Cell Bio Exam 4

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A growing microtubule has

(a) GTP bound to the β-tubulin subunits at the microtubule end.

what is the death receptor?

Fas receptor

16-19 __________________ 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 __________________

GTP-binding; protein kinases; protein phosphatatses

Which of the following statements about the cell cycle is false? • (a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eucaryotic cells. • (b) An unfavorable environment can cause cells to arrest in G1. • (c) A cell has more DNA during G2 than it did in G1. • (d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases.

(a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eucaryotic cells.

Acetylcholine binds to a G protein coupled receptor (GPCR) on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in the figure. Which of the following would enhance this effect of the acetylcholine?

(a) addition of a high concentration of a non-hydrolyzable analog of GTP that cannot be converted to GDP

You create cells with a version of Cdc6 that cannot be phosphorylated and thus cannot be degraded. Which of the following statements describes the likely consequence of this change in Cdc6?

(b) Cells will be unable to complete DNA synthesis.

Cells that are terminally differentiated ______________________.

(b) can no longer undergo cell division

The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation? • (a) a mutation that prevents dimerization of the receptor • (b) a mutation that destroys the kinase activity of the receptor • (c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor • (d) a mutation that prevents the binding of the normal extracellular signal to the receptor

(c) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor

The figure shows how normal signaling works with a Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line?

The concentration of mitotic cyclin (M cyclin) ________________.

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

Akt promotes the survival of many cells. It is activated by an intracellular signaling pathway that is triggered by a receptor tyrosine kinase (RTK) that activates PI 3-kinase. • • Which of the following statements is false? • (a) In the presence of a survival signal, Akt localizes to the plasma membrane by binding to PIP3. • (b) In the absence of survival signal, Bad inhibits the cell death inhibitor protein Bcl2. • (c) In the presence of survival signal, the cell death inhibitory protein Bcl2 is active. • (d) In the absence of survival signal, Bad is phosphorylated.

(d) In the absence of survival signal, Bad is phosphorylated.

Both multicellular plants and animals have _____________________.

(d) tissues composed of multiple different cell types

Name a connective tissue.

- Bone - Tendon - Dermis of the skin - Cartilage

these monomeric GTP binding proteins are aided by two sets of regulatory proteins which are --------and-----

1) guanine nucleotide exchange factors (GEFs) activate the switch proteins by promoting the exchange of GDP and GTP (switch on) GTPase activating proteins (GAPs) turn them off by promoting GTP hydrolysis (switch off)

two main types of GTP binding proteins participate in intracellular signalling pathways which are --------and-----

1) large, trimeric GTP binding proteins (also called G-proteins) which relay messages from GPCR 2) small monomeric GTPase to help relay their signals

what determines the response of a cell to a signal?

1) presence or absence of the receptor 2) presence or absence of intracellular signaling molecules and intracellular effector proteins -lead to change in gene expression, metabolism, movement, shape, status 3) combinations of signals give different responses

two main types of protein kinases operate in intracellular signalling pathways: the most common are -------

1) serine/threonine kinases (phosphorylate proteins on serines or threonine. 2) tyrosine kinases (phosphorylate proteins on tyrosine

a typical path of reactions would follow which sequence? 1)binding of a hormone to a receptor 2) synthesis of cyclic AMP 3)phosphorylation of the target enzyme 4) release of a G protein from the interior cell membrane 5) activation of a protein kinase

1,4,2,5,3

calmodulin has a dumbbell shape with two globular ends connected by a long helix. each end has ____ Ca2+ binding domains.

16-3 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

2 1 3 4

when a GCPR 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 a subunit is bound to ____ which is exchanged for ____ on stimulation. the intrinsic ____ activity of the a subunit is important for inactivating the G protein. ______ inhibits this activity of the a subunit thereby keeping the subunit in an active state

3 protein 30 + 2 GDP GTP GTPase cholera toxin

18-39 Name the stage of M phase in which the following events occur. Place the numbers 1-8 next to the letter headings to indicate the normal order of events. A. alignment of the chromosomes at the spindle equator B. attachment of spindle microtubules to chromosomes C. breakdown of nuclear envelope D. pinching of cell in two E. separation of two centrosomes and initiation of mitotic spindle assembly F. re-formation of the nuclear envelope G. condensation of the chromosomes H. separation of sister chromatids

5, metaphase 4, prometaphase 3, prometaphase 8, cytokinesis 2, prophase 7, telophase 1, prophase 6, anaphase

GPCRS all have similar structures with --------transmembrane domains. when a GPCR binds an extracellular signal, an intracellular G proteins composed of ---------subunits, becomes activated. --------of the G-proteins are tethered to the plasma membrane by short lipid tails. when unstimulated, the alpha subunit is bound to --------which is exchanged for -------on stimulation. the intrinsic --------activity of the alpha subunit is important for inactivating the G-protein. --------inhibits this activity of the alpha subunit, thereby keeping the subunit in an active state.

7 3 2 GDP GTP GTPase cholera

A particular hormone is discovered to induce its effects by binding to surface proteins of receptor cells rather than passing through the membrane and activating intracellular receptors. This hormone is most likely which of the following types? a) peptide hormone b) steroid hormone c) hydrophilic hormone d) The answer cannot be determined with the given information.

A protein's functions are inhibited by a kinase. They activated by a phosphatase. Respectively, what are the actions of the kinase and phosphatase? a) phosphorylation, dephosphorylation b) dephosphorylation, phosphorylation c) Lower the system's overall kinetic energy, Increase the system's overall potential energy d) Increase the system's overall kinetic energy, Decrease the system's overall potential energy

All of the following are known to be part of a signal transduction cascade EXCEPT (A) phosphorylation of fibronectin (B) dissociation of the components of a heterotrimeric G-protein (C) enzymatic breakdown of phosphatidyl inositol bisphosphate (PIP2 ) (D) elevation of intracellular [Ca2+] (E) activation of cGMP phosphodiesterase

Consider a protein that contains an ER signal sequence at its N-terminus and a nuclear localization sequence in its middle. What would be the most likely fate of this protein? a) The protein would be translocated into the ER. b) The protein would be transported into the nucleus. c) The protein would remain in the cytoplasm. d) The protein would become part of the nuclear pore complex. e) The protein would be degraded.

Which of the following is TRUE? a) Akt is a kinase b) Akt is a phosphatase c) Viagra inhibits PI-3 kinase signaling d) The NO receptor translocates to the nucleus after binding NO, like other steroid recptors. e) PI-3 kinase inhibitors would increase erections

Which of the following is used to treat flunitrazepam overdoses? a) Romazicon, a benzodiazepine receptor antagonist b) BNZ2 agonists such as Clorazepate c) GABA d) Carisoprodol, a muscle relaxant e) All of the above would make the effects of flunitrazepam worse.

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.

