the tubulin dimer promotes microtubule shrinking. (d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.

d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.

The following proteins are important for cell movement. Match the following proteins with their function. myosin _____ A. nucleation of new actin filaments at the side of an existing filament ARP proteins _____ B. regulation of the availability of actin monomers profilin _____ C. important for the growth of straight, unbranched actin filaments integrins _____ D. contracting the rear of the cell formins _____ E. involvement in focal contacts

myosin ___D_____ ARP proteins ___A_____ profilin ___B_____ integrins ___E_____ formins ___C_____

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. Explain your answers. A. An extracellular signaling molecule binds and activates a GPCR. B. The activated GPCRs cause Gα to separate from Gβ and Gγ. C. Adenylyl cyclase produces cyclic AMP. D. cAMP activates protein kinase A. E. Protein kinase A phosphorylates target proteins.

no yes yes no yes

A researcher extracts the cytosol and cytoskeletal components out of the cell and places the mixture into a tube. What result do you expect if the researcher adds a non-hydrolyzable GTP analog to the mixture in vitro? (a). Destabilization of all polymerized microtubules present in the tube (b). destabilization of all polymerized microfilaments present in the tube (c). overstabilization of all polymerized microfilaments present in the tube (d). overstabilization of all polymerized microtubules present in the tube (e). no effect

d). overstabilization of all polymerized microtubules present in the tube

When unstimulated , the Ga subunit is bound to ____ a. aldenylyl b. potassuim channel c. Ras d. GBy

d. GBy

GPCRs are often referred to as seven-pass transmembrane receptors because they have: a. seven pores that signal molecules can use to pass through the bilayer b. seven receptor on each side of the lipid bilayer that receives and transmit signals. c. seven different G proteins with which they interact to amplify signals d. a polypeptide chain that crosses the lipid bilayer seven times.

d. a polypeptide chain that crosses the lipid bilayer seven times.

Cyclic AMP is ____ a. allosteric regulator of Ga b. allosteric reguator of phosphodiesterase c. allosteric regulator of protein kinase B d. product of adenylyl cyclase e. allosteric reglulator of phospholipase C

d. product of adenylyl cyclase

The receptor for epidermal growth factor (EGF) is a typical receptor tyrosine kinase. Therefore, it does NOT ________. (a). aggregate and undergo autophosphorylation (b). bind to proteins with SH2 domains (c). activate hetero-trimeric G proteins (d). respond to ligand (e). have a cytosolic domain

(c). activate hetero-trimeric G proteins

Local mediators ________. (a). include androgens and estrogens (b). include epinephrine and norepinephrine (c). include EGF (d). are stable for long periods (e). act over large distances

(c). include EGF

Paracrine hormones ________. (a). include androgens and estrogens (b). include epinephrine and norepinephrine (c). are stable for long periods (d). act locally (e). act over large distances

(d). act locally

Ring-shaped complexes of γ-tubulin serve to ________ in the centrosome. (a). depolymerize microfilaments (b). depolymerize microtubules (c). protect microfilaments (d). nucleate assembly of microtubules (e). stabilize microfilaments

(d). nucleate assembly of microtubules

When unstimulated, the Gα subunit is bound to ____. (a) Adenylyl Cyclase (b) Potassium Channel (c) Ras (d) GPCR (e) None of the above

(e) None of the above

Which of the following statements is true? (a) MAP kinase is important for phosphorylating MAP kinase kinase. (b) PI 3-kinase phosphorylates IP3. (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. (e) None of the above.

(e) None of the above.

