Chapter 17

1.

1 point

During muscle contraction, the myosin and actin filaments do not change in length:

False

True

2.

1 point

Which of the following statements about the cytoskeleton is false?

The bacterial cytoskeleton is important for cell division and DNA segregation.

Protein monomers that are held together with covalent bonds form cytoskeletal filaments.

The cytoskeleton of a cell can change in response to the environment.

The cytoskeleton is made up of three types of filament.

3.

1 point

Intermediate filaments are:

tubelike structures.

ropelike structures.

springlike structures.

meshlike structures.

4.

1 point

In eukaryotic cells, the cell cortex is made of:

a network of microtubules.

a network of actin filaments.

a network of intermediate filaments.

5.

1 point

Which of the following statements about actin is false?

Actin filaments are nucleated at the side of existing actin filaments in lamellipodia.

ATP hydrolysis decreases actin filament stability.

The dynamic instability of actin filaments is important for cell movement.

Actin at the cell cortex helps govern the shape of the plasma membrane.

6.

1 point

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

Motor proteins involved in organellar movement use ATP hydrolysis for energy.

Organelles are attached to the tail domain of motor proteins.

Only the microtubule cytoskeleton is involved in organellar movement.

Organelles undergo saltatory movement in the cell.

7.

1 point

Inside a muscle fiber, what triggers sarcomeres to contract?

A sudden rise in intracellular Na+

An increased availability of ATP

A sudden rise in intracellular Ca2+

Polarization of the muscle fiber’s membrane

8.

1 point

Myosin-I is present in:

nerve cells only.

all types of cells.

epithelial cells only.

muscle cells only.

9.

1 point

Which of the following statements regarding dynamic instability is false?

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

GTP hydrolysis by the tubulin dimer promotes microtubule shrinking.

Each microtubule filament grows and shrinks independently of its neighbors

The GTP cap helps protect a growing microtubule from depolymerization.

10.

1 point

The hydrolysis of bound ATP to ADP in an actin filament _____ the strength of binding between monomers in the filament.

has no effect on

increases

decreases

11.

1 point

Movement of materials in polarized cells by free diffusion is faster and more efficient than that guided by microtubules.

True

False

12.

1 point

Cell crawling depends on:

actin polymerization

microtubule assembly

hydrolysis of ADP by motor proteins

intermediate filaments.

13.

1 point

Which of the following cytoskeletal structures provides tracks for long-distance intracellular transport?

Actin filaments

Intermediate filaments

Microtubules

14.

1 point

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 below is unlikely to be involved in the pathway that this drug affects?

actin

Rac

myosin

ARP

15.

1 point

Keratins are NOT found in:

the tongue.

feathers.

hair.

bones.

16.

1 point

Dynamic instability is:

the ability of a microtubule to switch polarity back and forth between a positive and negative charge

the ability of a microtubule to shrink rapidly during mitosis.

the ability of a microtubule to switch back and forth between polymerization and depolymerization.

the ability of a microtubule to grow rapidly during meiosis.

17.

1 point

Akt (a.k.a. PKB) promotes the survival of many cells. It is activated by an intracellular signaling pathway that is triggered by an RTK that activates PI 3-kinase. Which of the following statements is false?

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

In the presence of a survival signal, Akt localizes to the plasma membrane by binding to PIP3.

In the absence of survival signal, Bad is phosphorylated.

In the absence of survival signal, Bad inhibits the cell death inhibitor protein Bcl2.

18.

1 point

Which of the following types of intermediate filaments are found in all animal cells?

Vimentin and vimentin-related filaments

Keratins

Nuclear lamins

Neurofilaments

19.

1 point

Which of the following statements is false?

ARPs can promote the formation of branched actin filaments.

Actin filaments are usually excluded from the cell cortex.

Integrins are transmembrane proteins that can bind to the extracellular matrix.

Cytochalasins prevent actin polymerization.

20.

1 point

Which end of a microtubule is embedded in the centrosome?

The plus end

The minus end

21.

1 point

What is the name of the thin sheetlike structures that a fibroblast regularly extends during cell crawling?

Filopodia

Pseudopods

Lamellipodia

Phagosomes

22.

1 point

Which does NOT contain myosin?

The contractile ring that carries out cytokinesis

A muscle cell sarcomere

The filopodium at the leading edge of a crawling cell

23.

1 point

The long fibers of a skeletal muscle are:

one large cell with many nuclei.

one large cell with a single nucleus.

many cells organized end-to-end.

24.

1 point

A key group of proteins that regulate the actin cytoskeleton is:

the Rab protein family.

the Rho protein family.

the Ras protein family.

the Ran protein family.

25.

1 point

Which of the following statements about microtubules is true?

Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell.

The centromere nucleates the microtubules of the mitotic spindle.

ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.

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

26.

1 point

Which is the toughest and most durable of the three types of cytoskeletal filaments?

Actin filaments

Microtubules

Intermediate filaments

27.

1 point

The end of a growing microtubule is rich in which type of tubulin molecule?

GTP-associated tubulin molecules

GDP-associated tubulin molecules

28.

1 point

The nuclear lamina disassembles and re-forms at each cell division.

False

True

29.

1 point

Microtubules are:

rope-like strands.

mesh-like networks.

hollow tubes.

interlocking chains.

30.

1 point

Myosins are motor proteins that use the energy of ATP hydrolysis to move along actin filaments.

A. False

B. True

31.

1 point

In eukaryotic flagellum, the bending of microtubules is driven by:

the basal body.

the motor protein ciliary dynein.

actin and myosin.

the fluid that surrounds the flagellum.

32.

1 point

Which of the following describes the structure of an actin filament?

It is a double helix made of actin molecules.

It is a structure with a long tail and two globular heads.

It is a hollow cylinder made up of actin molecules.

33.

1 point

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

occurs because the pool of free GDP has run out

allows the behavior of microtubules called dynamic instability

provides the energy needed for tubulin to polymerize

tips the balance in favor of microtubule assembly

34.

1 point

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

a mutation in tropomyosin that decreases its affinity for the actin filament

addition of a drug that blocks Ca2+ binding to troponin

an increase in the amount of ATP in the cell

partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero

35.

1 point

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

Dimers associate by noncovalent bonding to form a tetramer.

They are found in the cytoplasm.

They strengthen cells against mechanical stress.

Phosphorylation causes disassembly during every mitotic cycle.

36.

1 point

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?

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.

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.

Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells.

Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells.

37.

1 point

As a cell grows, which microtubule-associated protein pulls the ER membrane outward, stretching it like a net?

Kinesin

Actin

Cohesin

Dynein

38.

1 point

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

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.

When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane.

During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.

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.

39.

1 point

Which of the following is the main function of intermediate filaments?

To provide tracks for guiding intracellular transport

To enable cells to withstand the mechanical stress that occurs when cells are stretched

To enable cells to crawl