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

do you expect garlic to improve erections? a) Yes b) No c) There is no reason to think it will have any effect at all

18-49 Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G1 phase. How many of each of the following structures will the cell have at mitotic prophase? A. sister chromatids B. centromeres C. kinetochores D. centrosomes E. centrioles

A-16 B-16 C-16 D02 E-4

Which of the following is true in reference to G protein signaling? • a. Hormone binding induces an interaction of the receptor with the G protein, stimulating the release of GDP and the exchange of GTP on the α subunit. • b. Once activated, the GTP-bound α subunit dissociates from β/γ and interacts with its target. • c. Activity of the α subunit is terminated by the hydrolysis of GTP to GDP. • d. All of the above

ALL OF THE ABOVE

cyclic AMP (cAMP) is formed from ____ by a crystallization reaction that removes two phosphate groups from ____ and joins the "free" end of the remaining phosphate group to the sugar part of the AMP molecule. The degradation reaction breaks this new bond, forming AMP. _____ continuously converts cAMP to AMP.

ATP ATP cyclic AMP phosphodieterase

cyclic AMP is formed from ---------by the cyclization reaction removes two phosphate groups from -------and joins free end of the remaining phosphate group to the sugar part of the AMP molecule. the degradation reaction breaks this new bond, forming AMP.----------continuously converts cAMP to AMP

ATP ATP cyclic amp phosphodiester

In cells, dynamic instability typically occurs

At (+) ends only.

Viagra promotes erections. How? a) Viagra is a guanylyl cyclase inhibitor b) Viagra inhibits cGMP phosphodiesterase c) Viagra inhibits nitric oxide synthase d) Viagra inhibits Akt signaling e) Viagra inhibits heterotrimeric G proteins

Which of the following is a second messenger that stimulates release of calcium ions into the cytoplasm? a) Prostaglandins b) Inositol triphosphate c) Cyclic AMP d) Calmodulin

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.

16-43 Match the target of the G protein with the appropriate signaling outcome. adenyly cysclase.... ion channels... phospholipase C... a. cleavage of inositol phospholipids b. increase in cAMP levels c. changes in membrane potential

B C A

18-24 Irradiated mammalian cells usually stop dividing and arrest at a G1 checkpoint. Place the following events in the order in which they occur. A. production of p21 B. DNA damage C. inhibition of cyclin-Cdk complexes D. accumulation and activation of p53

B D A C DNA damage accumulation and activation of p53 production of p21 inhibition of cyclin-Cdk complexes

18-72 Of the following mutations, which are likely to cause cell-cycle arrest? If you predict a cell-cycle arrest, indicate whether the cell will arrest in early G1, late G1, or G2. Explain your answers. A. a mutation in a gene encoding a cell-surface mitogen receptor that makes the receptor active even in the absence of the mitogen B. a mutation that destroyed the kinase activity of S-Cdk C. a mutation that allowed G1-Cdk to be active independently of its phosphorylation status D. a mutation that removed the phosphorylation sites on the Rb protein E. a mutation that inhibited the activity of Rb

B and D will cause cell-cycle arrest

A receptor ligand that does not elicit a biological response but binds to a receptor and blocks other molecules from eliciting responses is called a) ligand antagonist b) ligand agonist c) receptor antagonist d) receptor agonist

All of the following statements about monomeric G proteins are true EXCEPT: (A) They are regulated by GTP-GDP exchange proteins. (B) They are regulated by GTPase activating proteins. (C) They regulate enzymes that synthesize cGMP . (D) They regulate vesicle formation. (E) They regulate vesicle fusion.

Gamma-aminobutyric acid-A (GABA-A) receptors are GABA-gated chloride channels. They are found in the plasma membrane of certain types of neurons. Which of the following is TRUE? a) GABA-A receptors are synthesized by ribosomes in the nucleus. b) GABA is a steroid hormone. c) When GABA-A receptors are being synthesized, their ligand-binding site is inside the lumen of the ER. d) Benzodiazepines reduce chloride flow through the plasma membrane. e) GABA-A receptors have seven transmembrane segments.

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.

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

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.

Which of the following is not a protein? a) adenylate cyclase b) PKA c) cAMP d) IP3 receptor e) PLC

Which of the following statements is true? a) Calcium and diacylglycerol in combination activate adenylate cyclase. b) Many enzyme-coupled receptors (such as receptor tyrosine kinases) have intracellular protein domains that interact with heterotrimeric G-proteins. c) In all eukaryotic cells, transport vesicles continually bud from the trans golgi network and fuse with the plasma membrane, a process called 'constitutive exocytosis'. d) Ribosomes in the cytosol are directed to the ER because the protein they are making has an ER signal sequence, which is recognized by a signal recognition particle inside the lumen of the ER. e) All of the statements above are true.

Which of the following statements is true? a) Large hydrophilic extracellular signal molecules such as steroid hormones and nitric oxide cannot diffuse directly across the plasma membrane. Thus, they bind to intracellular receptors, which usually act as transcription regulators or enzymes when activated. b) There are three main classes of cell-surface receptors: 1) adenylate cyclase, 2) phospholipase C, and 3) nitic oxide synthase. c) GPCRs activate a class of trimeric GTP-binding proteins called G proteins; these act as molecular switches, transmitting the signal onward for a short period and then switching themselves off by hydrolyzing GTP to GDP. d) IP3 opens calcium channels in the membrane of the endoplasmic reticulum, allowing calcium ions to flow from the cytosol into the ER. e) Protein kinase A is responsible for the synthesis of cAMP.

Your friend is studying mouse fur color and has isolated the GPCR responsible for determining its color, as well as the extracellular signal that activates the receptor. She finds that, on addition of the signal to pigment cells (cells that produce the pigment determining fur color), cAMP levels rise in the cell. She starts a biotech company, and the company isolates more components of the signaling pathway responsible for fur color. Using transgenic mouse technology, the company genetically engineers mice that are defective in various proteins involved in determining fur color. The company obtains the following results. Normal mice have beige (very light brown) fur color. Mice lacking the extracellular signal have white fur. Mice lacking the GPCR have white fur. Mice lacking cAMP phosphodiesterase have dark brown fur. Your friend has also made mice that are defective in the α subunit of the G protein in this signaling pathway. The defective α subunit works normally except that, once it binds GTP, it cannot hydrolyze GTP to GDP. What color do you predict that the fur of these mice will be? a) very light brown b) white c) dark brown d) black

"Androgel" is testosterone dissolved in a gel. It is rubbed onto the skin as 'testosterone replacement therapy' to treat low testosterone, most often in males. Which of the following is TRUE? a) Testosterone cannot penetrate membranes, and therefore is unlikely to penetrate the skin. b) Testosterone binds to G-protein coupled receptors. c) Androgel is a testosterone receptor antagonist. d) Testosterone receptor antagonists would block the effect of Androgel. e) Androgel is a receptor in the cytoplasm, which travels to the nucleus when testosterone binds.

