MCC_Exam 4

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. 17-5 Rank the following cytoskeletal filaments from smallest to largest in diameter (1 = smallest in diameter, 4 = largest) ______ intermediate filaments ______ microtubules ______ actin filament ______ myofibril

2, 3, 1, 4

. 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

3, 1, 2, 4

. 19-17 Meiosis is a highly specialized cell division in which several events occur in a precisely defined order. Please order the meiotic events listed below. 1. loss of cohesins near centromeres 2. chromatid pairing 3. chromosome condensation 4. chromosome replication 5. degradation of cohesins bound to chromosome arms 6. formation of chiasmata (chiasmata = plural of chiasma) 7. homolog pairing 8. alignment of chromosomes at the metaphase plate

4, 2, 7, 6, 3, 8, 5, 1

. 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

A. Decrease B. Decrease C. Increase D. Decrease E. Decrease F. Decrease

. 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.

A. False B. False C. False D. True E. False F. True

. 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.

A. G1 arrest B. neither C. both D. S-phase arrest

. 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.

A. No B. Yes C. Yes D. No E. Yes

. 17-3 Indicate which of the three major classes of cytoskeletal elements each statement below refers to. A. monomer that binds ATP B. includes keratin and neurofilaments C. important for formation of the contractile ring during cytokinesis D. supports and strengthens the nuclear envelope E. their stability involves a GTP cap F. used in the eukaryotic flagellum G. a component of the mitotic spindle H. can be connected through desmosomes I. directly involved in muscle contraction J. abundant in filopodia

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

. 18-43 Before a cell can enter M phase, two structures from Figure Q18-41 must be duplicated. Write the letters corresponding to the lines pointing to these structures, and write the names of the structures next to the letters.

A. centrosomes, B. chromosome

. 17-38 Indicate whether each of the following statements refers to a ciliary microtubule, a microtubule of the mitotic spindle, both types of microtubule, or neither type of microtubule. A. The basal body is the organizing center. B. The monomer is sequestered by profilin. C. It is arranged in a "9 + 2" array. D. It is nucleated at the centrosome. E. It uses dynein motors. F. It is involved in sperm motility. G. It is involved in moving fluid over the surface of cells.

A. ciliary microtubules B. neither C. ciliary microtubules D. microtubules of the mitotic spindle E. both F. neither G. ciliary microtubules

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

A. higher B. higher C. lower D. lower

. 19-13 Indicate whether each of the following is true for meiosis, mitosis, both, or neither. A. formation of a bivalent B. genetically identical products C. condensation of chromosomes D. segregation of all paternal chromosomes to one cell E. involvement of DNA replication

A. meiosis B. mitosis C. both D. neither E. both

16-51 You are interested in cell-size regulation and discover that signaling through an enzyme-coupled receptor is important for the growth (enlargement) of mouse liver cells. Activation of the receptor activates adenylyl cyclase, which ultimately leads to the activation of PKA, which then phosphorylates a transcription factor called TFS on threonine 42. This phosphorylation is necessary for the binding of TFS to its specific sites on DNA, where it then activates the transcription of Sze2, a gene that encodes a protein important for liver cell growth. You find that liver cells lacking the receptor are 15% smaller than normal cells, whereas cells that express a constitutively activated version of PKA are 15% larger than normal liver cells. Given these results, predict whether you would expect the cell's size to be bigger or smaller than normal cells if cells were treated in the following fashion. A. You change threonine 42 on TFS to an alanine residue. B. You create a version of the receptor that is constitutively active. C. You add a drug that inhibits adenylyl cyclase. D. You add a drug that increases the activity of cyclic AMP phosphodiesterase. E. You mutate the cAMP-binding sites in the regulatory subunits of PKA, so that the complex binds cAMP more tightly.

A. smaller B. Bigger C. Smaller D. Smaller E. Bigger

18-47 Match each of the main classes of spindle microtubules from list 1 with their functions and features from list 2. List 1 (A) Interpolar microtubules (B) Aster microtubules (C) Kinetochore microtubules List 2 1. Stabilized by interactions with each other via motor proteins 2. Interact with the cell cortex 3. Link chromosomes to a spindle pole 4. Depolymerize to promote anaphase A 5. Depolymerize to promote anaphase B

A—1, B—2, 5, C—3,4

. 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, D—2, E—4

. 17-36 Match the following labels to the numbered lines on Figure Q17-36. Figure Q17-36 A. minus end of microtubule B. tail of motor protein C. cargo of motor protein D. head of motor protein . Which of the two motors in Figure Q17-36 is most probably a kinesin? Explain your answer.

A—4, B—2, C—1, D—3, the top motor

18-10 Match the following labels to the numbered label lines on Figure Q18-10. A. G1 phase B. mitotic cyclin C. mitotic Cdk D. S phase E. S-phase cyclin F. S-phase Cdk G. MPF H. G2 phase

A—5, B—6, C—3, D—2, E—4, F—1, G—7, H—8

. 19-22 Imagine a diploid sexually reproducing organism, Diploidus sexualis, that contains three pairs of chromosomes. This organism is unusual in that no recombination between homologous chromosomes occurs during meiosis. A. Assuming that the chromosomes are distributed independently during meiosis, how many different types of sperm or egg cells can a single individual of this species produce? B. What is the likelihood that two siblings of this species will be genetically identical? You can assume that the homologous chromosomes of each parent are different from one another and from their counterparts in the other parent.