Rho family proteins regulate polymerization of ________ into ________ in microfilament production. (a). F-actin, G-actin (b). keratin, intermediate filaments (c). tubulin, microtubules (d). tubulin, intermediate filaments (e). G-actin, F-actin

(e). G-actin, F-actin

The binding of ________ to endothelial cells triggers the production of ________, which leads to muscle relaxation. (a). histamine; nitric oxide (b). acetylcholine; calcium (c). somatotropin; growth factors (d). histamine; calcium (e). acetylcholine; nitric oxide

(e). acetylcholine; nitric oxide

A protein kinase can ________. (a). be the receptor for a hormone (b). convert ATP to cAMP (c). directly activate G proteins (d). decrease the cytosolic calcium level (e). be phosphorylated by other proteins

(e). be phosphorylated by other proteins

Phospholipase C cleaves PIP2 into ________ and ________. (a). PIP and phosphate (b). MAP kinase and cAMP (c). PKC and DAG (d). Ca++ and calmodulin (e). diacylglycerol and inositol trisphosphate

(e). diacylglycerol and inositol trisphosphate

Tyrosine-kinase receptors ____. (a). bind to nonpolar signal molecules such as NO and steroids (b). enzymatically hydrolyze the signal molecule shortly after its arrival (c). enzymatically degrade GTP to GDP (d). directly allow specific ions to enter the cell after ligand binding (e). send signals though recruiting SH2 domain proteins

(e). send signals though recruiting SH2 domain proteins

Movement of nonmuscle cells involves all of the following steps EXCEPT ________. (a). protrusion (b). detachment (c). attachment (d). contraction (e). transcytosis

(e). transcytosis

Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments? (a) Actin filaments would grow longer. (b) Actin filaments would grow shorter because depolymerization would be enhanced. (c) Actin filaments would grow shorter because new monomers could not be added to the filaments. (d) No change, as addition of monomers binding nonhydrolyzable ATP would not affect actin filament length.

(a) Actin filaments would grow longer.

Which 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.

___________ proteins are important for the formation of unbranched actin filaments commonly found in filopodia. (a) Formin (b) γ-TuRC (c) ERM (d) ARP

(a) Formin

Which of the following statements about the function of the centrosome is false? (a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome. (b) Centrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation. (c) Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules. (d) Centrosomes are the major microtubule-organizing center in animal cells.

(a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

Which of the following statements about microtubules is true? (a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. (b) The centromere nucleates the microtubules of the mitotic spindle. (c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. (d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.

(a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.

Which 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.

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? (a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive (b) addition of a drug that prevents GTP hydrolysis by Gα (c) addition of a drug that activates adenylyl cyclase (d) addition of a drug that mimics the ligand of ERC1

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

Which of the situations below will enhance microtubule shrinkage? (a) addition of a drug that inhibits GTP exchange on free tubulin dimers (b) addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers (c) addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules (d) addition of a drug that blocks the ability of a tubulin dimer to bind to γ-tubulin

(a) addition of a drug that inhibits GTP exchange on free tubulin dimers

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

Which of the following items is not important for flagellar movement? (a) sarcoplasmic reticulum (b) ATP (c) dynein (d) microtubules

(a) sarcoplasmic reticulum

All 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) the central rod domains are similar in size and amino acid sequence

During G-protein activation, ________ binds ________, thus become activated. (a). Gα; GTP (b). Gβ; GTP (c). Gα; ATP (d). Gβ; GDP (e). Gα; GDP

(a). Gα; GTP

During Ras activation, ________ binds ________. (a). Ras; GTP (b). RasGEF; ATP (c). RasGEF; GDP (d). RasGap;GTP

(a). Ras; GTP

In a typical cell, calcium ions ________. (a). bind to calmodulin and activate it (b). are often concentrated within the nucleus (c). are not very widely used as second messengers (d). are concentrated within the cytosol (e). none of the above

(a). bind to calmodulin and activate it

G protein-linked receptors interact with G proteins________. (a). with the G protein binding domain adjacent to the cytosol-exposed segment between two sets of helices (b). with the G protein binding domain directly adjacent to the ligand-binding site when the receptor binds GTP (c). with the membrane spanning region of the receptor most distant from the ligand-binding α-helices (d). with the membrane-spanning region of the G protein adjacent to the ligand-binding α-helices

(a). with the G protein binding domain adjacent to the cytosol-exposed segment between two sets of helices

Figure shown below describes 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 inhibits 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

(a)addition of a drug that inhibits Ras

The _________ proteins are important for nucleation of the branched actin structures commonly found in the lamellipodia of moving cells. (a) γ-TuRC (b) ARP (c) ERM (d) Formin

(b) ARP

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) Actin filaments are usually excluded from the cell cortex.