Naloxone is a drug given to individuals who present in the emergency room suspected of opiate overdose (such as heroin). Naloxone acts on opiate receptors to block the binding of the opiates in the body, thus negating their toxic effects. The drug acts quite quickly such that patients will suddenly wake up from unconsciousness upon administration. Naloxone has a half-life of around 30 minutes (as compared with 4 hours for many opiates). As such, the patient may revert into the unconscious state when the naloxone effects have worn off and the opiates continue to have their effects. Which of the following types of inhibition is POSSIBLE of the naloxone-opiate receptor system? I. Noncompetitive inhibitor II. Competitive inhibitor III. Nonreversible Inhibitor a) I only b) II only c) II and III only d) I, II, and III

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

Which of the following canonical signaling cascades is NOT correctly described? a) Phospholipase C (PLC) cleaves PIP2 into IP3 and DAG; DAG then activates protein kinase C. b) RAS activates RAF, which phosphorylates a MAP kinase kinase, which phosphorylates a MAP kinase, which phosphorylates a transcription factor. c) IP3 triggers opening of IP3 receptors in the endoplasmic reticulum, allowing calcium to move from the ER to the cytoplasm. d) A GTPase-activating protein (GAP) turns on RAS by triggering release of GDP and binding of GTP. e) Mechanical pressure on the extracellular portion of a mechanoreceptor causes opening of an ion channel portion of the receptor, allowing calcium into the cytoplasm.

Which of the following is the most accurate description of intercellular (cell to cell) chemical signaling? a) A signal molecule binds to a receptor in the plasma membrane, triggering activation of G-proteins that activate other proteins by phosphorylation. These phosphorylated proteins cause a cellular response b) A signal molecule binds to a receptor, which is by definition any sort of protein that binds the signal molecule. After this receptor binds the signaling molecule (also called a 'ligand'), the receptor converts to an adenylate cyclase and generates CaM kinase, which phsophorylates other proteins, eventually leading to a cellular response c) A signal molecule, typically named Bob, wanders down the street until it bumps into a lamppost and falls over. Somewhere, a dog howls. d) A signal molecule binds to a receptor, which can be inside the cell or embedded in the plasma membrane, causing activation of this receptor. Receptor activation then triggers a 'signaling cascade', in which a series of enzymes (such as CaM kinase, protein kinase, and adenylate cyclase) catalyze the formation of other signaling molecules that eventually activate a cellular response. e) Signaling molecules can be released from nearby cells ('endocrine signaling'), transported from cells far away (paracrine signaling), or the target cell itself ('autocrine signaling'). In each case, the signaling molecule binds to receptors on or in the target cell to cause either a change in intracellular ion concentration (i.e. an increase in intracellular calcium) or activation of intracellular G-proteins or enzymes like kinases. G-proteins and kinases in turn activate other proteins and/or generate 'second messengers', which eventually leads to a cellular response

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.

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.

about one third of all drugs used today work through -----

GPCRs

Assuming memory formation requires activation of the PKA pathway leading to CREB phosphorylation, which of the following pills might make you smart? a) An adenylyl cyclase antagonist b) A MAP Kinase antagonist c) A Guanylyl cyclase agonist d) An inhibitor of Ras e) A phosphodiesterase inhibitor

The KDEL sequence, found on luminal proteins of the ER, is responsible for (A) translocation of proteins into the ER lumen (B) insertion of proteins into the membrane of the ER (C) quality control in the ER (D) recognition by signal peptidase of the signal sequence (E) retrieval of ER luminal proteins from the Golgi

one important system invovles hormones that stimulate a membrane bound ------which the stimulates adenylate to produce cAMP (in this case cAMP is a second messenger

G-protein

GPCRS stands for

G-protein coupled receptors

18-1 Growth occurs in __________________, __________________, and __________________ phases of the cell cycle. A cell does not enter mitosis until it has completed __________________ synthesis.

G1 S G2 DNA

18-31 Cells can pause in G1 when DNA is damaged, and can pause in S when there are replication errors. Indicate whether the mechanism below applies to a G1 arrest, an S-phase arrest, both types of arrest, or neither. A. p53 activates the transcription of a Cdk inhibitor. B. Cyclins are phosphorylated and destroyed. C. Cdk is unable to phosphorylate its substrates. D. The Cdc25 phosphatase is inhibited.

G1 arrest neither both S-phase arrest

16-27 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.

GTPase; cholera toxin

When the neurotransmitter acetylcholine is applied to skeletal muscle cells, it binds the acetylcholine receptor and causes the muscle cells to contract. Succinylcholine, which is a chemical analog of acetylcholine, binds to the acetylcholine receptor on skeletal muscle cells but causes the muscle cells to relax; it is therefore often used by surgeons as a muscle relaxant. Propose a model for why succinylcholine causes muscle relaxation. What might be the mechanism to explain the different activities of acetylcholine and succinylcholine on the acetylcholine receptor?

Given that Succinylcholine is a chemical analog of acetylcholine (Ach), they likely have very similar structures. This is supported by the fact that both molecules bind to the same (Ach) receptor. The most likely explanation is that Ach binding to its receptor produces a cascade (or other response) that results in muscle cell contraction while Succinylcholine binding to the same receptor interferes with Ach binding; further, Succinylcholine binding to the receptor does not induce a receptor shape-change that results in intracellular signaling. This blocking of Ach-induced contraction results in muscle cell relaxation (i.e., the absence of contraction—no signal to contract). Simply put, Succinylcholine is a competitive inhibitor of Ach binding.

Which of the following is not a commonly observed consequence of the binding of a signaling molecule to its cell surface receptor? • a. Receptor dimerization • b. Receptor phosphorylation • c. Conformational changes in the receptor • d. Increased synthesis of the receptor

Increased synthesis of the receptor

What type of activity would a cytosolic receptor be expected to have if it typically elicits a very rapid cellular response after binding to its chemical signaling molecule?

It is likely that the cytosolic receptor has some sort of enzymatic activity (like the guanalyl cyclase activity described in class for NO) because a rapid response would be elicited when the receptor were bound by a signaling molecule that could pass through the membrane. Upon the signal molecule's binding to the cytosolic receptor, the receptor would change shape and alter its activity (either up or down) to alter cellular behavior rapidly.

18-32 The cell cycle consists of an alternation between __________________, which appears as a period of dramatic activity under the microscope, and a preparative period called __________________, which consists of three phases called __________________, __________________, and __________________.

M phase interphase G1 phase S phase G2 phase

16-53 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)

MAP kinase; diacylglycerol; IP3

16-53 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

NO; JAK STAT;

activated --------can also phosphorylate aNd thereby regulate other proteins and enzymes in the cystosol

PKA

cyclic AMP exerts its effects in animal cells mainly by activating the enzyme ____ which catalyzes the transfer of the terminal phosphate group from ATP to specific serines or threonines of selected proteins

PKA

the increase in cyclic AMP activates ________, which phosphorylates and activates an enzyme called phosphorylase kinase

PKA

the enzyme activated by diacylglycerol is called ------becasue it is Ca+ dependent

PKC

Diacylglycerol activates which of the following enzymes? - A. Protein kinase A - B. Protein kinase C - C. MAP kinase - D. Tyrosine kinase - E. Phosphorylase b kinase

Protein kinase C

18-1 The four phases of the cell cycle, in order, are G1, __________________, __________________, and __________________. A

S G2 M

18-1 A cell contains the most DNA after __________________ phase of the cell cycle. A cell is smallest in size after __________________ phase of the cell cycle

S M

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only?

The cells produced would get smaller and smaller.

The lab you work in has discovered a previously unidentified extracellular signal molecule called X, a 75,000-dalton protein. You add purified protein X to different types of cells to determine its effect(s). When you add protein X 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. How might these observations be explained?

