Questions and Answers
Clusters of myosin-II molecules bind to each other through their coiled-coil tails, forming a bipolar ____ filament from which the heads _____
Clusters of myosin-II molecules bind to each other through their coiled-coil tails, forming a bipolar ____ filament from which the heads _____
Clusters of myosin-II molecules bind to each other through their coiled-coil tails, forming a bipolar ____ filament from which the heads _____
myosin; project
What does myosin filament do?
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If actin filaments and ____ filaments are organized together in a bundle, the bundle can generate a _____ contractile force.
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What are the contractile units of muscle?
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____ discs at either end of the sarcomere are attachment points for the ___ ends of actin filaments.
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What are the centrally located thick filaments composed of?
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The thin vertical line running down the center of the thick filament bundle corresponds to the bare regions of the ____ filaments.
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What is the cytoskeleton?
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What are the three types of protein filaments that make up the cytoskeleton?
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What are intermediate filaments?
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What is the main function of intermediate filaments?
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Intermediate filaments are ______ fibers with a diameter of about 10 nm; they are made out of _____ intermediate filament proteins.
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Intermediate filaments form a meshwork called the ____ _____ just beneath the inner nuclear membrane.
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What are microtubules?
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Microtubules are made of the protein __________.
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Actin filaments are helical ______ of the protein actin.
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Actin filaments have a diameter of about ___ nm.
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What structures do actin filaments form?
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What is the function of microtubules in cell structure?
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How do microtubules grow?
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Microtubules are rigid and can ______ when stretched.
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What are the main types of motor proteins that move along microtubules?
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Cilia beat in a whiplike fashion to move _____ over the cell's surface.
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What is the primary function of myosin-I?
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How does ATP hydrolysis affect actin filament stability?
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During the process of ___________, actin monomers are added to the plus end of a filament while others are lost from the minus end.
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What initiates cell crawling?
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Microtubules in a cilium or flagellum are arranged in a "_ + _" array.
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What is the role of ciliary dynein?
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All cells express actin filaments.
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Study Notes
Cytoskeleton Overview
- The cytoskeleton is essential for eukaryotic cells to maintain shape, organize cellular components, and enable movement.
- Comprised of three types of protein filaments: intermediate filaments, microtubules, and actin filaments.
Intermediate Filaments
- Diameter: approximately 10 nm; made of fibrous intermediate filament proteins.
- Provides mechanical strength and distributes stress across epithelial tissues.
- Forms the nuclear lamina beneath the inner nuclear membrane.
- Very flexible and withstands deformation without rupturing.
- Assembles from monomers into dimers, then tetramers, and finally into ropelike structures.
Microtubules
- Hollow cylinders made from tubulin, typically 25 nm in diameter.
- More rigid than actin filaments and intermediate filaments; can rupture when stretched.
- One end anchored at centrosomes; involved in various cellular structures like cilia and flagella.
- Built from tubulin dimers (α-tubulin and β-tubulin) linked by noncovalent interactions to form protofilaments (13 per microtubule).
Actin Filaments
- Also called microfilaments; consist of helical polymers of actin protein with a diameter of about 7 nm.
- Highly flexible and organized into bundles and networks, primarily concentrated in the cell cortex.
- Provides structural support and facilitates movements, including cytoplasmic streaming and cell crawling.
Motor Proteins
- Kinesins: Move toward the plus end of microtubules, transporting cellular cargo.
- Dyneins: Move toward the minus end, involved in organelle positioning.
- Both motor proteins convert ATP hydrolysis to mechanical work for movement along filaments.
Cilia and Flagella
- Cilia are hairlike structures, about 0.25 µm in diameter, containing microtubules arranged in a 9+2 structure.
- Cilia function to either move substances over cell surfaces or propel single cells through fluids.
- Flagella are longer than cilia and allow for movement of cells like sperm.
- Movement results from microtubule bending due to dynein activity.
Actin Dynamics and Cell Movement
- Cell crawling involves processes driven by cortical actin.
- Key processes include protrusion of cell membrane, adhesion to surfaces, and rear contraction.
- Actin polymerization at the leading edge initiates movement, forming structures like lamellipodia and filopodia.
- Treadmilling refers to dynamic turnover, where actin monomers add to the plus end while losing from the minus end, maintaining a constant length.
Myosin Protein Types
- Myosin-I: Simplest motor protein, involved in vesicle transport and shaping plasma membrane.
- Myosin-II: Forms bipolar filaments for muscle contraction, slides actin filaments past each other.
- Muscle contraction is mediated by interactions between actin and myosin-II bundles, essential for sarcomere function.
Sarcomeres
- The functional units of muscle contraction, composed of actin and myosin filaments.
- Z discs serve as attachment points for actin filaments, while myosin filaments occupy the center.
- Contraction occurs through sliding of myosin filaments relative to actin, powered by ATP hydrolysis.
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Description
Test your understanding of key concepts in cell biology with this quiz on cytoskeleton and its components. Delve into the roles of intermediate filaments, microtubules, and actin in cellular structure and function. Perfect for students looking to reinforce their knowledge of eukaryotic cell organization.