______ proteins bind to the end of actin filaments. (a) cofilin (b) CapZ (c) tropomyosin (d) filamin (e) α-actinin

(b) CapZ

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) Depolymerization initiates at the plus ends of filaments.

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.

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 diagrammed in the Figure below. Which of the following statements is true? Picture (a) In the absence 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 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.

(b) In the absence of survival signal, Bad inhibits the cell death inhibitor Bcl2

Cytokine receptors have no intrinsic enzyme activity but are associated with cytoplasmic tyrosine kinases called ______, which become activated on the binding of cytokine to its receptor and go on to phosphorylate and activate cytoplasmic transcriptional regulators called STATs. (a)PI3K (b) JAKs (c) PTEN (d) MAPK

(b) JAKs

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) MtA binds to GTP-bound tubulin on microtubules.

Which of the following statements about organellar movement in the cell is false? (a) Organelles undergo saltatory movement in the cell. (b) Only the microtubule cytoskeleton is involved in organellar movement. (c) Motor proteins involved in organellar movement use ATP hydrolysis for energy. (d) Organelles are attached to the tail domain of motor proteins.

(b) Only the microtubule cytoskeleton is involved in organellar movement.

Which of the following statements about skeletal muscle contraction is false? (a) When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane. (b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction. (c) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. (d) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.

(b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction

Which of the following statements is true? (a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. (b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling. (c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. (d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells

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

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) 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 conditions is likely to decrease the likelihood of skeletal muscle contraction? (a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero (b) addition of a drug that blocks Ca2+ binding to troponin (c) an increase in the amount of ATP in the cell (d) a mutation in tropomyosin that decreases its affinity for the actin filament

(b) addition of a drug that blocks Ca2+ binding to troponin

Figure shown below describes 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 stimulates Ras (b) addition of a drug that decreases 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

(b) addition of a drug that decreases the affinity of protein Y and Ras

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________. (a) activate the RTK. (b) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane. (c) directly phosphorylate Akt. (d) to create DAG

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

Intermediate 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.

(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.

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________. (a) neurotransmitter. (b) hormone. (c) dissolved gas. (d) scaffold.

(b) hormone.

When a GPCR binds an extracellular signal, an intracellular G protein, composed of _____ subunits, becomes activated. (a) two (b) three (c) four (d) seven

(b) three

In a typical cell, calcium ions ________. (a). bind to calmodulin and inactivate it (b). are often concentrated within the endoplasmic reticulum (c). are not very widely used as second messengers (d). are concentrated within the cytosol (e). all of the above

(b). are often concentrated within the endoplasmic reticulum (

MAPs regulate the ________. (a). assembly of microfilaments (b). assembly of microtubules (c). synthesis of kinesin (d). synthesis of dynein (e). assembly of intermediate filaments

(b). assembly of microtubules

Stimulation of a muscle cell by a nerve impulse causes all of the following responses EXCEPT ________. (a). release of neurotransmitter at the neuromuscular junction (b). calcium pumping into the sarcoplasmic reticulum (c). depolarization of the muscle cell

(b). calcium pumping into the sarcoplasmic reticulum

You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Which of the following statements is most likely to be true? (a) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more unbranched actin filaments than normal cells. (b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells. (c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells. (d) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells.

(c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells.