The differences in response (or lack thereof) are easily explained by the presence/absence of a receptor for protein X, by the TYPE of protein X (different receptors yield different responses), and by the intracellular cascade(s) that occur after receptor binding. (i.e., even with the same receptor, different intracellular cascades can produce different cellular responses).

G proteins and monomeric GTPases are active when GTP is bound and inactive when GDP is bound. T/F?

True

16-32 Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in Figure Q16-32. Which of the following would enhance this effect of the acetylcholine? Figure Q16-32 (a) addition of a high concentration of a nonhydrolyzable analog of GTP (b) addition of a drug that prevents the α subunit from exchanging GDP for GTP (c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine (d) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein

a (addition of a high concentration of nonhydrolyzable analog of GTP)

18-32 During M phase, the nucleus divides in a process called __________________, and the cytoplasm splits in two in a process called __________________.

mitosis cytokinesis

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 before it encounters a responsive cell and 4 the type of signaling in which the signal molecule has the ability to travel the longest distance. ______ paracrine signaling ______ juxtacrine signaling ______ synaptic signaling ______ endocrine signaling

__3___ paracrine signaling __1___ juxtacrine signaling __2___ synaptic signaling __4___ endocrine signaling

18-26 Cells in the G0 state ________________. (a) do not divide. (b) cannot re-enter the cell cycle. (c) have entered this arrest state from either G1 or G2. (d) have duplicated their DNA.

16-40 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 cycle AMP phosphodiesterase to be hyperactive)

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

18-57 Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells? (a) assembly of the contractile ring (b) decondensation of chromosomes (c) reassembly of the nuclear lamina (d) transcription of nuclear genes

a (assembly of the contractile ring happens before reformation of nuclear envelope)

18-65 Programmed cell death occurs ________________. (a) by means of an intracellular suicide program. (b) rarely and selectively only during animal development. (c) only in unhealthy or abnormal cells. (d) only during embryonic development.

a (by means of an intracellular suicide program)

18-40 The principal microtubule-organizing center in animal cells is the ____________. (a) centrosome. (b) centromere. (c) kinetochore. (d) cell cortex.

a (centrosome-microtubule organizing center)

16-49 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)

16-22 Which of the following statements is true? (a) Extracellular signal molecules that are hydrophilic must bind to a cellsurface 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 cellsurface receptor so as to signal a target cell to change its behavior)

18-33 Which of the following does not occur during M phase in animal cells? (a) growth of the cell (b) condensation of chromosomes (c) breakdown of nuclear envelope (d) attachment of chromosomes to microtubules

a (growth of the cell)

18-50 Which of the following statements about kinetochores is true? (a) Kinetochores assemble onto chromosomes during late prophase. (b) Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome. (c) Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules. (d) Kinetochores assemble on chromosomes that lack centromeres.

a (kinetochores assemble onto chromosomes during late prophase)

18-22 Mitogens are _____. (a) extracellular signals that stimulate cell division. (b) transcription factors important for cyclin production. (c) kinases that cause cells to grow in size. (d) produced by mitotic cells to keep nearby neighboring cells from dividing. a (mitogens are extracellular signals that stimulate cell division)

a (mitogens are extracellular signals that stimulate cell division)

18-8 Which of the following statements about the cell cycle is false? (a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells. (b) An unfavorable environment can cause cells to arrest in G1. (c) A cell has more DNA during G2 than it did in G1. (d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases.

a (once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells)

16-23 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)

18-61 Cytokinesis in animal cells ________________. (a) requires ATP. (b) leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane. (c) is often followed by phosphorylation of integrins in the plasma membrane. (d) is assisted by motor proteins that pull on microtubules attached to the cell cortex.

a (requires ATP)

16-62 When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is true? (a) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras. (b) The cells you create will run out of the GTP necessary to activate Ras. (c) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras. (d) The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.

a (the cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras)

16-38 Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. Figure Q16-38 shows how G proteins can indirectly activate PKC. You have discovered the enzyme activated by PKC that mediates the lipid modification. You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells lacking Rafty do not have these modifications, even when PKC is active. Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty? Figure Q16-38 (a) the expression of a constitutively active phospholipase C (b) a mutation in the GPCR that binds the signal more tightly (c) a Ca2+ channel in the endoplasmic reticulum with an increased affinity for IP3 (d) a mutation in the gene that encodes Rafty such that the enzyme can no longer be phosphorylated by PKC

a (the expression of a constitutively active phospholipase C)

18-52 A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes? (a) the jiggling movement of chromosomes at the metaphase plate (b) the way in which chromosomes behave when the attachment between sister chromatids is severed (c) the way in which chromosomes behave when the attachment to one kinetochore is severed (d) the shape of chromosomes as they move toward the spindle poles at anaphase

a (the jiggling movement of chromosomes at the metaphase plate)

16-27 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.

seven; three

16-60 The ethylene response in plants involves a dimeric transmembrane receptor. When the receptor is not bound to ethylene, the receptor binds to and activates a protein kinase, which activates an intracellular signaling pathway that leads to the degradation of a transcriptional regulator important for transcribing the ethyleneresponsive genes (see Figure Q16-60). You discover a phosphatase that is important for ethylene signaling, and you name it PtpE. Plants lacking PtpE never turn on ethylene-responsive genes, even in the presence of ethylene. You find that PtpE dephosphorylates serine 121 on the transcriptional regulator. Furthermore, plants lacking PtpE degrade the transcriptional regulator in the presence of ethylene. Figure Q16-60 Which of the following statements is inconsistent with your data? (a) When the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-responsive genes. (b) When the transcriptional regulator is not phosphorylated, it binds to DNA. (c) Activation of the protein kinase that binds to the ethylene receptor leads to inactivation of PtpE. (d) Binding of ethylene to its receptor leads to the activation of PtpE.

a (when the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-responsive genes)

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration to RGF would be most likely to prevent receptor dimerization?

a mutation that prevents RGFR from binding to RGF

a second messenger is

a substance that brings about a desired effect in a cell as a result of a hormone binding to its receptor on the cell surface

a second messenger is ------

a substance that brings about a desired effect in a cell as a result of a hormone binding to its receptor on the cell surface

example of apoptosis in an animal

a tadpole becomes a frog by losing it's tail. the tail dies off (by apoptosis) to become a frog

reactions that invovle gene expression occur------

slowly

binding of the neurotransmitter ____ to its GPCR on the heart cells results in the activation of the G protein Gi. the _____ directly opens a ____ channel in the plasma membrane, increasing its permeability to ___ and thereby making the membrane harder to activate and ____ the heart rate. inactivation of the ____ by hydrolysis of its bound GTP returns the G protein to its inactive state, allowing the ___ channel to close

acetylcholine By complex K+ K+ lower K+

binding of the neurotransmitter ---------to its GPCR on the heart cells results in the activation of the G-protein , Gi. the -------directly opens a -------channel in the plasma membrane, increasing its permeability to -----------and thereby making the membrane harder to activate and ---------the heart rate. inactivation of the -------by hydrolysis of its bound GTP returns to its inactive state, allowing the -------channel to close

acetylcholine beta K+ K+ slow alpha subunit K+

an andrenaline activates a GPCR, which turns on a G-protein that activates --------to boost the production of cAMP. the increase in cAMP activates -------which phosphorylates and activates an enzyme called phosphorylase kinase. this kinase activates glycogen phosphorylase, the enzyme that breaks down glycogen. because these reactions do not involve changes in gene transcription or new protein synthesis, they occur ------

adenylyl cyclase PKA

an adrenaline activates a GPCR which turns on a G protein that activates ________ to boost the production of cyclic AMP

adenylyn cyclase

G- protein coupled receptors

all receptors for this class are polypeptides with seven transmembrane domains

ion channel coupled receptors

alter the membrane potential directly by changing the permeability of the plasma

Viagra targets a specific isoform of cGMP phosphodiesterase. Phosphodiesterases are made out of

amino acids

16-19 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.