A—8, B—1/64

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

. 16-43 Match the target of the G protein with the appropriate signaling outcome. adenylyl cyclase ________ ion channels _________ phospholipase C _________ cleavage of inositol phospholipids increase in cAMP levels 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

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

B-tubulin, a-tubulin, thirteen, y-tubulin, centrosome, GTP, basal body, nine, dynein

. 16-14 Can signaling via a steroid hormone receptor lead to amplification of the original signal? If so, how?

Because the interactions of the signal molecule with its receptor and of the activated receptor with its gene are both one-to-one, there is no amplification in this part of the signaling pathway. The signal can, however, be amplified when the target genes are transcribed, because each activated gene produces multiple copies of mRNA, each of which is used to make multiple copies of the protein that the gene encodes.

17-12 Match the type of intermediate filament with its appropriate location. lamins _________ neurofilaments _________ vimentins _________ keratins _________ nerve cells B. epithelia C. nucleus D. connective tissue

C, A, D, B

. 17-43 Actin can adopt a variety of shapes. Match the name of the actin form with the type of actin structure depicted as black lines within the cells in Q17-43. _____ lamellipodia _____ contractile bundles _____ contractile ring _____ microvilli

C, B, D,A

. 17-17 Place the following in order of size, from the smallest to the largest. protofilament microtubule α-tubulin tubulin dimer E. mitotic spindle

C, D,A,B,E

. 17-51 The following proteins are important for cell movement. Match the following proteins with their function. A. nucleation of new actin filaments at the side of an existing filament B. regulation of the availability of actin monomers C. important for the growth of straight, unbranched actin filaments D. contracting the rear of the cell E. involvement in focal contacts myosin_________ ARP proteins________ profilin_________ integrins________ formins__________

D,A,B,E,C

. 19-56 Do you agree or disagree with the following statement? Explain your answer. A trait that is found at a low frequency in the population has to be a recessive trait.

Disagree

. 19-45 Is the following statement true or false? Explain. The phenotype of an organism reflects all of the alleles carried by that individual.

False

. 16-21 Match the class of cell-surface receptor with the best description of its function. Not all descriptors will be used. G-protein-coupled receptors ______ ion-channel-coupled receptors ______ enzyme-coupled receptors ______ A. alter the membrane potential directly by changing the permeability of the plasma membrane B. signal by opening and closing in a ligand-independent manner C. must be coupled with intracellular monomeric GTP-binding proteins D. all receptors of this class are polypeptides with seven transmembrane domains E. discovered for their role in responding to growth factors in animal cells

G-protein-coupled receptors - > D ion-channel-coupled receptors -> A enzyme-coupled receptors -> E

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

M phase, interphase, G1 phase, S phase, G2 phase, mitosis, cytokinesis, cyclin-dependent kinases, Cdks, M-Cdk

17-62 Kinesins were purified by adding the nonhydrolyzable analog AMP-PNP to cytoplasmic extracts containing microtubules, purifying the microtubules, and then releasing the kinesin proteins, which were still attached to the microtubules, by adding ATP. Would this trick have worked to purify myosin motors attached to actin filaments? Explain.

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

NO, JAKs, STATs, MAP kinase, diacylglycerol, IP3

The four phases of the cell cycle, in order, are G1, __________________, __________________, and __________________. A cell contains the most DNA after __________________ phase of the cell cycle. A cell is smallest in size after __________________ phase of the cell cycle. Growth occurs in __________________, __________________, and __________________ phases of the cell cycle. A cell does not enter mitosis until it has completed __________________ synthesis.

S, G2, M, S, M, G1, S, G2, DNA

. 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.

T, F

. 16-48 Antibodies are Y-shaped molecules that have two identical binding sites. Suppose that you have obtained an antibody that is specific for the extracellular domain of an RTK. When the antibody binds to the RTK, it brings together two RTK molecules. If cells containing the RTK were exposed to the antibody, would you expect the kinase to be activated, inactivated, or unaffected? Explain your reasoning.

The RTK will probably become activated on binding of the antibody molecule. This is because signal-induced dimerization usually activates RTKs. When RTK molecules are brought together, their cytoplasmic kinase domains become activated and each receptor phosphorylates the other.

. 16-41 Activated GPCRs activate G proteins by reducing the strength of binding of GDP to the α subunit of the G protein, allowing GDP to dissociate and GTP (which is present at much higher concentrations in the cell than GDP) to bind in its place. How would the activity of a G protein be affected by a mutation that reduces the affinity of the α subunit for GDP without significantly changing its affinity for GTP?

The mutant G protein would be constantly active. Each time the α subunit hydrolyzed GTP to GDP, the GDP would dissociate spontaneously, allowing GTP to bind and reactivate the α subunit, especially because the intracellular concentration of GTP is higher than that of GDP. Normally, GDP is tightly bound by the α subunit, which keeps the G protein in its inactive state until interaction with an appropriate activated GPCR stimulates the release of GDP.

. 16-4 Explain why the signal molecules used in neuronal signaling work at a longer range than those used in contact-dependent signaling.

The neurotransmitter released from a neuron in neuronal signaling must diffuse across the synaptic cleft to reach receptors on the target cell. In contrast, in contact-dependent signaling, the signal molecule is attached to the plasma membrane of the signaling cell and interacts with receptors located on the plasma membrane of the receiving cell; thus, the cells must be in direct contact for this type of signaling to occur.

. 16-24 Intracellular steroid hormone receptors have binding sites for a signaling molecule and a DNA sequence. How is it that the same steroid hormone receptor, which binds to a specific DNA sequence, can regulate different genes in different cell types?

The specific genes regulated in response to an activated steroid hormone receptor depends not only on the genes having the appropriate DNA sequence for binding the receptor but also on a variety of other nuclear proteins that influence gene expression, some of which vary between different cell types.

. 16-64 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? Why?