Which of the following statements about the cytoskeleton is false? (a) The cytoskeleton is made up of three types of protein filaments. (b) The cytoskeleton controls the location of organelles in eukaryotic cells. (c) Covalent bonds between protein monomers hold together cytoskeletal filaments. (d) The cytoskeleton of a cell can change in response to the environment

(c) Covalent bonds between protein monomers hold together cytoskeletal filaments.

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 diagrammed in the Figure below. Which of the following statements is true? Picture (a) In the absence of a survival signal, Akt localizes to the plasma membrane by binding to PIP3. (b) In the absence of survival signal, Bad inhibits apoptosis. (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. (e) None of the above.

(c) In the presence of survival signal, the cell death inhibitory protein Bcl2 is active.

You are studying nuclear lamins in yeast. Using recombinant DNA technology, you alter the coding sequence of a nuclear lamin gene such that the gene now codes for a nuclear lamin protein that can no longer be phosphorylated when the nuclear envelope is broken down during mitosis. What do you predict would happen if the yeast cell only had the altered nuclear lamin gene (and not the unaltered version)? (a) Mitosis should proceed as usual because the dephosphorylation of the lamin is what is important for nuclear lamina assembly during mitosis, so phosphorylation will not be necessary. (b) Disassembly of the nuclear lamins will occur prematurely because the lamins cannot be phosphorylated. (c) Nuclear lamins will no longer disassemble properly during mitosis. (d) Nuclear lamins will be unable to produce dimers, as coiled-coil formation will be disrupted.

(c) Nuclear lamins will no longer disassemble properly during mitosis

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 muscle cells, 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 QGF.

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

The following happens when a G-protein-coupled receptor activates a G protein. (a) The β subunit exchanges its bound GDP for GTP. (b) The GDP bound to the α subunit is phosphorylated to form bound GTP. (c) The α subunit exchanges its bound GDP for GTP. (d) It activates the α subunit and inactivates the βγ complex

(c) The α subunit exchanges its bound GDP for GTP.

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 local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________. (a) activating a G protein. (b) activating a receptor tyrosine kinase. (c) diffusing into cells and stimulating the cyclase directly. (d) activating an intracellular protein kinase.

(c) diffusing into cells and stimulating the cyclase directly.

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____. (a) killing cells immediately, exerting their physiological effects by causing cell death. (b) diffusing through cell plasma membranes and binding to transcription factors to change gene expression. (c) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus. (d) removing cell-surface receptors from the plasma membrane

(c) 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 ___________________. (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.

(c) is activated by two or more proteins in different signaling pathways

Which of the following statements is correct? Kinesins and dyneins ____________________. (a) have tails that bind to the filaments. (b) move along both microtubules and actin filaments. (c) often move in opposite directions to each other. (d) derive their energy from GTP hydrolysis.

(c) often move in opposite directions to each other

Which of the following structures shorten during muscle contraction? (a) myosin filaments (b) flagella (c) sarcomeres (d) actin filaments

(c) sarcomeres

The microtubules in a cell form a structural framework that can have all the following functions except which one? (a) holding internal organelles such as the Golgi apparatus in particular positions in the cell (b) creating long, thin cytoplasmic extensions that protrude from one side of the cell (c) strengthening the plasma membrane (d) moving materials from one place to another inside a cell

(c) strengthening the plasma membrane

. Which of the following signaling components is a second messenger? (a). PKA (b). acetylcholine (c). Calcium (d) NFAT

(c). Calcium

How is skeletal muscle contraction regulated by calcium? (a). Calcium binds to actin and causes the thin filaments to slide. (b). Calcium binds to tropomyosin and induces a conformational change. (c). Calcium binds to troponin and exposes myosin binding sites on thin filaments.(d). Calcium binds to calmodulin and activates the ATPase activity of myosin. (e). Calcium binds to myosin and activates its ATPase activity.

(c). Calcium binds to troponin and exposes myosin binding sites on thin filaments.