amplify; integrate

Indicate whether the following molecules are found in plants, animals, or both. Collagen

animals

Indicate whether the following molecules are found in plants, animals, or both. Intermediate filaments

animals

BLANK helps regulate animal cell numbers

apoptosis

two ways that cells die

apoptosis necrosis

16-34 During the mating process, yeast cells respond to pheromones secreted by other yeast cells. These pheromones bind GPCRs on the surface of the responding cell and lead to the activation of G proteins inside the cell. When a wild-type yeast cell senses the pheromone, its physiology changes in preparation for mating: the cell stops growing until it finds a mating partner. If yeast cells do not undergo the appropriate response after sensing a pheromone, they are considered sterile. Yeast cells that are defective in one or more components of the G protein have characteristic phenotypes in the absence and presence of the pheromone, which are listed in Table 16-34. Table Q16-34 Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer. (a) α activates the mating response but is inhibited when bound to βγ (b) βγ activates the mating response but is inhibited when bound to α (c) the G protein is inactive; either free α or free βγ complex is capable of activating the mating response (d) the G protein is active; both free α and free βγ complex are required to inhibit the mating response

b (Beta v activates the mating response but is inhibited when bound to alpha)

16-54 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)

Elevation of intracellular inositol trisphosphate (IP3) results in a release of Ca2+ from what organelle?

smooth ER

16-18 Figure Q16-18 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine? Figure Q16-18 (a) a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO (b) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP (c) a muscle cell that has cyclic GMP phosphodiesterase constitutively active (d) a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO

b (a muscle cell that has a defect in guanlyl cyclase such that it constitutively converts GTP to cyclic GMP)

16-46 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 most likely prevents receptor dimerization)

16-52 Male cockroaches with mutations that strongly decrease the function of an RTK called RTKX are oblivious to the charms of their female comrades. This particular RTK binds to a small molecule secreted by sexually mature females. Most males carrying loss-of-function mutations in the gene for Ras protein are also unable to respond to females. You have just read a paper in which the authors describe how they have screened cockroaches that are mutant in RTKX for additional mutations that partly restore the ability of males to respond to females. These mutations decrease the function of a protein that the authors call Z. Which of the following types of protein could Z be? Explain your answer. (a) a protein that activates the Ras protein by causing Ras to exchange GDP for GTP (b) a protein that stimulates hydrolysis of GTP by the Ras protein (c) an adaptor protein that mediates the binding of the RTKX to the Ras protein (d) a transcriptional regulator required for the expression of the Ras gene

b (a protein that stimulates hydrolysis of GTP by the Ras protein)

16-50 You are interested in further understanding the signal transduction pathway that controls the production of Pig1, a protein important for regulating cell size. Activation of the TRK receptor leads to activation of the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE transcription factor. SZE only interacts with the nuclear transport receptor when it is phosphorylated. SZE is a gene activator for the Pig1 gene. This pathway is diagrammed in Figure Q16-50. Figure Q16-50 Normal cells grown under standard conditions (without ligand) are 14 µm in diameter while normal cells exposed to TRK ligand are 10.5 µm in diameter. Given this situation, which of the following conditions do you predict will more likely lead to smaller cells? (a) addition of TRK ligand and a drug that stimulates the GTPase activity of Ras (b) addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE (c) addition of TRK ligand and a drug that stimulates the degradation of Pig1 (d) addition of TRK ligand and a drug that inhibits Pig1 binding to DNA

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

18-34 Condensins ________________. (a) are degraded when cells enter M phase. (b) assemble into complexes on the DNA when phosphorylated by M-Cdk. (c) are involved in holding sister chromatids together. (d) bind to DNA before DNA replication begins.

b (assemble into complexes on the DNA when phosphorylate by M-Cdk)

18-30 You create cells with a version of Cdc6 that cannot be phosphorylated and thus cannot be degraded. Which of the following statements describes the likely consequence of this change in Cdc6? (a) Cells will enter S phase prematurely. (b) Cells will be unable to complete DNA synthesis. (c) The origin recognition complex (ORC) will be unable to bind to DNA. (d) Cdc6 will be produced inappropriately during M phase. b (cells will be unable to complete DNA synthesis)

b (cells will be unable to complete DNA synthesis)

16-57 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)

18-58 A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________________. (a) reassemble its nuclear envelope at telophase. (b) disassemble its nuclear lamina at prometaphase. (c) begin to assemble a mitotic spindle. (d) condense its chromosomes at prophase

b (disassemble its nuclear lamina at prometaphase)

18-64 Which organelle fragments during mitosis? (a) endoplasmic reticulum (b) Golgi apparatus (c) mitochondrion (d) chloroplast

b (golgi apparatus fragments)

16-15 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)

16-5 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)

18-3 A mutant yeast strain stops proliferating when shifted from 25°C to 37°C. When these cells are analyzed at the two different temperatures, using a machine that sorts cells according to the amount of DNA they contain, the graphs in Figure Q18-3 are obtained. Figure 18-3 Which of the following would not explain the results with the mutant? (a) inability to initiate DNA replication (b) inability to begin M phase (c) inability to activate proteins needed to enter S phase (d) inappropriate production of a signal that causes the cells to remain in G1

b (inability to begin M phase)

18-14 You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could not be responsible for the behavior of this strain of yeast? (a) inactivation of a protein kinase that acts on the mitotic Cdk kinase (b) inactivation of an enzyme that ubiquitylates M cyclin (c) inactivation of a phosphatase that acts on the mitotic Cdk kinase (d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M cyclin

b (inactivation of an enzyme that ubiquitylates M cyclin)

18-4 Which of the following events does not usually occur during interphase? (a) Cells grow in size. (b) The nuclear envelope breaks down. (c) DNA is replicated. (d) The centrosomes are duplicated.

b (nuclear envelope does not break down during interphase)

16-59

b (plants (fungi and animals))

16-1 Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F is known to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell line B does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques. You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in Table Q16-1. Table Q16-1 Which of the following cannot be concluded from your results above? (a) Binding of factor F to its receptor is required for proliferation of cell line A. (b) Receptor R binds to factor F to induce cell proliferation in cell line A. (c) Cell line A expresses a receptor for factor F. (d) Factor F is not required for proliferation in cell line B

b (receptor r binds to factor f to induce cell proliferation in cell line A)

18-11 Progression through the cell cycle requires a cyclin to bind to a Cdk because _________. (a) the cyclins are the molecules with the enzymatic activity in the complex. (b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity. (c) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle. (d) without cyclin binding, a cell-cycle checkpoint will be activated.

