Question 1

What would occur if CapZ was inhibited in cells?

Accepted Answer

A) increased organization of actin in stereocilia due to stabilized actin dynamics 
B) increased rates of polymerization due to reduced availability for ADP-G-actin 
C) increased steady-state treadmilling of F-actin 
D) faster movement of cells toward a chemical signal 
A) increased organization of actin in stereocilia due to stabilized actin dynamics 
B) increased rates of polymerization due to reduced availability for ADP-G-actin 
C) increased steady-state treadmilling of F-actin 
D) faster movement of cells toward a chemical signal C

Question 2

Which of the following proteins is involved in formation of actin bundles in microvilli by providing crosslinks between actin filaments?

Accepted Answer

A) α actinin 
B) cofilin 
C) fimbrin 
D) profilin 
A) α actinin 
B) cofilin 
C) fimbrin 
D) profilin C

Question 3

Like Listeria,other bacterial pathogens have also evolved to take advantage of actin-based cell motility systems in their hosts.For example,some pathogenic strains of E.coli make a cytotoxic factor (CNF1)that converts a specific glutamine residue on RhoGTPases to glutamate.This change blocks both the intrinsic and GAP-stimulated GTP hydrolysis activity of the Rho protein.Predict the effects of CNF1 on human epithelial cells in culture.

Accepted Answer

If GTP hydrolysis were blocked,Rho would remain constitutively active.Similar to the effects of dominant active Rho mutants,this would result in the formation of stress fibers in the tissue culture cells.(Stress fiber formation would allow the cultured epithelial cells to spread. )
Reference for the data cited in this question: Fiorentini,C. ,et al.1997.Escherichia coli Cytotoxic Necrotizing Factor I (CNF1),a Toxin That Activates the Rho GTPase.J.Biol.

Question 4

What contractile structure is essential for cell division?

Accepted Answer

The contractile ring is a transient cont

Question 5

Listeria is a bacterial parasite that has evolved unique ways to enter animal cells and then use actin polymerization for its intracellular movement.Which of the following statements is true in regards to Listeria and actin polymerization?

Accepted Answer

A) Listeria ActA protein binds and inactivates the Arp2/3 complex. 
B) Listeria ActA binds VASP,which enhances ATP-actin assembly. 
C) Cofilin is necessary to accelerate the assembly of the (−)end of the filament. 
D) CapZ promotes the elongation of the filament. 
A) Listeria ActA protein binds and inactivates the Arp2/3 complex. 
B) Listeria ActA binds VASP,which enhances ATP-actin assembly. 
C) Cofilin is necessary to accelerate the assembly of the (−)end of the filament. 
D) CapZ promotes the elongation of the filament.

Question 6

The plasma membrane of eukaryotic cells is supported by:

Accepted Answer

A) actin filaments. 
B) microtubules. 
C) lamins. 
D) intermediate filaments. 
A) actin filaments. 
B) microtubules. 
C) lamins. 
D) intermediate filaments.

Question 7

In the budding yeast S.cerevisiae,which of the following is NOT transported into the bud by myosin V?

Accepted Answer

A) peroxisome 
B) vacuole 
C) mRNA 
D) nucleus 
A) peroxisome 
B) vacuole 
C) mRNA 
D) nucleus

Question 8

Membrane extension during cell locomotion is driven by:

Accepted Answer

A) myosin II. 
B) actin depolymerization. 
C) contraction. 
D) actin polymerization. 
A) myosin II. 
B) actin depolymerization. 
C) contraction. 
D) actin polymerization.

Question 9

What cellular components cause some actin filaments to form bundles and others to form networks?