SH2 domain-containing proteins bind to which of the following proteins? (a). phospholipase (b). MAP kinase (c). PDGFR (d). Ras (e). Myc

(c). PDGFR

Which if the following proteins contain switch helix? (a). phospholipase (b). MAP kinase (c). Ras (d). Albumin (e). tyrosine-kinase receptors

(c). Ras

Which of the following statements about the cytoskeleton is true? (a) All eukaryotic cells have actin, microtubules, and intermediate filaments in their cytoplasm. (b) The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell. (c) The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another. (d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.

(d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.

Which 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 of the statements below about intermediate filaments is false? (a) They can stay intact in cells treated with concentrated salt solutions. (b) They can be found in the cytoplasm and the nucleus. (c) They can be anchored to the plasma membrane at a cell-cell junction. (d) Each filament is about 10 μm in diameter.

(d) Each filament is about 10 μm in diameter.

Lipids can also partake in relaying signals in the cell, as seen when _____ cleaves the sugar-phosphate head off a lipid molecule to generate the two small messenger molecules. (a)PI3K (b) PTEN (c) MAPK (d) PLC

(d) PLC

Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties is not true of these types of intermediate filaments? (a) They strengthen cells against mechanical stress. (b) Dimers associate by noncovalent bonding to form a tetramer. (c) They are found in the cytoplasm. (d) Phosphorylation causes disassembly during every mitotic cycle

(d) Phosphorylation causes disassembly during every mitotic cycle

Cell movement involves the coordination of many events in the cell. Which of the following phenomena is not required for cell motility? (a) Myosin-mediated contraction at the rear of the moving cell. (b) Integrin association with the extracellular environment. (c) Nucleation of new actin filaments. (d) Release of Ca2+ from the sarcoplasmic reticulum

(d) Release of Ca2+ from the sarcoplasmic reticulum

Which 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

(d) 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 about actin is false? (a) ATP hydrolysis decreases actin filament stability. (b) Actin at the cell cortex helps govern the shape of the plasma membrane. (c) Actin filaments are nucleated at the side of existing actin filaments in lamellipodia. (d) The dynamic instability of actin filaments is important for cell movement

(d) The dynamic instability of actin filaments is important for cell movement

The hydrolysis of GTP to GDP carried out by tubulin molecules ________________. (a) provides the energy needed for tubulin to polymerize. (b) occurs because the pool of free GDP has run out. (c) tips the balance in favor of microtubule assembly. (d) allows the behavior of microtubules called dynamic instability.

(d) allows the behavior of microtubules called dynamic instability.

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. (a) endocrine (b) paracrine (c) neuronal (d) contact-dependent

(d) contact-dependent

For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______. (a) stabilizing the filaments once they are formed. (b) increasing the rate at which subunits are added to the filaments. (c) promoting nucleation of filaments. (d) decreasing the binding strength between subunits on filaments.

(d) decreasing the binding strength between subunits on filaments.

The PDGFR is a typical receptor tyrosine kinase. Therefore, it does ________. (a). require G proteins (b). bind to proteins with PH domains (c). have seven transmembrane domains (d) form a dimer

(d) form a dimer

All members of the steroid hormone receptor family __________________. (a) are cell-surface receptors. (b) do not undergo conformational changes. (c) are found only in the cytoplasm. (d) interact with signal molecules that diffuse through the plasma membrane.

(d) interact with signal molecules that diffuse through the plasma membrane.