b (the binding of a cyclin to Cdk is required for Cdk enzymatic activity)

18-28 Which of the following statements is false? (a) DNA synthesis begins at origins of replication. (b) The loading of the origin recognition complexes (ORCs) is triggered by SCdk. (c) The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle. (d) DNA synthesis can only begin after prereplicative complexes assemble on the ORCs.

b (the loading of the origin recognition complexes (ORCs) is triggered by SCdk)

16-7 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)

Two cell lines, A and B, both survive but do not divide when they are cultured in vitro with a medium containing serum. Factor F is a protein that is known to stimulate cell division in cell line A. Cell line A produces a receptor protein (R) that cell line B does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques. You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in the table below. Cell Line Factor F Added Response A - No division A + Division B - No Division B + No Division B + Receptor R - Division B + Receptor R + Division Which of the following cannot be concluded from your results above? a.) Binding of factor F to its receptor is required for proliferation of cell line A. b.) Receptor R binds to factor F to induce cell proliferation in cell line A. c.) Cell line A expresses a receptor for factor F. d.) Factor F is not required for proliferation in cell line B.

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

the following reactions are all common parts of some hormone process: what is the right sequence binding of the hormone to the receptor synthesis of cyclic AMP phosphorylation of the target enzyme release of a Gprotein from the interior cell enzyme activation of protein kinase

bind, release, synthesise, activate, phosphorylate

Indicate whether the following molecules are found in plants, animals, or both. Microtubules

both

16-61 Figure Q16-61 shows that intracellular signaling pathways can be highly interconnected. Figure Q16-61 From the information in Figure Q16-61, which of the following statements is incorrect? (a) The GPCR and the RTK both activate phospholipase C. (b) Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators. (c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active. (d) Ras is activated only when the RTK is active and not when the GPCR is active

c (CaM-kinase is only activated when the GPCR is active and not when the RTK is active)

18-15 You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is least likely during this experiment? (a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase. (b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S phase. (c) G1 cyclins will be expressed during S phase. (d) S-Cdk targets will be phosphorylated during S phase

c (G1 cyclins will be expressed during S phase is not a likely outcome)

16-13 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,

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

18-23 The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______. (a) phosphorylating Cdk. (b) marking cyclins for destruction by proteolysis. (c) inhibiting cyclin transcription. (d) activating apoptosis.

c (Rb inhibiting cyclin transcription)

16-35 You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted in Figure Q16-35. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainy transcription? Figure Q16-35 (a) a mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA (b) a mutation in the nuclear import sequence of PKA from PPKKKRKV to PPAAAAAV (c) a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive (d) a mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein

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

16-45 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)

16-63 Figure Q16-63 shows how normal signaling works with a Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line? Figure Q16-63 (a) addition of a drug that prevents protein X from activating Ras (b) addition of a drug that increases the affinity of protein Y and Ras (c) addition of a drug that blocks protein Y from interacting with its target (d) addition of a drug that increases the activity of protein Y

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

18-35 At the end of DNA replication, the sister chromatids are held together by the ___________. (a) kinetochores. (b) securins. (c) cohesins. (d) histones.

c (at the end of DNA replication, the sister chromatids are held together by the cohesions)

difference between necrosis and apoptosis

necrosis is accidental apoptosis is controlled

18-66 Apoptosis differs from necrosis in that necrosis ________________. (a) requires the reception of an extracellular signal. (b) causes DNA to fragment. (c) causes cells to swell and burst, whereas apoptotic cells shrink and condense. (d) involves a caspase cascade

c (causes cells to swell and burst, whereas apoptotic cells shrink and condense)

16-17 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)

18-13 The concentration of mitotic cyclin (M cyclin) ________________. (a) rises markedly during M phase. (b) is activated by phosphorylation. (c) falls toward the end of M phase as a result of ubiquitylation and degradation. (d) is highest in G1 phase.

c (falls toward the end of M phase as a result of ubiquitylation and degradation)

16-26 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)

16-47 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)

18-54 Which of the following statements about the anaphase-promoting complex (APC) is false? (a) It promotes the degradation of proteins that regulate M phase. (b) It inhibits M-Cdk activity. (c) It is continuously active throughout the cell cycle. (d) M-Cdk stimulates its activity.

c (it is continuously active throughout the cell cycle)

18-29 How does S-Cdk help guarantee that replication occurs only once during each cell cycle? (a) It blocks the rise of Cdc6 concentrations early in G1. (b) It phosphorylates and inactivates DNA helicase. (c) It phosphorylates the Cdc6 protein, marking it for destruction. (d) It promotes the assembly of a prereplicative complex.

c (it phosphorylates the Cdc6 protein, marking it for destruction)

16-29 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 alpha subunit exchanges its bound GDP for GTP)

18-9 Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2? (a) The cell would be unable to enter M phase. (b) The cell would be unable to enter G2. (c) The cell would enter M phase under conditions when normal cells would not. (d) The cell would pass through M phase more slowly than normal cells

c (the cell would enter M phase under conditions when normal cells would not)

Nitric Oxide (NO) released from endothelial cells can result in the relaxation of underlying smooth muscle cells in vascular tissue. NO 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.

binding of an adrenaline molecule to its GPCR can lead to the activation of adenylyl cyclase and a rise in the concentration of ---------the increase in cAMP activates -------which the moves into the --------and phosphorylates specific transcription regulators.

cAMP PKA cystoso

if you activate BLANK, you can't do anything to stop is..

cascade

At the end of DNA replication, the sister chromatids are held together by the

cohesins

18-18 The components of MPF are evolutionarily __________________ from yeast to humans, so that the corresponding human genes are __________________ to function in yeast.

conserved able

caffeine acts as a stimulant by inhibiting what?

cyclic AMP phosphodiesterase in the nervous system blocking cyclic AMP degradation and keeping the concentration of cyclic AMP high

18-18 The regulatory component of MPF, called __________________, has a __________________ effect on MPF activity and plays a part in regulating interactions with its __________________s.

cyclin stimulatory substrates

18-32 The cell-cycle control system relies on sharp increases in the activities of regulatory proteins called __________________, or __________________, to trigger S phase and M phase. Inactivation of __________________ is required to exit from M phase after chromosome segregation.

cyclin-dependent kinases Cdks M-Cdk

how does necrosis happen?

cytoplasm leaks out and inflammation occurs

18-41 Which word or phrase below best describes the phase in mitosis depicted in Figure Q18-41? (a) anaphase (b) prometaphase (c) S-phase checkpoint (d) metaphase

18-19 MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which of the following statements is not a legitimate conclusion from the control experiment? (a) The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation. (b) An increased volume of cytoplasm is insufficient to cause mitotic spindle formation. (c) Injection of extra RNA molecules is insufficient to cause mitotic spindle formation. (d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation.

d (COMPONENTs of an interphase nucleus are insufficient to cause mitotic spindle formation)

18-55 Which of the following statements is true? (a) Anaphase A must be completed before anaphase B can take place. (b) In cells in which anaphase B predominates, the spindle will elongate much less than in cells in which anaphase A dominates. (c) In anaphase A, both kinetochore and interpolar microtubules shorten. (d) In anaphase B, microtubules associated with the cell cortex shorten.