Accepted Answer

Different actin-binding proteins (ABPs)c

Question 10

If the activity of thymosin β4 was inhibited in fibroblasts,the overall effect would be:

Accepted Answer

A) a decrease in cell locomotion because less actin would be recruited to the leading edge. 
B) an increase in cell locomotion because there would be a higher concentration of actin available. 
C) no change in cell locomotion because thymosin β4 doesn't interact with Rho,Rac,or Cdc42. 
D) none of the above 
A) a decrease in cell locomotion because less actin would be recruited to the leading edge. 
B) an increase in cell locomotion because there would be a higher concentration of actin available. 
C) no change in cell locomotion because thymosin β4 doesn't interact with Rho,Rac,or Cdc42. 
D) none of the above

Question 11

In response to a chemotactic signal,a cell forms structures to aid in locomotion.In lamellipodia,active Rac will stimulate F-actin polymerization at the leading edge via _____,whereas actin that will form stress fibers will be recruited by formin downstream of activation of this small GTPase _____.

Accepted Answer

A) Arp 2/3;Rho 
B) Arp 2/3;Cdc42 
C) WASP;Rho 
D) Rho kinase;Cdc42 
A) Arp 2/3;Rho 
B) Arp 2/3;Cdc42 
C) WASP;Rho 
D) Rho kinase;Cdc42

Question 12

What is the function of CapZ and tropomodulin in the sarcomere?

Accepted Answer

A) to center myosin thick filaments 
B) to attach actin thin filaments to the Z disk 
C) to maintain a constant actin thin filament length 
D) to make contraction sensitive to Ca²⁺ 
A) to center myosin thick filaments 
B) to attach actin thin filaments to the Z disk 
C) to maintain a constant actin thin filament length 
D) to make contraction sensitive to Ca²⁺

Question 13

At ATP-G-actin concentrations that are intermediate between the Cc for the (+)end and the Cc for the (-)end,_____ will be observed.The Cc needed for elongation at the (+)end is _____ than that at the (-)end of actin microfilaments.

Accepted Answer

A) growth;lower 
B) shrinking,higher 
C) treadmilling,lower 
D) none of the above 
A) growth;lower 
B) shrinking,higher 
C) treadmilling,lower 
D) none of the above

Question 14

The correct order of events in cell locomotion is:

Accepted Answer

A) rear focal adhesion,membrane protrusion,front focal adhesion,cell body translocation,de-adhesion. 
B) membrane protrusion,front focal adhesion,cell body translocation,de-adhesion,rear focal adhesion. 
C) front focal adhesion,cell body translocation,de-adhesion,rear focal adhesion,membrane protrusion. 
D) cell body translocation,de-adhesion,rear focal adhesion,membrane protrusion,front focal adhesion. 
A) rear focal adhesion,membrane protrusion,front focal adhesion,cell body translocation,de-adhesion. 
B) membrane protrusion,front focal adhesion,cell body translocation,de-adhesion,rear focal adhesion. 
C) front focal adhesion,cell body translocation,de-adhesion,rear focal adhesion,membrane protrusion. 
D) cell body translocation,de-adhesion,rear focal adhesion,membrane protrusion,front focal adhesion.

Question 15

Within an actin filament,each actin subunit is surrounded by _____ neighboring actin subunits.

Accepted Answer

A) one 
B) two 
C) four 
D) eight 
A) one 
B) two 
C) four 
D) eight

Question 16

Human erythrocytes depend on microfilament networks to provide strength and flexibility.Describe this network and explain how microfilaments are attached to the plasma membrane in human erythrocytes.

Accepted Answer

The microfilament network that underlies

Question 17

What actin-binding protein mediates gel-sol transitions,and how is this protein's activity regulated?

Accepted Answer

Gel-sol transitions are mediat

Question 18

All of the following statements about actin assembly are correct EXCEPT:

Accepted Answer

A) ATP-actin can assemble into filaments. 
B) actin subunits can treadmill through an actin filament. 
C) actin assembly can produce force for movement. 
D) actin (−)ends assemble more rapidly than actin (+)ends. 
A) ATP-actin can assemble into filaments. 
B) actin subunits can treadmill through an actin filament. 
C) actin assembly can produce force for movement. 
D) actin (−)ends assemble more rapidly than actin (+)ends.

