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Questions and Answers
Actin filaments are the primary cytoskeletal proteins in all cells, with a diameter of approximately 7 nm.
Actin filaments are the primary cytoskeletal proteins in all cells, with a diameter of approximately 7 nm.
True
Intermediate filaments are responsible for cell movements and muscle contraction.
Intermediate filaments are responsible for cell movements and muscle contraction.
False
The cytoskeleton is solely responsible for determining the position of organelles within the cytoplasm.
The cytoskeleton is solely responsible for determining the position of organelles within the cytoplasm.
False
Microtubules are involved in chromosome movement and cilia and flagella function.
Microtubules are involved in chromosome movement and cilia and flagella function.
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Cytoskeleton accessory proteins link the protein filaments to organelles and the plasma membrane.
Cytoskeleton accessory proteins link the protein filaments to organelles and the plasma membrane.
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Actin filaments are also known as microtubules.
Actin filaments are also known as microtubules.
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The assembly of actin filaments involves the polymerization of actin monomers.
The assembly of actin filaments involves the polymerization of actin monomers.
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Actin filaments have the same orientation at both ends.
Actin filaments have the same orientation at both ends.
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Actin bundles are formed from actin filaments arranged in orthogonal arrays.
Actin bundles are formed from actin filaments arranged in orthogonal arrays.
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Actin-bundling proteins are typically large flexible proteins.
Actin-bundling proteins are typically large flexible proteins.
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Study Notes
Cytoskeleton and Cellular Motility
- The cytoskeleton is a network of protein filaments throughout the cytoplasm of eukaryotic cells.
- It provides a structural framework for the cell, determining cell shape and organizing organelles.
- The cytoskeleton is responsible for cell movements.
- The cytoskeleton is composed of three major protein filaments: actin filaments, intermediate filaments, and microtubules.
- Accessory proteins link these filaments to subcellular organelles and the plasma membrane.
Actin Filaments
- The major cytoskeletal protein in most cells
- Polymerizes into thin, flexible fibers (7 nm in diameter, up to several micrometers long).
- Abundant beneath the plasma membrane, forming a network for mechanical support, shape determination, and cell surface movement.
- Facilitates cell migration, engulfment, and division.
Structure and Organization of Actin Filaments
- Assembly and disassembly of actin filaments
- Actin filament organization
- Association of actin filaments with the plasma membrane
- Protrusions of the cell surface
Actin, Myosin, and Cell Movement
- Muscle Contraction
- Contractile assemblies of actin and myosin in nonmuscle cells
- Nonmuscle myosins
- Formation of protrusions and cell movement
Intermediate Filaments
- Intermediate filaments have diameters of 8-11 nm, intermediate between actin filaments (7 nm) and microtubules (25 nm).
- Not directly involved in cell movements; instead provide mechanical strength to cells and tissues.
- Composed of a variety of proteins expressed in different cell types.
- More than 65 different intermediate filament proteins are identified and classified into six groups.
- Function in various cells, such as epithelial, muscle, and nerve cells.
Structure of Intermediate Filament Proteins
- Contain a central a-helical rod domain (approximately 310 amino acids).
- N-terminal head and C-terminal tail domains vary in size and shape.
Assembly of Intermediate Filaments
- Polypeptides wind around each other to form dimers.
- Dimers associate in a staggered antiparallel fashion forming tetramers.
- Tetramers to form protofilaments.
- Eight protofilaments weave around each other forming a rope-like structure.
Intracellular Organization of Intermediate Filaments
- Form an elaborate network in the cytoplasm, extending from a ring surrounding the nucleus to the plasma membrane.
- In epithelial cells, intermediate filaments are anchored at specialized cell contacts.
- Play specialized roles in muscle and nerve cells
- Involved in cell structure by providing mechanical strength.
Microtubules
- Rigid hollow rods (approximately 25 nm in diameter).
- Dynamic structures constantly assembling and disassembling.
- Function in cell shape determination, various cell movements (e.g., cell locomotion), intracellular transport, and chromosome separation during mitosis.
Assembly of Microtubules (in animal cells)
- Most microtubules extend outward from the centrosome, a structure near the nucleus.
Structure and Dynamic Organization of Microtubules
- Composed of a single type of globular protein, tubulin.
Structure of Microtubules
- Composed of tubulin dimers (consisting of alpha and beta tubulin).
- Polymerize into 13 protofilaments arranged in a hollow cylinder structure.
- Contain a y-tubulin that plays a critical role in initiating microtubule assembly within the centrosome.
Microtubule Motors and Movement
- Microtubules are responsible for intracellular transport of organelles, and the beating cilia and flagella.
- Movement is driven by motor proteins that utilize energy from ATP hydrolysis.
Cargo Transport and Intracellular Organization
- Microtubules are crucial for transporting macromolecules, membrane vesicles, and organelles throughout the cytoplasm of eukaryotic cells.
Reorganization of Microtubules during Mitosis
- Microtubules reorganize to form the mitotic spindle during mitosis.
- Spindle is important in chromosome separation process.
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Description
Explore the structure and function of the cytoskeleton, focusing on actin filaments and their role in cellular motility. This quiz covers the composition, organization, and dynamics of cytoskeletal components that contribute to cell shape and movement. Test your knowledge on the intricate connections between these protein filaments and cellular processes.