These mice will have dark brown fur. The inability to hydrolyze GTP to GDP will lead to inappropriate activation of the signaling pathway that makes pigment. Too much pigment will be produced, as seen in the mice lacking cAMP phosphodiesterase (which lack the ability to damp the signal), and the mice will end up with dark brown fur.

. 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

. 19-11 Is the following statement true or false? Explain. Somatic cells leave no progeny and thus, in an evolutionary sense, exist only to help create, sustain, and propagate the germ cells.

True

. 16-22 Which of the following statements is true? . (a) Extracellular signal molecules that are hydrophilic must bind to a cell- surface receptor so as to signal a target cell to change its behavior. . (b) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. . (c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. . (d) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.

. 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.

. 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

. 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

. 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

. 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

. 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 ethylene- responsive 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.

. 17-20 Which of the following statements about the function of the centrosome is false? . (a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome. . (b) Centrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation. . (c) Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules. . (d) Centrosomes are the major microtubule-organizing center in animal cells.

. 17-21 Which of the following statements about microtubules is true? . (a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. . (b) The centromere nucleates the microtubules of the mitotic spindle. . (c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. . (d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.

. 17-29 Which of the situations below will enhance microtubule shrinkage? . (a) addition of a drug that inhibits GTP exchange on free tubulin dimers . (b) addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers . (c) addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules . (d) addition of a drug that blocks the ability of a tubulin dimer to bind to γ- tubulin

. 17-31 The graph in Figure Q17-31 shows the time course of the polymerization of pure tubulin in vitro. Assume that the starting concentration of free tubulin is higher than it is in cells. Figure Q17-31 Three parts of the curve are labeled above it as A, B, and C. You conduct a similar in vitro tubulin-polymerization experiment, only you include purified centrosomes in your preparation. When you plot your data, which part of your graph should be most dissimilar to the curve shown in Figure Q17-31? . (a) A . (b) B . (c) C . (d) None. The shape of my graph should be identical to the graph produced when tubulin is polymerized in the absence of purified centrosomes.

. 17-39 Which of the following items is not important for flagellar movement? . (a) sarcoplasmic reticulum . (b) ATP . (c) dynein . (d) microtubules

. 17-46 Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments? . (a) Actin filaments would grow longer. . (b) Actin filaments would grow shorter because depolymerization would be enhanced. . (c) Actin filaments would grow shorter because new monomers could not be added to the filaments. . (d) No change, as addition of monomers binding nonhydrolyzable ATP would not affect actin filament length.

. 17-8 All intermediate filaments are of similar diameter because ____________. (a) the central rod domains are similar in size and amino acid sequence. (b) the globular domains are similar in size and amino acid sequence. (c) covalent bonds among tetramers allow them to pack together in a similar fashion. (d) there is only a single type of intermediate filament in every organism.

. 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.

. 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.

. 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

. 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.

. 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

. 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

. 18-61 Cytokinesis in animal cells ________________. . (a) requires A TP . . (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.

. 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.

. 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.

. 19-2 Which of the following statements is true? . (a) Another name for the fertilized egg cell is the zygote. . (b) Diploid organisms reproduce only sexually. . (c) All sexually reproducing organisms must have two copies of every chromosome. . (d) Gametes have only one chromosome.

. 19-25 Which of the following statements about meiosis is true? . (a) During meiosis, the paternal chromosomes pair with the maternal chromosomes before lining up at the metaphase plate. . (b) Unicellular organisms that have a haploid state undergo meiosis instead of mitosis during cell division. . (c) Meiosis produces four genetically identical cells. . (d) In general, meiosis is faster than mitosis.

. 19-35 During fertilization in humans, _______________________. (a) a wave of Ca2+ ions is released in the fertilized egg's cytoplasm. (b) only one sperm binds to the unfertilized egg. (c) a sperm moves in a random fashion until it encounters an egg. (d) several sperm pronuclei compete in the cytoplasm to fuse with the egg nucleus.

. 19-39 If you crossed the round-seeded plants obtained in the F1 generation with a true- breeding strain of round-seeded plants, how many wrinkle-seeded plants would you expect to obtain in the next generation? (See Figure Q19-38.) . (a) none . (b) 25% . (c) 75% . (d) all

. 19-42 Which of the following statements about the experiment diagrammed in Figure Q19-38 is true? . (a) If you crossed all the round-seeded pea plants from the F2 generation with true-breeding wrinkle-seeded pea plants, you would get more round- seeded pea plants in the next generation than if you crossed all the round- seeded pea plants from the F1 generation with true-breeding wrinkle- seeded pea plants. . (b) The reason you do not see wrinkle-seeded pea plants in the F1 generation is because the round-seeded pea plants used to create the F1 generation were not true-breeding strains. . (c) The gene for round-seeded pea plants is on a different chromosome from the gene for wrinkle-seeded pea plants, which is why you get 25% wrinkle-seeded pea plants in the F2 generation. . (d) If you crossed the round-seeded pea plants from the F2 generation with the wrinkle-seeded pea plants from the F2 generation, you should get 100% round-seeded pea plants.

. 19-44 Which of the following reasons was essential for Mendel's law of independent assortment? . (a) All the traits that Mendel examined involved genes that did not display linkage. . (b) Several of the phenotypes that Mendel examined involved color. . (c) Mendel observed chromosomal segregation in pea-plant cells. . (d) Mendel carried out his experiments on plants and not on fungi.

. 19-5 Which of the following statements about the benefits of sexual reproduction is false? . (a) Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially during fertilization. . (b) Unicellular organisms that can undergo sexual reproduction have an increased ability to adapt to harsh environments. . (c) Sexual reproduction reshuffles genes, which is thought to help species survive in novel or varying environments. . (d) Sexual reproduction can speed the elimination of deleterious alleles.

