Question 1

Which of the following cytoskeletal filaments are abundant in an animal cell nucleus?

Accepted Answer

A)  Microfilaments 
B)  Microtubules 
C)  Septins 
D)  Intermediate filaments 
E)  Spectrin filaments 
A)  Microfilaments 
B)  Microtubules 
C)  Septins 
D)  Intermediate filaments 
E)  Spectrin filaments

Question 2

Indicate if each of the following changes occurring during mitosis in a fibroblast is the result of the reorganization of actin filaments (A), microtubules (M), or intermediate filaments (I). Your answer would be a five-letter string composed of letters A, M, and I only; e.g. AIAAM.
( )	The cell rounds up.
( )	The endoplasmic reticulum collapses.
( )	The Golgi apparatus fragments.
( )	The primary cilium is resorbed (disappears).
( )	The contractile ring forms and constricts.

Accepted Answer

The change in the organization of the

Question 3

In the presence of ATP in a flagellum, an axonemal dynein that is interacting through its tail with the A microtubule of a peripheral doublet can push this doublet toward the ...(1) of the flagellum, but due to the presence of linking proteins such as ...(2), this force is converted into a bending motion.

Accepted Answer

A)  (1) tip; (2) nexin 
B)  (1) base; (2) nexin 
C)  (1) tip; (2) nebulin 
D)  (1) base; (2) nebulin 
E)  (1) tip; (2) tau 
A)  (1) tip; (2) nexin 
B)  (1) base; (2) nexin 
C)  (1) tip; (2) nebulin 
D)  (1) base; (2) nebulin 
E)  (1) tip; (2) tau

Question 4

Indicate true (T) and false (F) statements below regarding the primary cilia. Your answer would be a four-letter string composed of letters T and F only, e.g. TFFF.
( )	Primary cilia are found on the surface of almost all cell types in our bodies.
( )	Primary cilia are motile.
( )	Primary cilia are made in interphase at basal bodies.
( )	Primary cilia are thought to function in sensing and responding to external signals.

Accepted Answer

Primary cilia are nonmotile

Question 5

How is membrane protrusion by blebbing different from that by lamellipodia?

Accepted Answer

A)  Blebbing usually occurs on a rigid substratum such as glass, whereas lamellipodia form on pliable substrata. 
B)  Blebbing is mostly observed in vitro, whereas lamellipodia are observed both in vitro and in vivo. 
C)  Blebbing does not involve myosin II activity, but formation of lamellipodia does. 
D)  Blebbing requires loss of membrane interaction with actin filaments, whereas lamellipodia require a close interaction between the two. 
E)  All of the above. 
A)  Blebbing usually occurs on a rigid substratum such as glass, whereas lamellipodia form on pliable substrata. 
B)  Blebbing is mostly observed in vitro, whereas lamellipodia are observed both in vitro and in vivo. 
C)  Blebbing does not involve myosin II activity, but formation of lamellipodia does. 
D)  Blebbing requires loss of membrane interaction with actin filaments, whereas lamellipodia require a close interaction between the two. 
E)  All of the above.

Question 6

Indicate if each of the following descriptions matches actin filaments (A), microtubules (M), or intermediate filaments (I). Your answer would be a four-letter string composed of letters A, M, and I only; e.g. AAMM.
( )	They form hollow structures with multiple lateral interactions.
( )	They form strong structures that are more resilient than the other two cytoskeletal filaments.
( )	Their subunits bind GTP and hydrolyze it.
( )	They form coiled-coil interactions between the subunits.

Accepted Answer

Microtubules form hollow tubes whose w

Question 7

The duty ratio for a motor protein is defined as the fraction of time in each cycle of activity of the motor in which the head is bound with high affinity to its cytoskeletal track. Which of the following is reasonable given this definition?

Accepted Answer

A)  Myosin V has a higher duty ratio than myosin II, because Pᵢ release is the rate-limiting step in its cycle. 
B)  Myosin II has a higher duty ratio than myosin V, because Pᵢ release is the rate-limiting step in its cycle. 
C)  Myosin V has a higher duty ratio than myosin II, because ADP release is the rate-limiting step in its cycle. 
D)  Myosin II has a higher duty ratio than myosin V, because ADP release is the rate-limiting step in its cycle. 
A)  Myosin V has a higher duty ratio than myosin II, because Pᵢ release is the rate-limiting step in its cycle. 
B)  Myosin II has a higher duty ratio than myosin V, because Pᵢ release is the rate-limiting step in its cycle. 
C)  Myosin V has a higher duty ratio than myosin II, because ADP release is the rate-limiting step in its cycle. 
D)  Myosin II has a higher duty ratio than myosin V, because ADP release is the rate-limiting step in its cycle.