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) myosin

All GPCRs have a similar structure with ______ transmembrane regions. (a) single (b) two (c) three (d) seven

(d) seven

The length of time a G protein will signal is determined by _______. (a) the activity of phosphatases that turn off G proteins by dephosphorylating Gα. (b) the activity of phosphatases that turn GTP into GDP. (c) the degradation of the G protein after Gαseparates from Gβγ (d) the GTPase activity of Gα

(d) the GTPase activity of Gα

Which of the following statements about the structure of microtubules is false? (a) Microtubules are built from protofilaments that come together to make a hollow structure. (b) The two ends of a protofilament are chemically distinct, with α-tubulin exposed at one end and β-tubulin exposed at the other end. (c) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity. (d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

(d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into

Both Phospholipase C and ________ utilize PI-4,5-P2 as their substrate. (a). PKB (b). PKC (c). MAPK (d). PI3K (e). Ras

(d). PI3K

Circle the phrase in each pair that is likely to occur more rapidly in response to an extracellular signal. A. changes in cell secretion / increased cell division B. changes in protein phosphorylation / changes in proteins being synthesized C. changes in mRNA levels / changes in membrane potential

A. changes in cell secretion B. changes in protein phosphorylation C. changes in membrane potential

Match the target of the G protein with the appropriate signaling outcome. adenylyl cyclase ________ ion channels _________ phospholipase C _________ A. cleavage of inositol phospholipids _________ B. increase in cAMP levels C. changes in membrane potential

B C A

Place the following in order of size, from the smallest to the largest. A. protofilament B. microtubule C. α-tubulin D. tubulin dimer E. mitotic spindle

C, D, A, B, E

Some intracellular signaling pathways involve chains of protein kinases that phosphorylate each other, as seen in the ______ signalling module. (a)PI3K (b) PTEN (c) MAPK (d) PLC

c) MAPK

Indicate which of the three major classes of cytoskeletal elements each statement below refers to. A. monomer that binds ATP B. includes keratin and neurofilaments C. important for formation of the contractile ring during cytokinesis D. supports and strengthens the nuclear envelope E. their stability involves a GTP cap F. used in the eukaryotic flagellum G. a component of the mitotic spindle H. can be connected through desmosomes I. directly involved in muscle contraction J. abundant in filopodia

A. actin B. intermediate filaments C. actin D. intermediate filaments E. microtubules F. microtubules G. microtubules H. intermediate filaments I. actin J. actin

Indicate whether each of the following statements refers to a ciliary microtubule, a microtubule of the mitotic spindle, both types of microtubule, or neither type of microtubule. A. The basal body is the organizing center. B. The monomer is sequestered by profilin. C. It is arranged in a "9 + 2" array. D. It is nucleated at the centrosome. E. It uses dynein motors. F. It is involved in sperm motility. G. It is involved in moving fluid over the surface of cells.

A. ciliary microtubules B. neither C. ciliary microtubules D. microtubules of the mitotic spindle E. both F. neither (this involves flagellar microtubules) G. ciliary microtubules

Match the class of cell-surface receptor with the best description of its function. Not all descriptors will be used. G-protein-coupled receptors ______ ion-channel-coupled receptors ______ 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 cells

D A E

Cells signal to one another in various ways. Some use extracellular signal molecules that are dissolved gases, such as __________________, which can diffuse easily into cells. Others use cytokines, which bind to cytokine receptors. Cytokine receptors have no intrinsic enzyme activity but are associated with cytoplasmic tyrosine kinases called __________________s, which become activated on the binding of cytokine to its receptor and go on to phosphorylate and activate cytoplasmic transcriptional regulators called __________________s. Some intracellular signaling pathways involve chains of protein kinases that phosphorylate each other, as seen in the __________________ signaling module. Lipids can also relay signals in the cell, as we observe when phospholipase C cleaves the sugar-phosphate head off a lipid molecule to generate the two small messenger molecules __________________ (which remains embedded in the plasma membrane) and __________________ (which diffuses into the cytosol cyclic GMP MAP kinase STAT diacylglycerol NO TGFβ IP3 Ras JAK SMAD

NO JAK STAT MAP Kinase diacyhlycerol IP3

G-protein-coupled receptors (GPCRs) all have a similar structure with __________________ transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of __________________ subunits, becomes activated. __________________ of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to __________________, which is exchanged for __________________ on stimulation. The intrinsic __________________ activity of the α subunit is important for inactivating the G protein. __________________ inhibits this activity of the α subunit, thereby keeping the subunit in an active state. adenylyl cyclase cholera toxin GTPase AMP diacylglycerol phosphodiesterase ATP five seven ATPase four three Ca2+ GDP twelve cAMP GTP two

Seven Three Two GDP GTP GTPase Cholera

Directionl movement in response to a graded chemical stimulus is known as__ a. chemotaxis b. chemopropulsion c. chemotherapy d. chemotrophy e. chemosensing

a. chemotaxis

Which answer shows teh correct order of the flow of information during cell signaling? a. receptor-ligand binding, signal transduction, change in gene expression b. change in gene expression,signal transduction, receptor-ligand binding c. change in gene expression,signal transduction, receptor-ligand binding d. signal transduction, change in gene expression, receptor-ligand binding,

a. receptor-ligand binding, signal transduction, change in gene expression

Calmodulin is essential for Troponin dissociation from F-Actin in skeletal muscle. (a) True (b) False

b) False

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.

Cyclic AMP is ________. (a). an allosteric regulator of Gα (b) an allosteric regulator of PKA (c). an allosteric regulator of phosphodiesterase (d). an allosteric regulator of protein kinase B (e). an allosteric regulator of phospholipase C

b) an allosteric regulator of PKA

Which is true ? a. MAP kinase is important for phosphorylating MAP Kinase b. PI 3 - kinase phosphorylates a lipis in the plasma mebrane c. Ras becomes activated when a RTK phosporylates its bound GDP to create GTP d. STAT proteins phosphorylates JAK proteins , which then enters the nucleus and activates gene transcription

b. PI 3 - kinase phosphorylates a lipis in the plasma mebrane

Cyclic AMP is a. an allosteric regulator of Ga b. an allosteric regulator of PKA c. an allosteric regulator of phosphodiesterase d.an allosteric regulator of protein kinase B e. an allosteric regulator of phosphodiesterase C

b. an allosteric regulator of PKA

Cells can signal to each other in various ways. A signal that must be relayed to the entire body is most efficiently sent by __________________ cells, which produce hormones that are carried throughout the body through the bloodstream. On the other hand, __________________ methods of cell signaling do not require the release of a secreted molecule and are used for very localized signaling events. During __________________ signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells. Finally, __________________ signaling involves the conversion of electrical impulses into a chemical signal. Cells receive signals through a __________________, which can be an integral membrane protein or can reside inside the cell. amplification G protein phosphorylation contact-dependent K+ channel receptor endocrine neuronal target epithelial paracrine

endocrine contact-dependent paracrine neuronal receptor

Intermediate filaments are elongated fibrous proteins with an N-terminal globular _________________ region and a C-terminal globular _________________ region; these regions flank the elongated rod domain. The α-helical region of the rod interacts with the α-helical region of another monomer in a _____________________ configuration to form a dimer. ______________ dimers will line up to form a staggered tetramer. ______________ strands of tetramers come together and twist together to form the _________________ nm filament. The ___________________ domains are exposed on the surface of the intermediate filament, allowing for interaction with cytoplasmic components. antiparallel four tail β barrel globular ten coiled-coil head trimeric covalent rod twenty-five eight seven two

head tail coiled-coil two eight ten globular

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 in the cell. The cAMP molecules then activate a cAMP-dependent kinase (PKA) that, in turn, activates enzymes that result in the breakdown of muscle glycogen, thus lowering glycogen levels. You obtain muscle cells that are defective in various components of the signaling pathway. Referring to Figure Q16-36, indicate how glycogen levels would be affected in the presence of adrenaline in the following cells. Would they be higher or lower than in normal cells treated with adrenaline? A. cells that lack adenylyl cyclase B. cells that lack the GPCR C. cells that lack cAMP phosphodiesterase D. cells that have an α subunit that cannot hydrolyze GTP but can interact properly with the β and γ subunits