. 19-9 Both budding yeast and the bacteria E. coli are unicellular life. Which of the following statements explains why budding yeast can undergo sexual reproduction while E. coli cannot. . (a) Unlike E. coli, budding yeast can alternate between a diploid state and a haploid state. . (b) Unlike E. coli, budding yeast cannot multiply by undergoing cell division. . (c) Unlike E. coli, haploid budding yeast cells can undergo meiosis to produce the gametes necessary for sexual reproduction. . (d) E. coli DNA is unable to undergo homologous recombination, making it incapable of producing gametes.

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.

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

. 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.

. 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.

. 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

. 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 inactiveeither 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

. 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

. 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.

. 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

. 17-9 Intermediate filaments help protect animal cells from mechanical stress because ____________. . (a) filaments directly extend from the interior of the cell to the extracellular space and into the next cell, linking one cell to the next, helping to distribute locally applied forces. . (b) filaments in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells. . (c) filaments remain independent of other cytoskeletal elements and keep the mechanical stress away from other cellular components. . (d) filaments make up the desmosome junctions that connect cells; these junctions are more important than the internal network of filaments for protecting cells against mechanical stress.

. 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

. 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.

. 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.

. 16-59 The last common ancestor to plants and animals was a unicellular eukaryote. Thus, it is thought that multicellularity and the attendant demands for cell communication arose independently in these two lineages. This evolutionary viewpoint accounts nicely for the vastly different mechanisms that plants and animals use for cell communication. Fungi use signaling mechanisms and components that are very similar to those used in animals. Which of the phylogenetic trees shown in Figure Q16-59 does this observation support? Figure Q16-59

. 17-10 Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-10 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose α-helical region is twice as long as that of a normal intermediate filament by duplicating the normal α-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFαd. If you were to assemble intermediate filaments using IFαd as the subunit, which of the following predictions describes the most likely outcome? Figure Q17-10 . (a) Filaments assembled using IFαd will interact with different cytoskeletal components. . (b) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments. (c) Sixteen tetramers assembled from IFαd will be needed for a ropelike structure to form. (d) Dimers of IFαd will form by interactions with the N-terminal globular head and the C-terminal globular tail.

. 17-26 You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________________. . (a) MtA is involved in stabilizing microtubules. . (b) MtA binds to GTP-bound tubulin on microtubules. . (c) MtA is important for the interaction of microtubules with the centrosome. . (d) MtA will not bind to purified microtubules in a test tube.

. 17-32 Which of the following statements about organellar movement in the cell is false? . (a) Organelles undergo saltatory movement in the cell. . (b) Only the microtubule cytoskeleton is involved in organellar movement. . (c) Motor proteins involved in organellar movement use ATP hydrolysis for energy. . (d) Organelles are attached to the tail domain of motor proteins.

. 17-44 Consider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules? . (a) Although both filaments can grow from both ends, the growth rate is faster at the plus ends. . (b) Depolymerization initiates at the plus ends of filaments. . (c) Nucleotide hydrolysis promotes depolymerization of filaments. . (d) Free subunits (actin and tubulin) carry nucleoside triphosphates.

. 17-49 Which of the following statements is false? . (a) Cytochalasins prevent actin polymerization. . (b) Actin filaments are usually excluded from the cell cortex. . (c) Integrins are transmembrane proteins that can bind to the extracellular matrix. . (d) ARPs can promote the formation of branched actin filaments.

. 17-57 Figure Q17-57shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled. Figure Q17-57 Which of the following statements is true about muscle contraction? . (a) Point A will move closer to point B. . (b) Point B will move closer to point C. . (c) Region D will become smaller. . (d) Region E will shrink in size.

. 17-58 Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction? . (a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero . (b) addition of a drug that blocks Ca2+ binding to troponin . (c) an increase in the amount of ATP in the cell . (d) a mutation in tropomyosin that decreases its affinity for the actin filament

. 17-59 Which of the following statements about skeletal muscle contraction is false? . (a) When a muscle cell receives a signal from the nervous system, voltage- gated channels open in the T-tubule membrane. . (b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction. . (c) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. . (d) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.

. 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.

. 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

. 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 S- Cdk. . (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.

. 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

. 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.

. 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.

. 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.

. 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.

. 19-14 The formation of a bivalent during meiosis ensures that _______. . (a) one chromatid from the mother and one chromatid from the father will segregate together during meiosis I. . (b) all four sister chromatids remain together until the cell is ready to divide. . (c) recombination will occur between identical sister chromatids. . (d) the sex chromosomes, which are not identical, will line up separately at the metaphase plate during meiosis I.

. 19-21 A diploid cell containing 32 chromosomes will make a haploid cell containing ___ chromosomes. . (a) 8 . (b) 16 . (c) 30 . (d) 64

. 19-27 During recombination ________________________. . (a) sister chromatids undergo crossing-over with each other. . (b) chiasmata hold chromosomes together. . (c) one crossover event occurs for each pair of human chromosomes. . (d) the synaptonemal complex keeps the sister chromatids together until anaphase II.

. 19-28 After the first meiotic cell division ________________________. . (a) two haploid gametes are produced. . (b) cells are produced that contain the same number of chromosomes as somatic cells. . (c) the number of chromosomes will vary depending on how the paternal and maternal chromosomes align at the metaphase plate. . (d) DNA replication occurs.