d (In anaphase B, microtubules associated with the cell cortex shorten)

18-17 Which of the following statements is false? (a) Mitotic Cdk must be phosphorylated by an activating kinase (Cak) before it is active. (b) Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive, even if it is phosphorylated by the activating kinase. (c) Active M-Cdk phosphorylates the activating phosphatase (Cdc25) in a positive feedback loop. (d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active.

d (the activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active)

16-36 Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure Q16-36. Figure Q16-36 Which of the following statements is false? (a) A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase. (b) A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor. (c) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available. (d) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.

d (a constitutevely active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of GLYCOGEN available)

18-56 When introduced into mitotic cells, which of the following is expected to impair anaphase B but not anaphase A? (a) an antibody against myosin (b) ATPγS, a nonhydrolyzable ATP analog that binds to and inhibits ATPases (c) an antibody against the motor proteins that move from the plus end of microtubules to the minus end (d) an antibody against the motor proteins that move from the minus end of microtubules toward the plus end

d (an antibody against the motor proteins that move from the minus end of microtubules toward the plus end)

18-67 Which of the following statements about apoptosis is true? (a) Cells that constitutively express Bcl2 will be more prone to undergo apoptosis. (b) The prodomain of procaspases contains the catalytic activity necessary for procaspase activation. (c) Bax and Bak promote apoptosis by binding to procaspases in the apoptosome. (d) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria

d (apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria)

18-5 In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated? (a) at the transition between G1 and S (b) when cells enter G0 (c) during M (d) at the end of G2

d (cells check to determine whether the DNA is fully and correctly replicated at the end of G2)

18-12 Levels of Cdk activity change during the cell cycle, in part because ________________. (a) the Cdks phosphorylate each other. (b) the Cdks activate the cyclins. (c) Cdk degradation precedes entry into the next phase of the cell cycle. (d) cyclin levels change during the cycle. d (cyclin levels change during the cycle)

d (cyclin levels change during the cycle)

16-6 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 (delta is involved in CONTACT-DEPENDENT signaling)

16-10 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)

16-58 Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2, as diagrammed in Figure Q16-58. Figure Q16-58 Which of the following statements is false? (a) In the presence of a survival signal, Akt is phosphorylated. (b) In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2. (c) In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active. (d) In the absence of a survival signal, Bad is phosphorylated.

d (in the absence of a survival signal, bad is phosphorylated)

16-11 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)

18-25 The G1 DNA damage checkpoint ________________. (a) causes cells to proceed through S phase more quickly. (b) involves the degradation of p53. (c) is activated by errors caused during DNA replication. (d) involves the inhibition of cyclin-Cdk complexes by p21.

d (involves the inhibition of cyclin-Cdk complexes by p21.)

18-63 Which of the following statements is false? (a) Cytokinesis in plant cells is mediated by the microtubule cytoskeleton. (b) Small membrane vesicles derived from the Golgi apparatus deliver new cell-wall material for the new wall of the dividing cell. (c) The phragmoplast forms from the remains of interpolar microtubules of the mitotic spindle. (d) Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall. d (motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall)

d (motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall)

18-48 Disassembly of the nuclear envelope ________________. (a) causes the inner nuclear membrane to separate from the outer nuclear membrane. (b) results in the conversion of the nuclear envelope into protein-free membrane vesicles. (c) is triggered by the phosphorylation of integrins. (d) must occur for kinetochore microtubules to form in animal cells.

d (must occur for kinetochore microtubules to form in animal cells)

16-31 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 Gα separates from Gβγ. (d) the GTPase activity of Gα.

d (the GTPase activity of Galpha)

18-2 What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? (a) Cells would not be able to replicate their DNA. (b) The mitotic spindle could not assemble. (c) Cells would get larger and larger. (d) The cells produced would get smaller and smaller.

d (the cells produced would get smaller and smaller)

18-62 Which of the following statements is false? (a) The cleavage furrow is a puckering of the plasma membrane caused by the constriction of a ring of filaments attached to the plasma membrane. (b) The cleavage furrow will not begin to form in the absence of a mitotic spindle. (c) The cleavage furrow always forms perpendicular to the interpolar microtubules. (d) The cleavage furrow always forms in the middle of the cell.

d (the cleavage furrow always forms in the MIDDLE of the cell)

16-30 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)

18-36 Which of the following statements is true? (a) The mitotic spindle is largely made of intermediate filaments. (b) The contractile ring is made largely of microtubules and actin filaments. (c) The contractile ring divides the nucleus in two. (d) The mitotic spindle helps segregate the chromosomes to the two daughter cells.

d (the mitotic spindle helps segregate the chromosomes to the two daughter cells)

18-20 Which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution? (a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle. (b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans. (c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast. (d) Yeast cells have only one Cdk, whereas humans have many Cdks.

d (yeast cells have only one Cdk, whereas humans have many Cdks)

All members of the steroid hormone receptor family: a.) are cell-surface receptors. b.) do not undergo conformational changes upon steroid hormone binding. c.) are found exclusively in the cytoplasm. d.) interact with signal molecules that diffuse through the plasma membrane. e.) result in very rapid changes in cellular behavior upon steroid hormone binding.

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

16-33 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 to the external environment of the cell

decrease decrease increase decrease decrease decrease

Do all cells types respond to acetylcholine similarly or differently?

differently

enzyme coupled receptors

discovered for their role in responding to growth factors in animal cells

18-42 Which letter is associated with the line that is pointing to the interpolar microtubules in Figure Q18-41? (a) A (b) B (c) C (d) D (e) E

18-18 Many features of __________________ cells make them suitable for biochemical studies of the cell-cycle control system. For example, the cells are unusually large and are arrested in a __________________-like phase. When the cells are triggered to resume cycling, the cell divisions have especially __________________ G1 and G2 phases and occur __________________.

egg G2 short synchronously

16-2 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.

endocrine; contact-dependent;

3 main classes of cell surface receptors

enzyme coupled receptors ion channel coupled receptors G protein coupled receptors

what are caspases?

enzymes that program cell death

all cell surface receptor proteins bind to a(n) _____________ and transduce its message into one or more intracellular signaling molecules that alter the cell's behavior

extracellular signal molecule

18-45 Before chromosomes segregate in M phase, they and the segregation machinery must be appropriately prepared. Indicate whether the following statements are true or false. If false, change a single noun to make the statement true. A. Sister chromatids are held together by condensins from the time they arise by DNA replication until the time they separate at anaphase. B. Cohesins are required to make the chromosomes more compact and thus to prevent tangling between different chromosomes. C. The mitotic spindle is composed of actin filaments and myosin filaments. D. Microtubule-dependent motor proteins and microtubule polymerization and depolymerization are mainly responsible for the organized movements of chromosomes during mitosis. E. The centromere nucleates a radial array of microtubules called an aster, and its duplication is triggered by S-Cdk. F. Each centrosome contains a pair of centrioles and hundreds of γ-tubulin rings that nucleate the growth of microtubules.

