Sejtváz

Sejtváz, or the cytoskeleton, is the complex network of protein filaments inside eukaryotic cells that provides mechanical support, determines cell shape, and organizes the cytoplasm. It consists of three major classes of polymers: microfilaments (actin), intermediate filaments, and microtubules. In addition, cells can contain other filament systems and cross-linking proteins that modulate the network’s properties.

Microfilaments are flexible, about 7 nanometers in diameter, and are primarily built from actin monomers. They form a dynamic cortex beneath the plasma membrane and drive processes such as cell movement, shape changes, and endocytosis. Microtubules are rigid, about 25 nanometers in diameter, and are formed from tubulin dimers. They provide tracks for vesicle transport, help position organelles, and form the spindle apparatus during cell division. Intermediate filaments, with varied protein composition (for example keratins, vimentin, desmin), offer tensile strength and structural stability, helping tissues withstand mechanical stress.

The cytoskeleton is highly dynamic, with continuous polymerization and depolymerization influenced by cellular signaling and energy from ATP or GTP hydrolysis. It is regulated by a wide array of actin-binding proteins, microtubule-associated proteins, and motor proteins such as myosin, kinesin, and dynein, which convert chemical energy into mechanical work.

Functions of the sejtváz include maintaining cell shape and mechanical integrity, organizing the cytoplasm, facilitating intracellular transport, enabling cell migration, and supporting cell division. It also interfaces with the plasma membrane and extracellular matrix through linker proteins, integrating mechanical signals with cellular pathways. Dysregulation of the cytoskeleton is associated with various diseases, including cancer metastasis and neurodegenerative disorders.