. 19-3 Which of the following statements is false? . (a) Asexual reproduction typically gives rise to offspring that are genetically identical. . (b) Mutations in somatic cells are passed on to individuals of the next generation. . (c) Sexual reproduction allows for a wide variety of gene combinations. . (d) Gametes are specialized sex cells.

. 19-31 In mammals, there are two sex chromosomes, X and Y, which behave like homologous chromosomes during meiosis. Normal males have one X chromosome and one Y chromosome, and normal females have two X chromosomes. Males with an extra Y chromosome (XYY) are found occasionally. Which of the following could give rise to such an XYY male? Explain your answer. . (a) nondisjunction in the first meiotic division of spermatogenesis normal meiosis in the mother . (b) nondisjunction in the second meiotic division of spermatogenesis; normal meiosis in the mother . (c) nondisjunction in the first meiotic division of oogenesis; normal meiosis in the father . (d) nondisjunction in the second meiotic division of oogenesis; normal meiosis in the father

. 19-38 Which of the following could be considered a true-breeding strain for the seed- shape phenotype? (See Figure Q19-38.) . (a) all of the round-seeded plants produced in the F2 generation . (b) all of the wrinkle-seeded plants produced in the F2 generation . (c) all of the round-seeded plants produced in the F1 generation . (d) half of the round-seeded plants produced in the F2 generation

. 19-40 If you crossed the round-seeded plants obtained in the F1 generation with a true- breeding strain of wrinkle-seeded plants, how many round-seeded plants would you expect to obtain in the next generation? (See Figure Q19-38.) . (a) 25% . (b) 50% . (c) 75% . (d) 100%

. 19-58 Haplotype blocks can be seen in humans because _______. . (a) disease genes are found in haplotype blocks. . (b) modern humans descended from a relatively small population of about 10,000 individuals that existed about two thousand generations ago. . (c) some of our human ancestors interbred with Neanderthals. . (d) new mutations cannot be introduced into existing haplotype blocks.

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

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. 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.

. 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 is true

. 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, fibroblasts, and nerve cells must all have the same receptor for QGF.

. 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.

. 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.

. 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.

. 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

. 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

. 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.

. 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

. 17-15 You are studying nuclear lamins in yeast. Using recombinant DNA technology, you alter the coding sequence of a nuclear lamin gene such that the gene now codes for a nuclear lamin protein that can no longer be phosphorylated when the nuclear envelope is broken down during mitosis. What do you predict would happen if the yeast cell only had the altered nuclear lamin gene (and not the unaltered version)? . (a) Mitosis should proceed as usual because the dephosphorylation of the lamin is what is important for nuclear lamina assembly during mitosis, so phosphorylation will not be necessary. . (b) Disassembly of the nuclear lamins will occur prematurely because the lamins cannot be phosphorylated. . (c) Nuclear lamins will no longer disassemble properly during mitosis. . (d) Nuclear lamins will be unable to produce dimers, as coiled-coil formation will be disrupted.

. 17-2 Which of the following statements about the cytoskeleton is false? . (a) The cytoskeleton is made up of three types of protein filaments. . (b) The cytoskeleton controls the location of organelles in eukaryotic cells. . (c) Covalent bonds between protein monomers hold together cytoskeletal filaments. . (d) The cytoskeleton of a cell can change in response to the environment.

. 17-24 The microtubules in a cell form a structural framework that can have all the following functions except which one? . (a) holding internal organelles such as the Golgi apparatus in particular positions in the cell . (b) creating long, thin cytoplasmic extensions that protrude from one side of the cell . (c) strengthening the plasma membrane . (d) moving materials from one place to another inside a cell

. 17-35 Which of the following statements is correct? Kinesins and dyneins ____________________. . (a) have tails that bind to the filaments. . (b) move along both microtubules and actin filaments. . (c) often move in opposite directions to each other. . (d) derive their energy from GTP hydrolysis.

. 17-40 Figure Q17-40A shows how the movement of dynein causes the flagellum to bend. If instead of the normal situation, the polarity of the adjacent doublet of microtubules were to be reversed (see Figure Q17-40B), what do you predict would happen? Figure Q17-40 (a) No bending would occur. . (b) Bending would occur exactly as diagrammed in Figure Q17-40A. . (c) Bending would occur, except that the right microtubule doublet would move down relative to the left one. . (d) The two microtubule doublets would slide away from each other.

. 17-52 Figure Q17-52 shows the leading edge of a lamellipodium. Which of the following statements is false? Figure Q17-52 . (a) Nucleation of new filaments near the leading edge pushes the plasma membrane forward. . (b) ARP proteins nucleate the branched actin filaments in the lamellipodium. . (c) Capping proteins bind to the minus end of actin filaments. . (d) There is more ATP-bound actin at the leading edge than in the actin filaments away from the leading edge.

. 17-53 You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Which of the following statements is most likely to be true? . (a) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more unbranched actin filaments than normal cells. . (b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells. . (c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells. . (d) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells.

. 17-56 Which of the following structures shorten during muscle contraction? . (a) myosin filaments . (b) flagella . (c) sarcomeres . (d) actin filaments

. 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.

. 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.

. 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.

. 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.

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

. 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.

. 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.

. 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

. 19-16 There are organisms that go through meiosis but do not undergo recombination when forming haploid gametes. Which of the following statements correctly describes the gametes produced by such an organism. (Assume that these organisms are diploid, that each of the two homologous chromosomes are genetically distinct as typically found in the wild, and that these organisms have more than one chromosome.) . (a) All gametes formed during a single meiosis will be identical. . (b) Due to the random assortment of homologs, each of the gametes formed during a single meiosis will be different. . (c) This organism could potentially produce 2n genetically distinct gametes, where n is its haploid number of chromosomes. . (d) The fusion of any two gametes produced by such an organism that does not undergo recombination during meiosis will create a cell that is genetically identical to that individual.

