axonémának

An axoneme is a stable structure formed by microtubules that is found in eukaryotic cilia and flagella. It is the core structural component responsible for the motility of these appendages. The arrangement of microtubules within the axoneme is highly conserved and follows a characteristic 9+2 pattern. This pattern consists of nine pairs of microtubules arranged in a ring around the periphery, with a single pair of single microtubules located in the center. Each peripheral pair is a doublet, meaning it comprises two fused microtubules. The central pair consists of two individual microtubules.

The movement of cilia and flagella, and thus the cell, is generated by the sliding of these microtubules past each other. This sliding is powered by the motor protein dynein, which is attached to the outer microtubule doublets. Dynein molecules bind to one doublet and walk along the adjacent doublet, causing them to slide. However, the axoneme is a rigid structure, so this sliding is converted into bending. Specialized proteins called nexin link the outer doublets together, restricting the degree of sliding and forcing the axoneme to bend. The coordinated action of these dynein motors and linking proteins results in the characteristic whip-like motion of cilia and flagella, enabling processes such as locomotion in microorganisms or the movement of mucus in the respiratory tract. The precise organization and function of the axoneme are crucial for cellular mobility and have been conserved throughout evolution.