Lodish Ch 17: Cell Organization and Movement I

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Questions and Answers

The plasma membrane of eukaryotic cells is supported by:

lamins

microtubules

actin filaments (correct)

intermediate filaments

Three major groups of filament systems comprising the cytoskeleton are all composed of polymers of assembled subunits, which vary in thickness when assembled. Which is the correct order, from smallest to largest, of the filament systems?

microtubules, microfilaments, intermediate filaments

intermediate filaments, microtubules, microfilaments

microfilaments, microtubules, intermediate filaments

none of the above (correct)

Actin-binding proteins that generate actin filament bundles:

are long and flexible

can also bundle microtubules

are short and inflexible (correct)

bind only to the ends of actin filaments

Decoration of actin filaments with myosin S1 is commonly used to:

reveal the polarity of actin filaments Signup and view all the answers

Many actin cross-linking proteins contain:

a CH domain Signup and view all the answers

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.

treadmilling, lower Signup and view all the answers

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

actin (-) ends assemble more rapidly than actin (+) ends Signup and view all the answers

Gelsolin is activated by:

Ca²⁺ binding Signup and view all the answers

During treadmilling, actin subunits add:

predominantly to filament (+) ends Signup and view all the answers

Which of the following proteins promotes actin assembly and is involved in signaling pathways controlling actin assembly at the plasma membrane?

profilin Signup and view all the answers

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?

Listeria ActA binds VASP, which enhances ATP-actin assembly Signup and view all the answers

Which of the following is a G-actin sequestering protein that allows cells to maintain a relatively high G-actin concentration in cells?

thymosin β4 Signup and view all the answers

Cofilin:

cleaves actin by twisting adjacent F-actin monomers in the filament Signup and view all the answers

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

an increase in cell locomotion because there would be a higher concentration of actin available Signup and view all the answers

The two proteins that play the most important role in actin microfilament elongation are:

profilin and thymosin β4 Signup and view all the answers

What would occur if CapZ was inhibited in cells?

increased steady-state treadmilling of F-actin Signup and view all the answers

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

fimbrin Signup and view all the answers

How do the different types of actin-binding proteins relate to the ability of actin to form bundles and networks?

Proteins promoting bundle formation tend to be short and inflexible, whereas proteins that promote network formation tend to be longer and more flexible Signup and view all the answers

Which region of myosin interacts with actin filaments?

the head domain Signup and view all the answers

Which of the following properties is not shared by all myosins?

the ability to form dimers Signup and view all the answers

All myosins move toward the (+) end of actin filaments EXCEPT:

myosin VI Signup and view all the answers

In the operational model for movement of myosin along an actin filament, the power stroke occurs during:

release of phosphate (Pi) Signup and view all the answers

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

to maintain a constant actin thin filament length Signup and view all the answers

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

nucleus Signup and view all the answers

Multinucleated cells may result from a defect in:

myosin II Signup and view all the answers

Which of the following is NOT a function of myosin-powered movements?

flagellum-mediated cell motility Signup and view all the answers

Membrane extension during cell locomotion is driven by:

actin polymerization Signup and view all the answers

Lamellipodia are located:

at a moving cell's leading edge Signup and view all the answers

The elastic Brownian ratchet model has been proposed to explain:

membrane extension Signup and view all the answers

Small G proteins, including Rho, Rac, and Cdc42, contribute to the coordinated movement and overall polarity of a migrating cell. Assuming that the cell is migrating in a left-to-right fashion, which of the following is correct?

active Cdc42 at the leading edge of the cell and active Rho at the back of the cell Signup and view all the answers

The correct order of events in cell locomotion is:

rear focal adhesion, membrane protrusion, front focal adhesion, cell body translocation, de-adhesion Signup and view all the answers

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

Arp 2/3; Rho Signup and view all the answers

In a scratch wound assay, cells are treated with inhibitors of Rho kinase. What would be observed?

The distance the cells migrate into the scratch is small, and actin staining reveals stress fibers, lamellipodia, and filapodia Signup and view all the answers

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

four Signup and view all the answers

Study Notes

Cell Organization and Movement I: Microfilaments

Eukaryotic cell plasma membranes are supported by actin filaments.
Cytoskeletal filament systems include microtubules, microfilaments, and intermediate filaments. The correct order from smallest to largest is: microfilaments, microtubules, intermediate filaments.
Actin filament bundles are generated by actin-binding proteins. These proteins are short and inflexible.
Myosin S1 decoration of actin filaments is used to attach actin filaments to cell membranes.
Actin cross-linking proteins frequently contain a CH domain.
Within an actin filament, each actin subunit is surrounded by four neighboring actin subunits.
Actin filaments appear as twisted strings of beads with a diameter of 7-9 nm when viewed by negative stain electron microscopy.
Actin filament networks and bundles are created by different actin-binding proteins (ABPs). Bundling proteins tend to be short and inflexible, whereas networking proteins tend to be longer and more flexible.
ATP-G-actin concentrations intermediate between the Cc for the (+) end and the Cc for the (-) end of microfilaments result in treadmilling which is the observable growth and shrinking effect.
Actin assembly is correct except that actin (-) ends do not assemble more quickly than actin (+) ends.
Gelsolin activation occurs through Ca²⁺ binding.
Treadmilling predominantly adds actin subunits to the (+) end of a filament.
Actin assembly is promoted, and the signaling pathways for actin assembly at the plasma membrane are influenced by a protein.
Listeria uses actin polymerization for intracellular movement. The Listeria ActA protein enhances ATP-actin assembly by binding to VASP.
Gelsolin severs actin filaments and caps (+) ends of the resulting pieces and is activated by Ca²⁺ binding.
Thymosin ẞ4 sequesters G-actin to maintain a high G-actin concentration in cells.
Leukocytes engulf bacteria through a coordinated mechanism involving cell-surface receptors and the actin cytoskeleton. The antibodies recognize the bacterial surface proteins and bind, followed by a recruitment of actin networks at the site, resulting eventually in the bacteria becoming completely engulfed and degraded.
G-actin sequestering proteins help maintain high G-actin concentrations in cells, and the key protein is thymosin ß4.
The head domain of myosin binds to actin, tail domains bind to other molecules, and the neck domain regulates the activity of the head domain.
The power stroke of myosin movement along an actin filament occurs during the release of phosphate (Pi).
CapZ and tropomodulin center the myosin thick filaments and maintain a constant actin thin filament length in sarcomeres.
Actin in erythrocytes is arranged in a fishnet structure and is linked to bicarbonate transporters and glycophorin C by ankyrin and band 4.1 protein, respectively.
Actin plays a key role in cell movement and shape change.
The head domain of myosin binds ATP, the neck domain coordinates the head domain's activity, and the tail domain binds cellular cargo.
Actin interactions are key mechanisms for cell locomotion and cell shape change.
Myosin binds actin and uses the energy from ATP hydrolysis to generate movement. Myosin tail domains bind cargo.
Lamellipodia are located at the leading edge of a moving cell.
Small G proteins (Rho, Rac, and Cdc42) coordinate cell movement and polarity.

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Explore the intricate details of microfilaments and their role in eukaryotic cell organization. This quiz covers the structure and function of actin filaments, the proteins involved, and their significance in cytoskeletal systems. Test your knowledge on actin dynamics and its applications in cellular movement.

Lodish Ch 17: Cell Organization and Movement I - Microfilaments

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