. 19-19 In the absence of recombination, how many genetically different types of gamete can an organism with five homologous chromosome pairs produce? . (a) 5 . (b) 10 . (c) 32 . (d) 64

. 19-24 You examine a worm that has two genders: males that produce sperm and hermaphrodites that produce both sperm and eggs. The diploid adult has four homologous pairs of chromosomes that undergo very little recombination. Given a choice, the hermaphrodites prefer to mate with males, but just to annoy the worm, you pluck a hermaphrodite out of the wild and fertilize its eggs with its own sperm. Assuming that all the resulting offspring are viable, what fraction do you expect to be genetically identical to the parent worm? Assume that each chromosome in the original hermaphrodite is genetically distinct from its homolog. . (a) all . (b) none . (c) 1/16 . (d) 1/256

. 19-32 Which of the following would not lead to aneuploidy during meiosis? . (a) sister chromatids segregating inappropriately . (b) non-sister chromatids segregating inappropriately (c) a reciprocal rearrangement of parts between nonhomologous chromosomes (for example, the left arm of Chromosome 2 exchanging places with the right arm of Chromosome 3) (d) an extra set of chromosomes produced during S phase (for example, if paternal Chromosome 3 were replicated twice)

. 19-4 Somatic cells ___________________________. . (a) are not necessary for sexual reproduction in all eukaryotic organisms. . (b) are used to produce germ-line cells when organisms reach sexual maturity . (c) leave no progeny. . (d) do not contain sex chromosomes.

. 19-60 The single-nucleotide polymorphisms found in the human population __________________. . (a) are important for genetic mapping because they represent mutations in genes important for human disease. . (b) are rarely found among blood relatives. . (c) can be linked into haplotype blocks. . (d) arose mainly during the past 10,000 years.

. 19-62 Finding co-inheritance of a SNP variant and a disease tells scientists that ____________________. . (a) everybody who carries this SNP will get the disease. . (b) sequences within the SNP cause the disease. . (c) a gene important for causing the disease is linked to the SNP. . (d) SNPs on other chromosomes will not be co-inherited with the disease.

. 19-8 Which of the following does not describe a situation of asexual reproduction? . (a) A bacterium multiplying by simple cell division. . (b) Using a part of a plant to create a new independent plant. . (c) Using in vitro fertilization to combine a sperm and an egg to create an embryo. . (d) The parthenogenetic development of eggs produced by some species of lizards.

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.

19-41 Which of the following statements about the round-seeded pea plants obtained in the F2 generation is false? (See Figure Q19-38.) . (a) These plants are phenotypically identical for seed shape. . (b) Two-thirds of these plants are expected to be heterozygous for the seed- shape allele. . (c) We expect 25% of these plants to be homozygous for the seed-shape allele. . (d) If these plants were crossed to wrinkle-seeded plants, some of these plants would produce only round-seeded plants.

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

changes in cell secretion, changes in protein phosphorylation, changes in membrane potential

. 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.

. 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.

. 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.

. 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

. 17-13 Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties is not true of these types of intermediate filaments? . (a) They strengthen cells against mechanical stress. . (b) Dimers associate by noncovalent bonding to form a tetramer. . (c) They are found in the cytoplasm. . (d) Phosphorylation causes disassembly during every mitotic cycle.

. 17-16 You are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly purified nuclear lamina subunits to which you will add back purified cellular components to drive nuclear lamina assembly. Before you start doing experiments, your instructor suggests that you consider what type of conditions would be most amenable to the assembly of the nuclear lamina from its individual subunits in vitro. Which of the following conditions do you predict would be most likely to enhance the assembly of the nuclear lamina? . (a) addition of phosphatase inhibitors . (b) addition of ATP . (c) addition of a concentrated salt solution that is 10 times the concentration normally found in the nucleoplasm . (d) addition of protein kinase inhibitors

. 17-19 Which of the following statements about the structure of microtubules is false? . (a) Microtubules are built from protofilaments that come together to make a hollow structure. . (b) The two ends of a protofilament are chemically distinct, with α-tubulin exposed at one end and β-tubulin exposed at the other end. . (c) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity. . (d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

. 17-23 The hydrolysis of GTP to GDP carried out by tubulin molecules ________________. . (a) provides the energy needed for tubulin to polymerize. . (b) occurs because the pool of free GDP has run out. . (c) tips the balance in favor of microtubule assembly. . (d) allows the behavior of microtubules called dynamic instability.

. 17-28 Which of the following statements regarding dynamic instability is false? . (a) Each microtubule filament grows and shrinks independently of its neighbors. . (b) The GTP cap helps protect a growing microtubule from depolymerization. . (c) GTP hydrolysis by the tubulin dimer promotes microtubule shrinking. (d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.

. 17-33 Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure Q17-33. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be false? Figure Q17-33 . (a) The gray cargo is attached to dynein. . (b) The black cargo and the gray cargo require ATP hydrolysis for their motion. . (c) The black cargo moving toward the axon terminal contains a domain that specifically interacts with the tail domain of a particular kind of motor. . (d) The black cargo and the gray cargo are moving along microtubules of opposite polarity.

. 17-4 Which of the following statements about the cytoskeleton is true? . (a) All eukaryotic cells have actin, microtubules, and intermediate filaments in their cytoplasm. . (b) The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell. . (c) The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another. . (d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.

