Type II Myosins Function and Comparison

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Questions and Answers

What is the main function of myosin II in muscle contraction?

To break down actin filaments

To pull arrays of actin filaments together (correct)

To synthesize ATP

To transport vesicles over large distances

How do kinesin and myosin II move along protein filaments?

Through a repulsive force

Using a ladder-like mechanism

By hydrolyzing ATP to change their shape (correct)

By using a ratchet-like mechanism

What is the characteristic of muscle fibers?

Multinucleate, long, and thin (correct)

Multinucleate, short, and thin

Uninucleate, long, and thick

Uninucleate, short, and thin

What is the function of cross-bridges in muscle contraction?

To generate force for muscle contraction Signup and view all the answers

What is the result of the sliding filament model of muscle contraction?

Shortening of sarcomeres Signup and view all the answers

In which direction do myosin II molecules move along actin filaments?

Toward the plus ends Signup and view all the answers

What is the function of kinesin proteins?

To transport vesicles over large distances Signup and view all the answers

How far can a single myosin II molecule move an actin filament?

12-15 nm Signup and view all the answers

What type of actin structures are exhibited by microvilli?

Ordered actin structures Signup and view all the answers

Which protein links actin to membranes?

Spectrin Signup and view all the answers

What is the function of actin-membrane interactions?

Cell response to mechanical forces Signup and view all the answers

What is a characteristic of intermediate filaments (IFs)?

They are abundant in many animal cells Signup and view all the answers

What type of proteins are involved in forming actin networks?

Fimbrin and a-actinin Signup and view all the answers

What is the indirect connection between actin filaments and extracellular surfaces?

Via transmembrane proteins Signup and view all the answers

What is the effect of cytochalasins on microfilaments?

They prevent the addition of new monomers to existing microfilaments Signup and view all the answers

What is the role of latrunculin A in microfilament formation?

It sequesters actin monomers and prevents their addition to microfilaments Signup and view all the answers

What is the characteristic of actin in filopodia?

It forms highly oriented, polarized cables with the actin plus ends toward the tip of the protrusion Signup and view all the answers

What is the role of actin-binding proteins in regulating actin organization?

They control the assembly and structure of actin networks Signup and view all the answers

What is the function of α-actinin in filopodia?

It keeps the actin tightly bundled Signup and view all the answers

What is the characteristic of the cell cortex?

It has actin crosslinked into a gel of microfilaments Signup and view all the answers

What is the role of phalloidin in microfilament formation?

It stabilizes microfilaments and prevents their depolymerization Signup and view all the answers

Study Notes

Type II Myosins

Myosin II pulls arrays of actin filaments together, resulting in cell contraction
Resembles kinesin, with globular domains that walk along a protein filament, using ATP hydrolysis to change shape

Kinesins Versus Myosin

Kinesins transport vesicles over large distances, operating alone or in small numbers
A single myosin II molecule slides an actin filament about 12–15 nm
Myosin II molecules move short distances but operate in large arrays, mediating muscle contraction

Microfilament-Based Motility: Muscle Cells in Action

Muscle contraction is the most familiar example of mechanical work mediated by intracellular filaments
A muscle consists of parallel muscle fibers, each fiber being a long, thin, highly specialized, multinucleate cell
Each muscle fiber contains numerous myofibrils, divided along their length into repeating units called sarcomeres

The Sliding-Filament Model Explains Muscle Contraction

Myosin II moves toward the plus ends, so thick filaments move toward the Z lines during contraction (filaments remain same length)
The sliding filament model explains muscle contraction, where thin filaments slide past thick filaments, with no change in length of either
Cross-bridges form between F-actin of thin filaments and myosin heads of thick filaments, requiring lots of ATP to dissociate rapidly

Microfilament Organization and Dynamics

Cytochalasins prevent the addition of new monomers to existing microfilaments
Latrunculin A sequesters actin monomers and prevents their addition to microfilaments
Phalloidin stabilizes microfilaments and prevents their depolymerization
Actin-binding proteins regulate the organization of actin, controlling where actin assembles and the structure of resulting networks

Cells Can Dynamically Assemble Actin into a Variety of Structures

The cell cortex has actin crosslinked into a gel of microfilaments
Cells that adhere tightly to the underlying substratum have organized bundles called stress fibers
Lamellipodia have a branched network of actin
Filopodia have highly oriented, polarized cables with actin plus ends toward the tip of the protrusion

Actin-Binding Proteins Regulate Actin Organization

Cells use actin-binding proteins to control where actin assembles and the structure of the resulting network
Control occurs at the nucleation, elongation, and severing of microfilaments and at the association of microfilaments into networks

Proteins That Bundle Actin Filaments

α-Actinin and fascin/fimbrin are proteins that bundle actin filaments
Actin bundles in filopodia and microvilli are examples of ordered actin structures

Actin Networks and Membrane Interactions

Actin filaments indirectly connect to the plasma membrane and exert force on it
This connection requires one or more linking proteins, such as spectrin and ankyrin
Actin–membrane interactions allow cells to respond to mechanical forces

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Description

This quiz covers the function of type II myosins, their mechanism of contraction, and a comparison with kinesins. It explains how myosin II pulls actin filaments together and how it differs from kinesins in terms of function and transportation.