Question 8

A small unique insert found near the end of the motor domain in myosin VI has been linked to the singular ability of this myosin to move toward the pointed end of actin filaments. If the unique insert is removed by genetic engineering, the resulting mutant myosin VI is a plus-end directed motor. This observation indicates that …

Accepted Answer

A)  the unique insert is necessary and sufficient for minus-end directionality. 
B)  the unique insert is necessary for motor activity. 
C)  the unique insert is necessary for plus-end directed directionality. 
D)  the unique insert is not sufficient for minus-end directionality. 
E)  None of the above. 
A)  the unique insert is necessary and sufficient for minus-end directionality. 
B)  the unique insert is necessary for motor activity. 
C)  the unique insert is necessary for plus-end directed directionality. 
D)  the unique insert is not sufficient for minus-end directionality. 
E)  None of the above.

Question 9

These proteins are found in the budding yeast Saccharomyces cerevisiae; they form "neck filaments" between a mother cell and its growing bud, and help polarize protein distribution between the two. These proteins ...

Accepted Answer

A)  can polymerize to form filaments and sheets. 
B)  bind GTP. 
C)  are also involved in contractile ring formation during cytokinesis in animal cells. 
D)  form filaments that are thought to be nonpolar. 
E)  All of the above. 
A)  can polymerize to form filaments and sheets. 
B)  bind GTP. 
C)  are also involved in contractile ring formation during cytokinesis in animal cells. 
D)  form filaments that are thought to be nonpolar. 
E)  All of the above.

Question 10

F-actin is not a straight polymer but can be considered a double-helical assembly. The two protofilaments twist around each other and cross over approximately every 13 actin subunits, and the subunits in each protofilament are repeated every 2.8 nm along the helix. F-actin is almost 8 nm wide. Different myosin motors have different "step lengths" on actin depending on their function. Which of the following step lengths would you expect to belong to a processive myosin motor that carries large cellular cargoes such as endocytic vesicles?

Accepted Answer

A)  About 2.8 nm 
B)  About 8 nm 
C)  About 13 nm 
D)  About 27 nm 
E)  About 36 nm 
A)  About 2.8 nm 
B)  About 8 nm 
C)  About 13 nm 
D)  About 27 nm 
E)  About 36 nm

Question 11

Skeletal muscle cells consume enormous amounts of ATP. From the following list, choose the two proteins that directly hydrolyze most of this ATP. Your answer would be a two-letter string composed of letters A to F only, in alphabetical order, e.g. AF.
A. Troponin complex
B. Ca2+-release channel
C. Myosin light chains
D. Myosin heavy chain
E. Myosin light-chain kinase
F. Sarcoplasmic reticulum Ca2+-pump

Accepted Answer

The filament sliding and calc

Question 12

Indicate true (T) and false (F) statements below regarding cytoskeletal motor proteins. Your answer would be a five-letter string composed of letters T and F only, e.g. TTTFF.
( )	All myosin motors move toward the plus end of actin filaments.
( )	All myosin motors move toward the minus end of actin filaments.
( )	All kinesin motors move toward the plus end of microtubules.
( )	All kinesin motors move toward the minus end of microtubules.
( )	All dynein motors move toward the minus end of microtubules.

Accepted Answer

Both plus-end directed and m

Question 13

Bacteria contain homologs of cytoskeletal filament subunits …

Accepted Answer

A)  except those of the intermediate filaments. 
B)  but these homologs are incapable of nucleotide binding and hydrolysis. 
C)  that are less diverse in their function relative to their eukaryotic counterparts. 
D)  that can have different functions to those of their eukaryotic counterparts. 
E)  that are dispensable for cell growth and proliferation. 
A)  except those of the intermediate filaments. 
B)  but these homologs are incapable of nucleotide binding and hydrolysis. 
C)  that are less diverse in their function relative to their eukaryotic counterparts. 
D)  that can have different functions to those of their eukaryotic counterparts. 
E)  that are dispensable for cell growth and proliferation.

