Question 1

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

Accepted Answer

The release of Ca²⁺ from the sarcoplasmic reticulum is a process specific to muscle cells and is not required for general cell motility. The other options are all important for cell movement: myosin-mediated contraction helps to move the cell forward, integrin association with the extracellular environment facilitates adhesion and traction, and nucleation of new actin filaments is necessary for the formation of the leading edge of the cell.

Question 2

Figure 17-24A 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 17-24B), what do you predict would happen? (A)

(B)

Figure 17-24

Accepted Answer

The answer of Figure 17-24A shows how the movement of...

Question 3

Which of the following statements is FALSE?

Accepted Answer

Actin filaments are not usually excluded from the cell cortex, in fact, they are a major component of the cell cortex in many cell types. The cell cortex is the region just beneath the plasma membrane, which contains a dense meshwork of actin filaments and associated proteins that provide mechanical support and help to maintain cell shape.

Question 4

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?

Accepted Answer

Rac activation leads to the formation of lamellipodia, which are characterized by branched actin filaments. Therefore, cells carrying a Rac mutation that promotes the always-bound-to-GTP state (i.e. active) will polymerize more branched actin filaments than normal cells.

Question 5

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

Accepted Answer

The sarcoplasmic reticulum is involved in muscle contraction, not in flagellar movement, which relies on structures and mechanisms like ATP for energy, dynein for motor activity, and microtubules for structural support.

Question 6

Identify the cytoskeletal structures (black lines) depicted in the epithelial cells shown in Figure 17-1. (A)

(B)

(C)

Figure 17-1

Accepted Answer

The answer of Identify the cytoskeletal structures (black lines) depicted...

Question 7

Kinesins and dyneins

Accepted Answer

Kinesins and dyneins are motor proteins that move along microtubules, not actin filaments, and they often move in opposite directions: kinesins typically move toward the plus end, while dyneins move toward the minus end. They derive their energy from ATP hydrolysis, not GTP.

Question 8

Which of the following statements about the movement of materials in a nerve axon is TRUE?

Accepted Answer

Microtubules in axons are oriented with their minus ends toward the cell body and plus ends toward the axon terminal, facilitating directional transport.

Question 9

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

Accepted Answer

Ca2+ binding to troponin is necessary for the contraction of skeletal muscle. If a drug binds to troponin and prevents Ca2+ from binding, it will decrease the likelihood of muscle contraction. All of the other choices listed would increase the likelihood of muscle contraction.

Question 10

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?

Accepted Answer

Depolymerization of microtubules can initiate at either the plus or minus ends, but for actin filaments, depolymerization predominantly occurs at the minus end. This makes choice B incorrect as it does not accurately describe a similarity between the polymerization mechanisms of actin and microtubules.

Question 11

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

Accepted Answer

The answer of Rank the following cytoskeletal filaments from smallest...

Question 12

Figure 17-31 shows the leading edge of a lamellipodium.Which of the following statements is FALSE?  Figure 17-31

Accepted Answer

Capping proteins bind to the plus end of actin filaments, not the minus end.

Question 13

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 directly involved in the pathway that this drug affects?

Accepted Answer

Myosin is not directly involved in the lamellipodia formation pathway. Rather, myosin functions in the contraction of actin filaments to promote cellular movement.

Question 14

Figure 17-38 shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled.  Figure 17-38
Which of the following statements is TRUE about muscle contraction?

Accepted Answer

According to the sliding filament theory of muscle contraction, the overlapping actin and myosin filaments slide past each other, causing the sarcomere (region between two Z lines) to shorten. Therefore, as the muscle fiber contracts, point B (located at the center of the sarcomere) will move closer to point C (located at the Z line), while point A (located at the opposite end of the sarcomere) will also move closer to point B. Region D (the H zone, located in the center of the A band) will become smaller as the actin filaments slide inward, but region E (the I band, located between two adjacent A bands) will not necessarily shrink in size.