higher higer lower lower

Intermediate filaments are found mainly in cells that are subject to mechanical stress. Gene mutations that disrupt intermediate filaments cause some rare human genetic diseases. For example, the skin of people with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their __________________ genes, which code for the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called __________________s. The main filaments found in muscle cells belong to the __________________ family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervous system, __________________s help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for __________________, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex, muscular dystrophy, and neurodegeneration. Humans with progeria, a disease that causes premature aging, carry mutations in a nuclear ____________. desmosome lamin synapse keratin neurofilament vimentin kinase plectin

keratin desmosome vimentin neurofilament plectin lamin

Match the type of intermediate filament with its appropriate location. lamins _________ A. nerve cells neurofilaments _________ B. epithelia vimentins _________ C. nucleus keratins _________ D. connective tissue

lamins ____C____ neurofilaments ____A____ vimentins ____D____ keratins ____B____

An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface __________________ that control intracellular signaling proteins. These intracellular signaling proteins ultimately change the activity of __________________ proteins that bring about cell responses. Intracellular signaling proteins can __________________ the signal received to evoke a strong response from just a few extracellular signal molecules. A cell that receives more than one extracellular signal at the same time can __________________ this information using intracellular signaling proteins. __________________ proteins can act as molecular switches, letting a cell know that a signal has been received. Enzymes that phosphorylate proteins, termed ___________, can also serve as molecular switches; the actions of these enzymes are countered by the activity of __________________. acetylase decouple GTP-binding AMP-binding decrease neurotransmitter amplify effector protein kinases autocrine esterases protein phosphatases cleavage integrate receptors convolute GMP-binding sterols

receptors effector amplify integrate GTP-binding protein kinases protein phosphatases

You are interested in cell-size regulation and discover that signaling through an enzyme-coupled receptor is important for the growth (enlargement) of mouse liver cells. Activation of the receptor activates adenylyl cyclase, which ultimately leads to the activation of PKA, which then phosphorylates a transcription factor called TFS on threonine 42. This phosphorylation is necessary for the binding of TFS to its specific sites on DNA, where it then activates the transcription of Sze2, a gene that encodes a protein important for liver cell growth. You find that liver cells lacking the receptor are 15% smaller than normal cells, whereas cells that express a constitutively activated version of PKA are 15% larger than normal liver cells. Given these results, predict whether you would expect the cell's size to be bigger or smaller than normal cells if cells were treated in the following fashion. A. You change threonine 42 on TFS to an alanine residue. B. You create a version of the receptor that is constitutively active. C. You add a drug that inhibits adenylyl cyclase. D. You add a drug that increases the activity of cyclic AMP phosphodiesterase. E. You mutate the cAMP-binding sites in the regulatory subunits of PKA, so that the complex binds cAMP more tightly.

smaller bigger smaller smaller bigger

Microtubules are formed from the tubulin heterodimer, which is composed of the nucleotide-binding __________________ protein and the __________________ protein. Tubulin dimers are stacked together into protofilaments; __________________ parallel protofilaments form the tubelike structure of a microtubule. __________________ rings are important for microtubule nucleation and are found in the __________________ , which is usually found near the cell's nucleus in cells that are not undergoing mitosis. A microtubule that is quickly growing will have a __________________ cap that helps prevent the loss of subunits from its growing end. Stable microtubules are used in cilia and flagella; these microtubules are nucleated from a __________________ and involve a "__________________ plus two" array of microtubules. The motor protein __________________ generates the bending motion in cilia; the lack of this protein can cause Kartagener's syndrome in humans. α-tubulin dynein nine ATP four thirteen basal body γ-tubulin twenty-one β-tubulin GTP UTP centrosome kinesin two vimentin δ-tubulin myosin

β-tubulin α-tubulin thirteen Tubulin centrosome basal body dynein Kartagener