Question 14

Indicate whether each of the following descriptions matches Cdc42 (C), Rac (R), or Rho (H) from the Rho family of monomeric GTPases. Your answer would be a three-letter string composed of letters C, R, and H only, e.g. HRR.
( )	It activates formin.
( )	It inhibits myosin II activity.
( )	When constitutively active, it induces the formation of many prominent stress fibers.

Accepted Answer

The Rho family proteins regu

Question 15

Persistence length for a cytoskeletal filament is the minimum filament length at which random thermal fluctuations are likely to cause it to bend. Which of the following comparisons are true, considering the persistence lengths of (a) an actin filament, (b) a bundle of cross-linked actin filaments, and (c) a microtubule?

Accepted Answer

A)  (a > b) and (a > c) 
B)  (a > b) and (a  c) 
D)  (a  b) and (b > c) 
A)  (a > b) and (a > c) 
B)  (a > b) and (a  c) 
D)  (a  b) and (b > c)

Question 16

You have used "optical tweezers" to study the mechanics of myosin movement in a newly discovered member of the myosin II subfamily. Your results indicate that each myosin exerts a force of about 3 pN along the length of the actin filament, and displaces the filament by about 10 nm in each cycle of ATP hydrolysis. Assuming that the free-energy change for ATP hydrolysis is -50 kJ/mol under your experimental conditions, what is the efficiency of the myosin motor in converting the free energy to mechanical work? Remember that under a constant force F (in newtons), work (W; in joules) is calculated as W = F × d, where d is displacement (in meters) in the direction of the force. Avogadro's number is approximately 6 × 10²³ molecules/mole. Write down your answer as a percentage with no decimals, e.g. 99%.

Accepted Answer

The work performed by one myosin head i

Question 17

In lamellipodia, actin polymerization is nucleated by ...(1), while depolymerization is catalyzed by ...(2).

Accepted Answer

A)  (1) formin; (2) gelsolin 
B)  (1) Arp 2/3 complex; (2) gelsolin 
C)  (1) formin; (2) cofilin 
D)  (1) Arp 2/3 complex; (2) cofilin 
E)  (1) formin; (2) capping protein 
A)  (1) formin; (2) gelsolin 
B)  (1) Arp 2/3 complex; (2) gelsolin 
C)  (1) formin; (2) cofilin 
D)  (1) Arp 2/3 complex; (2) cofilin 
E)  (1) formin; (2) capping protein

Question 18

The pathogen Listeria monocytogenes can hijack the actin cytoskeleton in human cells and spread inside the host. Indicate true (T) and false (F) statements below about this phenomenon. Your answer would be a four-letter string composed of letters T and F only; e.g. TTFF.
( )	The movement can be reconstituted in vitro by placing the bacteria in a mixture of actin, formin, gelsolin, and capping protein.
( )	Cofilin counteracts the movement by depolymerizing actin filaments.
( )	The actin filaments grow with their minus ends pointed toward the bacterium.
( )	The movement depends on myosin activity to transport the bacteria on the actin filaments.

Accepted Answer

The bacterium recruits and activates t

Question 19

Actin filaments that are held together by the cross-linking protein fimbrin are not contractile. This is probably because …

Accepted Answer

A)  the very weak cross-linking by this protein cannot convert myosin II activity into a coherent contraction. 
B)  fimbrin arranges the actin filaments in parallel bundles in which all the plus ends point to the same direction. 
C)  the very tight packing of actin filaments by this small protein excludes myosin II filaments and other large proteins. 
D)  fimbrin arranges the actin filaments into gel-like networks in which myosin II activity does not produce contraction. 
E)  fimbrin is a large protein that binds to several actin filaments and resists contraction. 
A)  the very weak cross-linking by this protein cannot convert myosin II activity into a coherent contraction. 
B)  fimbrin arranges the actin filaments in parallel bundles in which all the plus ends point to the same direction. 
C)  the very tight packing of actin filaments by this small protein excludes myosin II filaments and other large proteins. 
D)  fimbrin arranges the actin filaments into gel-like networks in which myosin II activity does not produce contraction. 
E)  fimbrin is a large protein that binds to several actin filaments and resists contraction.

Question 20

After an animal dies, its muscles start to stiffen before the decomposition of tissues relaxes the muscles again. Which of the following would you expect to explain this muscle stiffening (i.e. rigor mortis)?