Question 19

A well-coordinated mechanism involving cell-surface receptors and the actin cytoskeleton allows leukocytes to bind and engulf invading bacteria.Briefly describe how bacteria are phagocytosed.

Accepted Answer

In a process termed opsonization,antibod

Question 20

The elastic Brownian ratchet model has been proposed to explain:

Accepted Answer

A) membrane extension. 
B) focal adhesion formation. 
C) cell-body translocation. 
D) gel-sol transitions. 
A) membrane extension. 
B) focal adhesion formation. 
C) cell-body translocation. 
D) gel-sol transitions.

Exam 16: Cell Organization and Movement I: Microfilaments

What would occur if CapZ was inhibited in cells?

Which of the following proteins is involved in formation of actin bundles in microvilli by providing crosslinks between actin filaments?

What contractile structure is essential for cell division?

Listeria is a bacterial parasite that has evolved unique ways to enter animal cells and then use actin polymerization for its intracellular movement.Which of the following statements is true in regards to Listeria and actin polymerization?

The plasma membrane of eukaryotic cells is supported by:

In the budding yeast S.cerevisiae,which of the following is NOT transported into the bud by myosin V?

Membrane extension during cell locomotion is driven by:

What cellular components cause some actin filaments to form bundles and others to form networks?

If the activity of thymosin β4 was inhibited in fibroblasts,the overall effect would be:

In response to a chemotactic signal,a cell forms structures to aid in locomotion.In lamellipodia,active Rac will stimulate F-actin polymerization at the leading edge via _____,whereas actin that will form stress fibers will be recruited by formin downstream of activation of this small GTPase _____.

What is the function of CapZ and tropomodulin in the sarcomere?

At ATP-G-actin concentrations that are intermediate between the Cc for the (+)end and the Cc for the (-)end,_____ will be observed.The Cc needed for elongation at the (+)end is _____ than that at the (-)end of actin microfilaments.

The correct order of events in cell locomotion is:

Within an actin filament,each actin subunit is surrounded by _____ neighboring actin subunits.

Human erythrocytes depend on microfilament networks to provide strength and flexibility.Describe this network and explain how microfilaments are attached to the plasma membrane in human erythrocytes.

What actin-binding protein mediates gel-sol transitions,and how is this protein's activity regulated?

All of the following statements about actin assembly are correct EXCEPT:

A well-coordinated mechanism involving cell-surface receptors and the actin cytoskeleton allows leukocytes to bind and engulf invading bacteria.Briefly describe how bacteria are phagocytosed.

The elastic Brownian ratchet model has been proposed to explain:

Chemical Foundations

Molecular Genetic Techniques

Protein Structure and Function

Culturing and Visualizing Cells

Fundamental Molecular Genetic Mechanisms

Bio-membrane Structure

Genes Genomics and Chromosomes

Transcriptional Control of Gene Expression

Post-Transcriptional Gene Control

Transmembrane Transport of Ions and Small Molecules

Cellular Energetics

Moving Proteins Into Membranes and Organelles

Vesicular Traffic, Secretion, and Endocytosis

Signal Transduction and G-Protein Coupled Receptors

Signaling Pathways That Control Gene Activity

Cell Organization and Movement II: Microtubules and Intermediate Filaments

Regulating the Eukaryotic Cell Cycle

Integrating Cells Into Tissues

Cell Birth, Lineage, and Death

Nerve Cells

Immunology

Cancer

Filters

In response to a chemotactic signal,a cell forms structures to aid in locomotion.In lamellipodia,active Rac will stimulate F-actin polymerization at the leading edge via _,whereas actin that will form stress fibers will be recruited by formin downstream of activation of this small GTPase _.

At ATP-G-actin concentrations that are intermediate between the Cc for the (+)end and the Cc for the (-)end,_ will be observed.The Cc needed for elongation at the (+)end is _ than that at the (-)end of actin microfilaments.