filamendid

Filaments, or filamendid in Estonian, are slender, thread-like structures found in cells and some microorganisms. They are built mainly from protein polymers and form part of the cytoskeleton, providing shape and mechanical resilience to cells, guiding movement, and enabling intracellular transport. Filaments vary in composition and function, but are commonly grouped into cytoskeletal filaments and filamentous structures in microbes.

The main cytoskeletal filaments are actin filaments, microtubules, and intermediate filaments. Actin filaments are among the thinnest, with a diameter of about 7 nanometers, and are crucial for changing cell shape, enabling cell movement, and driving cytokinesis. Microtubules are thicker, about 25 nanometers in diameter, and form a dynamic internal scaffold that organizes the cell, serves as tracks for motor proteins, and is essential during cell division. Intermediate filaments, ranging roughly from 8 to 12 nanometers in diameter, provide mechanical strength and help maintain cell and tissue integrity under stress.

Filaments also occur in bacteria and some archaea, where actin- and tubulin-like proteins (such as MreB and FtsZ) coordinate cell wall synthesis, shape, and division. This highlights the evolutionary conservation of filament-based mechanisms across life.

Research and visualization of filaments employ light and electron microscopy. Fluorescent labeling (for example, using phalloidin to stain actin) enables visualization of filament networks in living or fixed cells, while electron microscopy reveals detailed ultrastructure.

Etymology traces the word to Latin filum, meaning thread. Filaments are central to numerous cellular processes and remain a major focus in cell biology and microbiology.