Cytoskeletal Components and Functions

Cytoskeletal Components and Functions

• Cytoskeleton: A network of protein filaments in eukaryotic cells, providing structural support, organizing organelles, and facilitating intracellular transport.
• Microtubules: Hollow tubes of α- and β-tubulin dimers, the largest cytoskeletal component. They maintain cell shape, guide intracellular transport, support cell division, and form cilia/flagella.
• Microfilaments (Actin filaments): Thin, flexible filaments of globular actin monomers. They are involved in cell shape and movement, muscle contraction, cytoplasmic streaming, and cell division.
• Intermediate filaments: Solid, unbranched filaments of various proteins like keratin, vimentin, and neurofilaments. They provide mechanical strength, form the nuclear lamina, and contribute to cell-cell junctions.

Cytoskeletal Proteins

• Tubulin: A protein dimer (α- and β-tubulin) that assembles into microtubules.
• Actin: A globular protein that polymerizes into microfilaments.
• Dynein: A microtubule-binding protein that generates sliding forces between microtubules, driving cilia and flagella movement.
• Kinesin: A microtubule motor protein that moves cargo away from the centrosome (+ end of microtubules).
• MAPs (Microtubule-associated proteins): Proteins that bind to microtubules, controlling stability and assembly.
• Tau: A MAP whose abnormal phosphorylation is linked to Alzheimer's disease.
• Spectrin: An actin-binding protein crucial for red blood cell membrane stability.
• Dystrophin: An actin-binding protein that links actin to the basal lamina in muscle.
• Myosin: A motor protein that interacts with actin filaments, generating force for muscle contraction and cellular movement.
• Plectin: A dimeric protein that forms cross-bridges between intermediate filaments and other cytoskeletal filaments.

Specialized Structures and Processes

• Centrosome: The major microtubule-organizing center (MTOC) in animal cells, near the nucleus, organizing cilia/flagella and the mitotic spindle.
• Cilia: Hair-like structures with microtubules arranged in a 9+2 pattern, moving fluids like mucus.
• Flagella: Longer, hair-like structures with microtubules arranged in a 9+2 pattern, enabling cell movement (like sperm).
• Basal body: Structure at the base of cilia and flagella acting as a microtubule-organizing center.
• Mitotic spindle: An organized microtubule structure during cell division, separating chromosomes.

Cytoskeletal-related Diseases and Processes

• Treadmilling: Continuous addition of actin monomers (+ end) and removal (- end), creating a seemingly-moving filament.
• Contractile ring: Actin-myosin structure forming during cytokinesis, dividing the cell.
• Circumferential belt: Actin bundles encircling epithelial cells, regulating cell shape.
• Neurofibrillary tangles: Tangled hyperphosphorylated tau protein, associated with neurodegenerative diseases like Alzheimer's.
• Cytoplasmic streaming: Directed bulk flow of cytoplasm in large plant cells, facilitated by actin filaments.
• Axonal transport: Movement of materials along neuron axons, using microtubules and kinesin/dynein.
• Hereditary spherocytosis: Genetic disorder causing fragile, spherical red blood cells due to spectrin defects.
• Muscular dystrophy: Muscle wasting due to dystrophin defects.

Toxins and Their Effects on Cytoskeleton

• Amanita phalloides (Death Cap): A mushroom producing toxins (phalloidin) that inhibits RNA polymerase II and binds actin filaments.
• Phalloidin: A toxin binding tightly to actin filaments.
• Taxol (Paclitaxel): A drug binding to tubulin, stabilizing microtubules and preventing their depolymerization.