Accepted Answer

A)  The myosin II heads in muscle fibers remain attached to actin filaments due to the absence of Ca²⁺ in these cells. 
B)  The ATPase activity of muscle myosin II is inhibited by the elevated Ca²⁺. 
C)  The myosin II heads in muscle cells remain attached to actin filaments due to the elevated Ca²⁺ in the muscle fibers. 
D)  Titin molecules unfold, preventing muscle relaxation. 
E)  The myosin II heads in muscle cells remain attached to actin filaments due to covalent cross-linking. 
A)  The myosin II heads in muscle fibers remain attached to actin filaments due to the absence of Ca²⁺ in these cells. 
B)  The ATPase activity of muscle myosin II is inhibited by the elevated Ca²⁺. 
C)  The myosin II heads in muscle cells remain attached to actin filaments due to the elevated Ca²⁺ in the muscle fibers. 
D)  Titin molecules unfold, preventing muscle relaxation. 
E)  The myosin II heads in muscle cells remain attached to actin filaments due to covalent cross-linking.

Which of the following cytoskeletal filaments are abundant in an animal cell nucleus?

How is membrane protrusion by blebbing different from that by lamellipodia?

The duty ratio for a motor protein is defined as the fraction of time in each cycle of activity of the motor in which the head is bound with high affinity to its cytoskeletal track. Which of the following is reasonable given this definition?

These proteins are found in the budding yeast Saccharomyces cerevisiae; they form "neck filaments" between a mother cell and its growing bud, and help polarize protein distribution between the two. These proteins ...

Bacteria contain homologs of cytoskeletal filament subunits …

In lamellipodia, actin polymerization is nucleated by ...(1), while depolymerization is catalyzed by ...(2).

Actin filaments that are held together by the cross-linking protein fimbrin are not contractile. This is probably because …

After an animal dies, its muscles start to stiffen before the decomposition of tissues relaxes the muscles again. Which of the following would you expect to explain this muscle stiffening (i.e. rigor mortis)?

Cells and Genomes

Cell Chemistry and Bioenergetics

Proteins

DNA, Chromosomes, and Genomes

DNA Replication, Repair, and Recombination

How Cells Read the Genome: From DNA to Protein

Control of Gene Expression

Analyzing Cells, Molecules, and Systems

Visualizing Cells

Membrane Structure

Membrane Transport of Small Molecules and the Electrical Properties of Membranes

Intracellular Compartments and Protein Sorting

Intracellular Membrane Traffic

Energy Conversion: Mitochondria and Chloroplasts

Cell Signaling

The Cell Cycle

Cell Death

Cell Junctions and the Extracellular Matrix

Cancer

Development of Multicellular Organisms

Stem Cells and Tissue Renewal

Pathogens and Infection

The Innate and Adaptive Immune Systems

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Exam 16: The Cytoskeleton

Which of the following cytoskeletal filaments are abundant in an animal cell nucleus?

How is membrane protrusion by blebbing different from that by lamellipodia?

The duty ratio for a motor protein is defined as the fraction of time in each cycle of activity of the motor in which the head is bound with high affinity to its cytoskeletal track. Which of the following is reasonable given this definition?

These proteins are found in the budding yeast Saccharomyces cerevisiae; they form "neck filaments" between a mother cell and its growing bud, and help polarize protein distribution between the two. These proteins ...

Bacteria contain homologs of cytoskeletal filament subunits …

In lamellipodia, actin polymerization is nucleated by ...(1), while depolymerization is catalyzed by ...(2).

Actin filaments that are held together by the cross-linking protein fimbrin are not contractile. This is probably because …

After an animal dies, its muscles start to stiffen before the decomposition of tissues relaxes the muscles again. Which of the following would you expect to explain this muscle stiffening (i.e. rigor mortis)?

Cells and Genomes

Cell Chemistry and Bioenergetics

Proteins

DNA, Chromosomes, and Genomes

DNA Replication, Repair, and Recombination

How Cells Read the Genome: From DNA to Protein

Control of Gene Expression

Analyzing Cells, Molecules, and Systems

Visualizing Cells

Membrane Structure

Membrane Transport of Small Molecules and the Electrical Properties of Membranes

Intracellular Compartments and Protein Sorting

Intracellular Membrane Traffic

Energy Conversion: Mitochondria and Chloroplasts

Cell Signaling

The Cell Cycle

Cell Death

Cell Junctions and the Extracellular Matrix

Cancer

Development of Multicellular Organisms

Stem Cells and Tissue Renewal

Pathogens and Infection

The Innate and Adaptive Immune Systems

Filters