false false false false true

the number of different types of receptors is ______ than the number of extracellular signals that act on them

greater

16-37 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 higher lower lower

reactions that do not involve changes in gene transcription or new protein synthesis occur where?

in the cytosol

18-46 Before mitosis, the number of centrosomes must [increase/decrease]. At the beginning of [anaphase/prophase] in animal cells, the centrosomes separate in a process driven partly by interactions between the [plus/minus] ends of microtubules arising from the two centrosomes. Centrosome separation initiates the assembly of the bipolar mitotic spindle and is associated with a sudden [increase/decrease] in the dynamic instability of microtubules.

increase prophase plus increase

what does myostatin do?

inhibits muscle formation

foreign substances like nicotine, morphine, and methanol exert their initial effects by...

interacting with cell surface receptors causing the receptors to transduce signal inappropriately in the absence of the normal stimulus

The enzyme responsible for transfer of a phosphoryl group from a high energy donor to a suitable substrate is known as a:

kinase

18-46 In comparison with an interphase microtubule array, a mitotic aster contains a [smaller/larger] number of [longer/shorter] microtubules. Extracts from M-phase cells exhibit [increased/decreased/unchanged] rates of microtubule polymerization and increased frequencies of microtubule [shrinkage/growth].

larger shorter unchanged shrinkage

Ca+ can trigger biological effects in cells because an unstimulated cell has an extremely --------concentration of free Ca+ in the cystosol, compared with its concentration in the ----------space in the --------creating a steep elctrochemical gradient. when Ca+ enters the cystosol, it interacts with Ca+ responsive such as ------which also binds to diacylglcerol and --------which activates CAM kinases

low extracellular ER PKC calmodulin

16-44Ca2+ 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

low; extracellular; endoplasmic reticulum

18-18 Studies with Xenopus eggs identified a partly purified activity called __________________ that drives a resting Xenopus oocyte into M phase. MPF activity was found to __________________ during the cell cycle, although the amount of its kinase component, called __________________, remained constant.

maturation promoting factor oscillate Cdk

18-71 . One class of signal molecules, called __________________, stimulates cell division by releasing the molecular brakes that keep cells in the __________________ or __________________ phase of the cell cycle. Members of a second class of signal molecules are called __________________, because they stimulate cell growth and an increase in cell mass.

mitogens G0 G1 growth factors

16-28 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

GTPase-activating proteins (GAPs) stimulate the hydrolysis of GTP to GDP. does it switch on or off?

off

guanine nucleotide exchange factors (GEFs) promote the exchange of GDP to GTP. does it switch on or off?

16-2 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.

paracrine; neuronal; receptor

at the start of the pathway both the a subunit and by subunit of the G protein Gq are involved in activating __________. two smaller messenger molecules __and ___ are produced. when a membrane ______ is hydrolyzed by activated phospholipase c, inositol 1,4,5-triphopsphate (IP3) diffuses through the cytosol the triggers the release of _____ from the ER by binding to and opening special _____ channels in the ER membrane. the large electrochemical gradient for ____ across this membrane causes ____ to rush out of the ER and into the cytosol. ______ remains in the plasma membrane and, together with Ca2+, helps activate the enzyme ____ which is recruited from the cytosol to the cytosolic face of the plasma membrane. _____ then phosphorylates its own set of intracellular proteins, further propagating the signal

phospholipase c IP3 DAG inositol phospholipase Ca++ Ca++ Ca++ Ca++ DAG PKC PKC

At the start of the pathway both alpha subunit and the beta(y) subunit of the G-PROTEIN (Gq) are invovled in activating --------. two small messenger molecules ------and --------are produced. when a membrane ----------is hydrolyzed by activated phospholipase C, inistol 1,4,5-triphosphate (IP3) diffucses through the cystol and triggers the release of ------from the ER BY THE BINDING TO AND OPENING ------CHANNELS IN THE ER MEMBRANE. ----------then phosphorylates its own set of intracellular proteins further propagating the signal

phospholipase c IP3 and DAG inositol phospholipid Ca+ ion Ca+ PKC

Indicate whether the following molecules are found in plants, animals, or both. Cell wall

plants

Indicate whether the following molecules are found in plants, animals, or both. Cellulose

plants

the action of CA+ in a second messenger scheme -------

produces sustained responses by controlling the flow of Ca+ into the cell

18-71 The survival, __________________, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface __________________ and trigger various intracellular signaling pathways.

proliferation receptor

cyclic amp exerts its effects in animals cells mainly by activating the enzyme ------- which catalyzes the transfer of the terminal phospahate group from the ATP to specific serines or threonines of selected proteins

protein kinase

16-44 When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as __________________, which also binds diacylglycerol, and __________________, which activates CaM-kinases.

protein kinase Cl calmodulin

16-19 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.

receptors; effector

18-46 The changes in microtubule dynamics are largely due to [enhanced/reduced] activity of microtubule-associated proteins and [increased/decreased] activity of catastrophins. The new balance between polymerization and depolymerization of microtubules is necessary for the mitotic spindle to move the [replicated chromosomes/daughter chromosomes] to the metaphase plate.

reduced increased replicated chromosomes

18-71 The third class of signal molecules, called __________________, inhibits __________________ by regulating members of the __________________ family of proteins. In addition to such stimulatory factors, some signal proteins such as __________________ act negatively on other cells, inhibiting their survival, growth, or proliferation.

survival factors apoptosis Bc12 myostatin

some very rare individuals are genetically male but lack the testosterone receptor. what happens in individuals who lack the receptor for the male sex hormone testosterone?

they make testosterone but their cell cannot respond to it. as a result, these individuals develop as females

All of the following are true about heterotrimeric G proteins EXCEPT: - A. They bind either GDP or GTP. - B. They have GTPase activity. - C. They act as binary (on-off) switches. - D. They help amplify a hormone's signal. - E. They phosphorylate proteins.

they phosphorylate proteins

18-51 Is the following statement true or false? After the nuclear envelope breaks down, microtubules gain access to the chromosomes and, every so often, a randomly probing microtubule captures a chromosome and ultimately connects to the kinetochore to become a kinetochore microtubule of the spindle.

true

G-proteins and monomeric GTPase are active when GTP is bound but inactive when GDP is bound (true or false)

true

18-7 Are the statements below true or false? Explain your answer. A. Statement 1: Generally, in a given organism, the S, G2, and M phases of the cell cycle take a defined and stereotyped amount of time in most cells. B. Statement 2: Therefore, the cell-cycle control system operates primarily by a timing mechanism, in which the entry into one phase starts a timer set for sufficient time to complete the required tasks. After a given amount of time has elapsed, a molecular "alarm" triggers movement to the next phase.

true false

GPCRs mediate responses to an enormous diversity of extracellular signal molecules and are involved in a large variety of cell process (true or false)

true (they are attractive target for the development of drugs to treat many disorders)

16-27 __________________ 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.

two; GDP; GTP

The figure shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine?

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

Which of the following is not a general mechanism of cell memory? • (a) a positive feedback loop, mediated by a transcriptional regulator that activates transcription of its own gene in addition to other cell-type specific genes • (b) inheritance of histone modification patterns when cells divide • (c) proper segregation of housekeeping proteins when cells divide • (d) inheritance of DNA methylation patterns when cells divide

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