. 17-42 Which of the following statements about actin is false? . (a) ATP hydrolysis decreases actin filament stability. . (b) Actin at the cell cortex helps govern the shape of the plasma membrane. . (c) Actin filaments are nucleated at the side of existing actin filaments in lamellipodia. . (d) The dynamic instability of actin filaments is important for cell movement.

. 17-45 For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______. . (a) stabilizing the filaments once they are formed. . (b) increasing the rate at which subunits are added to the filaments. . (c) promoting nucleation of filaments. . (d) decreasing the binding strength between subunits on filaments.

. 17-50 Cell movement involves the coordination of many events in the cell. Which of the following phenomena is not required for cell motility? . (a) Myosin-mediated contraction at the rear of the moving cell. . (b) Integrin association with the extracellular environment. . (c) Nucleation of new actin filaments. . (d) Release of Ca2+ from the sarcoplasmic reticulum.

. 17-6 Which of the statements below about intermediate filaments is false? . (a) They can stay intact in cells treated with concentrated salt solutions. . (b) They can be found in the cytoplasm and the nucleus. . (c) They can be anchored to the plasma membrane at a cell-cell junction. . (d) Each filament is about 10 μm in diameter.

. 17-63 Consider the in vitro motility assay using purified kinesin and purified polymerized microtubules shown in Figure Q17-63. The three panels are images taken at 1-second intervals. In this figure, three microtubules have been numbered to make it easy to identify them. Which of the following statements about this assay is false? Figure Q17-63 . (a) Kinesin molecules are attached by their tails to a glass slide. . (b) The microtubules used in this assay must be polymerized using conditions that stabilize tubule formation or else they would undergo dynamic instability. . (c) ATP must be added for this assay to work. . (d) Addition of the nonhydrolyzable ATP analog (AMP-PNP) would cause the microtubules to move faster.

. 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.

. 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.

. 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.

. 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.

. 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.

. 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.

. 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.

. 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

. 18-48 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.

. 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

. 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.

. 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

. 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.

. 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.

. 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.

. 19-1 Organisms that reproduce sexually ________________________. . (a) must be haploid, unlike organisms that reproduce asexually. . (b) can reproduce only with a partner that carries the same alleles. . (c) create zygotes that are genetically identical to each other. . (d) undergo a sexual reproductive cycle that involves an alternation of haploid cells with the generation of diploid cells.

. 19-15 Imagine meiosis in a diploid organism that only has a single chromosome. Like most diploid organisms, it received one copy of this chromosome from each of its parents and the two homologs are genetically distinct. If only a single homologous recombination event occurs during meiosis, which of the following choices below correctly describes the four gametes formed. . (a) None of the gametes will contain chromosomes identical to the chromosomes found in the original diploid cell. . (b) All four of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell. . (c) Three of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while one of the gametes will have chromosomes that are different. (d) Two of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while two of the gametes will have chromosomes that are different.

. 19-20 Which of the following statements most correctly describes meiosis? . (a) Meiosis involves two rounds of DNA replication followed by a single cell division. . (b) Meiosis involves a single round of DNA replication followed by four successive cell divisions. . (c) Meiosis involves four rounds of DNA replication followed by two successive cell divisions. . (d) Meiosis involves a single round of DNA replication followed by two successive cell divisions.

. 19-33 A single nondisjunction event during meiosis ___________________. . (a) will block recombination. . (b) will occur only during meiosis II. . (c) cannot occur with sex chromosomes. . (d) will involve the production of two normal gametes if it occurs during meiosis II.

. 19-43 Which of the following reasons was essential for Mendel to disprove the theory of blended inheritance? . (a) The traits that Mendel examined all involved genes that did not display linkage. . (b) The traits that Mendel examined all involved the reproductive structures of the pea plant. . (c) Mendel pioneered techniques permitting the fusion of male and female gametes from the same plant to produce a zygote. . (d) The traits that Mendel examined involved an allele that was dominant and an allele that was recessive.

. 19-61 Which of the following statements about genome-wide association studies (GWAS) is false? . (a) GWAS use SNPs to compare populations of people with disease and people without disease to look for SNPs more likely to be present in those with disease. . (b) GWAS can be used even if more than one gene can cause the disease of interest. . (c) Sometimes GWAS will identify SNPs that are associated with a disease but these SNPs do not affect the gene product of the gene that causes the disease. . (d) Studies using GWAS only examine SNPs that occur very rarely (<0.001%) in the population, as those SNPs are most likely to cause disease.

. 19-7 During sexual reproduction, novel mixtures of alleles are generated. This is because ______. . (a) in all diploid species, two alleles exist for every gene. . (b) a diploid individual has two different alleles for every gene. . (c) every gamete produced by a diploid individual has several different alleles of a single gene. . (d) during meiosis, the segregation of homologs is random such that different gametes end up with different alleles of each gene.

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.

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.

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.

17-55 Your friend works in a biotech company that has just discovered a drug that seems to promote lamellipodia formation in cells. Which of the following molecules is unlikely to be involved in the pathway that this drug affects? . (a) Rac . (b) ARP . (c) actin . (d) myosin

19-37 Which of the following statements about Mendel's experiments is false? . (a) The pea plants could undergo both cross-fertilization and self-fertilization. . (b) The true-breeding strains were homozygous for the traits that Mendel examined. . (c) The egg can carry either the allele from the maternal or the paternal chromosome. . (d) All traits that Mendel studied were recessive.

19-53 Loss-of-function mutations ________________________. . (a) cause the production of proteins that are active in inappropriate circumstances. . (b) will usually show a phenotype when heterozygous. . (c) are only present in a population at barely detectable levels. . (d) are usually recessive.

. 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

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 __________________. 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. The regulatory component of MPF, called __________________, has a __________________ effect on MPF activity and plays a part in regulating interactions with its __________________s. The components of MPF are evolutionarily __________________ from yeast to humans, so that the corresponding human genes are __________________ to function in yeast.

egg, G2, short, synchronously, maturation promoting factor, oscillate, Cdk, cyclin, stimulatory, substrates, conserved, able

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

endocrine, contact-dependent, paracrine, neuronal, receptor

. 19-65 You decide to carry out genetic association studies and identify a SNP variant that is found significantly more often in individuals who have schizophrenia than in those who are not affected. This SNP is found within an intron of the SZP gene. A. Can you deduce that an abnormality of the SZP gene is a cause of increased risk of schizophrenia? B. Can you say whether the SNP variant itself is a cause?

no, no

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

endocrine, contact-dependent, paracrine, neuronal, receptor

To reproduce sexually, an organism must create haploid __________________ cells, or __________________, from diploid cells via a specialized cell division called __________________. During mating, the father's haploid cells, called __________________ in animals, fuse with the mother's haploid cells, called __________________. Cell fusion produces a diploid cell called a __________________, which undergoes many rounds of cell division to create the entire body of the new individual. The cells produced from the initial fusion event include __________________ cells that form most of the tissues of the body as well as the __________________-line cells that give rise to the next generation of progeny.

germ, gametes, meiosis, sperm, eggs, zygote, somatic, germ

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

head, tail, coil-coiled, two, eight, ten, globular

. 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. 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]. 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.

increase, prophase, plus, increase, larger, shorter, unchanged, shrinkage, reduced, increased, replicated chromosomes

16-20 Name the three main classes of cell-surface receptor.

ion-channel-coupled receptors, G-protein-coupled receptors, enzyme-coupled receptors

. 16-16 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? ;Although succinylcholine can bind to the acetylcholine receptor, it does not activate the receptor and therefore does not cause the muscle cell to contract. Instead, succinylcholine blocks the ability of acetylcholine to bind to the receptor and thereby prevents acetylcholine from stimulating muscle contraction.

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

keratin, desmosomes, vimentin, neurofilaments, plectin, lamin

Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely __________________ concentration of free Ca2+ in the cytosol, compared with its concentration in the __________________ space and in the __________________, creating a steep electrochemical gradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as __________________, which also binds diacylglycerol, and __________________, which activates CaM-kinases.

low, extracellular, endoplasmic reticulum, protein kinase C, calmodulin

. 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

metaphase, prometaphase, pro metaphase, cytokinesis, prophase, telophase, prophase, anaphase

Gregor Mendel studied pea plants and developed some very important ideas about how genes are inherited. These studies used plant strains that were true breeding and always produced progeny that had the same __________________ as the parent. These strains were true breeding because they were __________________ for the gene important for a specific trait. In other words, for these true-breeding strains, both chromosomes in the diploid pea plant carried the same __________________ of the gene. Mendel started out examining the inheritance of a single trait at a time, and then moved on to examining two traits at once in a __________________ cross. His studies examining the inheritance of two traits in one cross allowed him to discover what is now known as Mendel's law of __________________ assortment. Geneticists can study the inheritance of specific traits in humans by analyzing a __________________, which shows the phenotypes of different family members over several generations for a particular trait.

phenotype, homozygous, allele, dihybrid, independent, pedigree

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. 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. 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.

proliferation, receptor, mitogens, G0, G1, growth factors, survival factors, apoptosis, Bcl2, myostatin

An extracellular signal molecule can act to change a cell's behavior by acting through cell-surface __________________ that control intracellular signaling proteins. These intracellular signaling proteins ultimately change the activity of __________________ proteins that bring about cell responses. Intracellular signaling proteins can __________________ the signal received to evoke a strong response from just a few extracellular signal molecules. A cell that receives more than one extracellular signal at the same time can __________________ this information using intracellular signaling proteins. __________________ proteins can act as molecular switches, letting a cell know that a signal has been received. Enzymes that phosphorylate proteins, termed ___________, can also serve as molecular switches; the actions of these enzymes are countered by the activity of __________________.

receptors, effector, amplify, integrate, GTP-binding, protein kinases, protein phosphates

G-protein-coupled receptors (GPCRs) all have a similar structure with __________________ transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of __________________ subunits, becomes activated. __________________ of the G-protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the α subunit is bound to __________________, which is exchanged for __________________ on stimulation. The intrinsic __________________ activity of the α subunit is important for inactivating the G protein. __________________ inhibits this activity of the α subunit, thereby keeping the subunit in an active state.

seven, three, two, GDP, GTP, GTPase, Cholera toxin

. 19-18 For each of the following sentences, choose one of the options enclosed in square brackets to make a correct statement. Starting with a single diploid cell, mitosis produces [two/four] [identical/different] [haploid/diploid] cells, whereas meiosis yields [two/four] [identical/different] [haploid/diploid] cells. This is accomplished in meiosis because a single round of chromosome [replication/segregation] is followed by two sequential rounds of [replication/segregation]. Mitosis is more like meiosis [I/II] than meiosis [I/II]. In meiosis I, the kinetochores on sister chromatids behave [independently/coordinately] and thus attach to microtubules from the [same/opposite] spindle. The cohesin-mediated glue between [chromatids/homologs] is regulated differently near the centromeres than along the chromosome arms. Cohesion is lost first at the [centromeres/arms] to allow segregation of [chromatids/homologs] and is lost later at the [centromeres/arms] to trigger segregation of [chromatids/homologs].

two identical diploid, four different haploid, replication, segregation, II, I, coordinately, same, chromatids, arms, homologs, centromeres, chromatids

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