treadmillingilmiönä

The treadmilling phenomenon, also known as treadmilling effect, describes a process observed in dynamic filament structures within cells, most notably actin filaments and microtubules. It refers to the observation that these filaments can simultaneously grow at one end and shrink at the other, resulting in a net flux of polymer subunits through the filament without a change in its overall length.

In the context of actin filaments, treadmilling occurs when actin monomers, specifically ATP-bound actin, add to the barbed (plus) end of the filament. Simultaneously, at the pointed (minus) end, ADP-bound actin monomers are released. This differential rate of addition and removal leads to a directional movement of the filament, although its length remains relatively constant. This process is crucial for various cellular functions, including cell motility, muscle contraction, and cytokinesis.

Similarly, microtubules exhibit treadmilling. Tubulin dimers, in their GTP-bound form, add to the plus end, while GDP-bound tubulin is hydrolyzed and dissociates from the minus end. The rate of GTP hydrolysis within the microtubule lattice influences the stability of the filament and can lead to dynamic instability, where microtubules can rapidly grow or shrink. Treadmilling in microtubules plays a role in cell division, intracellular transport, and maintaining cell shape. The concept of treadmilling highlights the dynamic and ever-changing nature of cytoskeletal components within living cells.