cytoskellet

Cytoskellet, or the cytoskeleton, is a dynamic network of protein filaments that extends throughout the cytoplasm of most eukaryotic cells. It provides shape and mechanical support, organizes the internal contents of the cell, and enables movement and transport at the cellular level. The cytoskeleton comprises three main filament types: microfilaments (actin filaments, about 7 nm in diameter), intermediate filaments (about 10 nm), and microtubules (about 25 nm).

Actin filaments are involved in cell motility, changes in cell shape, and endocytosis and exocytosis. Intermediate filaments confer tensile strength and help cells withstand mechanical stress. Microtubules form a dynamic scaffold that positions organelles, organizes the cell interior, and serves as tracks for motor proteins in vesicle transport and chromosome segregation during mitosis.

Motor proteins drive movement along the cytoskeleton. Myosin moves along actin filaments, powering muscle contraction and other cellular movements. Kinesin and dynein move along microtubules, transporting cargo and contributing to spindle dynamics during cell division. All three filament systems are highly dynamic, with rapid assembly and disassembly that allow the cell to remodel its architecture as needed.

Organizational centers include microtubule organizing centers, such as the centrosome in many animal cells, which nucleate microtubules during cell division. Plants and some other organisms organize microtubules differently. The cytoskeleton also interacts with the plasma membrane and organelles through linker proteins, contributing to cell polarity and signaling. Evolutionarily, eukaryotes possess complex cytoskeletal systems, while some bacterial and archaeal lineages harbor homologous components.