Question 15

Which of the following structures shorten during muscle contraction?

Accepted Answer

The basic contractile unit of a muscle is the sarcomere. During muscle contraction, the sarcomeres within the muscle fibers shorten, causing the muscle to contract. The myosin and actin filaments within the sarcomeres slide past each other, causing the sarcomeres to shorten. Flagella are not found in muscle cells, so they are not involved in muscle contraction.

Question 16

Which of the following statements about actin is FALSE?

Accepted Answer

Actin filaments do not exhibit dynamic instability; instead, they undergo treadmilling, which is important for cell movement. Dynamic instability is a characteristic of microtubules, not actin filaments.

Question 17

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

Accepted Answer

The influx of Ca2+ into the sarcoplasmic reticulum actually triggers muscle relaxation, not contraction. The correct sequence of events is as follows: when a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane, leading to an influx of Na+ into the cell. This depolarizes the membrane and triggers the opening of Ca2+ channels in the sarcoplasmic reticulum, causing a release of Ca2+ into the cytoplasm. The Ca2+ binds to troponin, leading to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. The myosin heads then perform a power stroke, pulling the actin filament towards the center of the sarcomere and causing muscle contraction. Lastly, during muscle contraction, the Z discs move closer together as the actin filaments slide past the myosin filaments.

Question 18

Consider the in vitro motility assay using purified kinesin and purified polymerized microtubules shown in Figure 17-37.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 17-37

Accepted Answer

Addition of the nonhydrolyzable ATP analog (AMP-PNP) would not cause the microtubules to move faster. In fact, it would cause the microtubules to not move at all, as AMP-PNP cannot be hydrolyzed by kinesin to provide energy for movement.

Question 19

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?

Accepted Answer

Actin filament dynamics are influenced by the hydrolysis of ATP to ADP. Monomers with nonhydrolyzable ATP would not undergo this transition, potentially stabilizing their incorporation into filaments and promoting longer filament growth, as they are less likely to depolymerize.

Question 20

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

Accepted Answer

Nucleotide hydrolysis decreases the binding strength between subunits, which is crucial for the dynamic instability of microtubules and the treadmilling of actin filaments, allowing for rapid reorganization of the cytoskeleton.

Quiz 17: Cytoskeleton

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

Figure 17-24A 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 17-24B) , what do you predict would happen? (A) (B) Figure 17-24

Which of the following statements is FALSE?

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?

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

Identify the cytoskeletal structures (black lines) depicted in the epithelial cells shown in Figure 17-1. (A) (B) (C) Figure 17-1

Kinesins and dyneins

Which of the following statements about the movement of materials in a nerve axon is TRUE?

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

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?

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

Figure 17-31 shows the leading edge of a lamellipodium.Which of the following statements is FALSE? Figure 17-31

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 directly involved in the pathway that this drug affects?

Figure 17-38 shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled. Figure 17-38 Which of the following statements is TRUE about muscle contraction?

Which of the following structures shorten during muscle contraction?

Which of the following statements about actin is FALSE?

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

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?

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

Quiz 17: Cytoskeleton

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

Figure 17-24A 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 17-24B) , what do you predict would happen? (A) (B) Figure 17-24

Which of the following statements is FALSE?

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?

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

Identify the cytoskeletal structures (black lines) depicted in the epithelial cells shown in Figure 17-1. (A) (B) (C) Figure 17-1

Kinesins and dyneins

Which of the following statements about the movement of materials in a nerve axon is TRUE?

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

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?

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

Figure 17-31 shows the leading edge of a lamellipodium.Which of the following statements is FALSE? Figure 17-31

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 directly involved in the pathway that this drug affects?

Figure 17-38 shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled. Figure 17-38 Which of the following statements is TRUE about muscle contraction?

Which of the following structures shorten during muscle contraction?

Which of the following statements about actin is FALSE?

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

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?

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

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