Which of the following does not occur during M phase in animal cells?

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

Answer: 

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?

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.

Answer: 

How does S-Cdk help guarantee that replication occurs only once during each cell cycle?

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.

Answer: 

Which of the following statements is false?

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.

Answer: 

Cells in the G0 state ________________.

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.

Answer: 

The G1 DNA damage checkpoint ________________.

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.

Answer: 

The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______.

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.

Answer: 

Mitogens are _____.

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.

Answer: 

Which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution?

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.

Answer: 

Which of the following statements is false?

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.

Answer: 

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?

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.

Answer: 

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?

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

Answer: 

The concentration of mitotic cyclin (M cyclin) ________________.

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.

Answer: 

Levels of Cdk activity change during the cell cycle, in part because ________________.

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.

Answer: 

Progression through the cell cycle requires a cyclin to bind to a Cdk because _________.

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.

Answer: 

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?

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

Answer: 

Which of the following statements about the cell cycle is false?

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.

Answer: 

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated?

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

Answer: 

Which of the following events does not usually occur during interphase?

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.

Answer: 

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.Which of the following would not explain the results with the mutant?

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.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

Answer: 

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

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.

Answer: 

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?

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?

(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

Answer: 

Which of the following statements about skeletal muscle contraction is false?

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.

Answer: 

Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction?

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

Answer: 

Figure Q17-57 shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled.Which of the following statements is true about muscle contraction?

Figure Q17-57 shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled.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.

Answer: 

Which of the following structures shorten during muscle contraction?

Which of the following structures shorten during muscle contraction?

(a) myosin filaments
(b) flagella
(c) sarcomeres
(d) actin filaments

Answer: 

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?

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

Answer: 

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?

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.

Answer: 

Figure Q17-52 shows the leading edge of a lamellipodium. Which of the following statements is false?

Figure Q17-52 shows the leading edge of a lamellipodium. Which of the following statements is false?

(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.

Answer: 

Cell movement involves the coordination of many events in the cell. Which of the following phenomena is not required for cell motility?

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.

Answer: 

Which of the following statements is false?

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.

Answer: 

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?

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.

Answer: 

For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______.

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.

Answer: 

Which of the following statements about actin is false?

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.

Answer: 

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 Q17-40A 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?

(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.

Answer: 

Which of the following items is not important for flagellar movement?

Which of the following items is not important for flagellar movement?

(a) sarcoplasmic reticulum
(b) ATP
(c) dynein
(d) microtubules

Answer: 

Which of the following statements is correct? Kinesins and dyneins _______.

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.

Answer: 

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?

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?

(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.

Answer: 

Which of the following statements about organellar movement in the cell is false?

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.

Answer: 

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. 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?

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.
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.

Answer: 

Which of the situations below will enhance microtubule shrinkage?

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 ?-tubulin

Answer: 

Which of the following statements regarding dynamic instability is false?

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.

Answer: 

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 ________________.

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.

Answer: 

The microtubules in a cell form a structural framework that can have all the following functions except which one?

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

Answer: 

The hydrolysis of GTP to GDP carried out by tubulin molecules ________________.

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.

Answer: 

Which of the following statements about microtubules is true?

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.

Answer: 

Which of the following statements about the function of the centrosome is false?

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 ?-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.

Answer: 

Which of the following statements about the structure of microtubules is false?

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 a-tubulin exposed at one end and ß-tubulin exposed at the other end.
(c) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity.
(d) a-Tubulin and ß-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

Answer: 

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?

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

Answer: 

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)?

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.

Answer: 

Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties is not true of these types of intermediate filaments?

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.

Answer: 

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 a-helical region is twice as long as that of a normal intermediate filament by duplicating the normal a-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFad. If you were to assemble intermediate filaments using IFad as the subunit, which of the following predictions describes the most likely outcome?

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 a-helical region is twice as long as that of a normal intermediate filament by duplicating the normal a-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFad. If you were to assemble intermediate filaments using IFad as the subunit, which of the following predictions describes the most likely outcome?

(a) Filaments assembled using IFad will interact with different cytoskeletal components.
(b) Filaments assembled using IFad will form dimers that are twice as long as dimers assembled from normal intermediate filaments.
(c) Sixteen tetramers assembled from IFad will be needed for a ropelike structure to form.
(d) Dimers of IFad will form by interactions with the N-terminal globular head and the C-terminal globular tail.

Answer: 

Intermediate filaments help protect animal cells from mechanical stress because ____________.

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.

Answer: 

All intermediate filaments are of similar diameter because ____________.

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.

Answer: 

Which of the statements below about intermediate filaments is false?

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.

Answer: 

Which of the following statements about the cytoskeleton is true?

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.

Answer: 

Which of the following statements about the cytoskeleton is false?

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.

Answer: 

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 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?

(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

Answer: 

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?

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.

Answer: 

Figure Q16-61 shows that intracellular signaling pathways can be highly interconnected.From the information in Figure Q16-61, which of the following statements is incorrect?

Figure Q16-61 shows that intracellular signaling pathways can be highly interconnected.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.

Answer: 

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. Which of the following statements is inconsistent with your data?

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. 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.

Answer: