Tail - Structure of the Sperm

The tail or flagellum is the longest part of the sperm. By its movement it causes the sperm to swim with the head forward. It consists of a thin layer of cytoplasm surrounded by plasmalemma. The axial filament is the main part of the tail or flagellum. Its structure is essentially similar to a typical flagellum or cilium with the arrangement of 9 peripheral pairs and one central pair of longitudinal fibers. The major portion of the flagellum is called 'axoneme'. An axoneme is formed by the microtubules emerging out of the centriole at the base of sperm nucleus. The core of the axoneme consists of two central microtubules surrounded by a row of nine doublet microtubules. In fact, only one microtubule is complete having thirteen protofilaments; the other is C-shaped having only eleven protofilaments.  The protofilaments are exclusively made of the dimeric protein-tubulin. Another protein dynein is attached to microtubule. The dynein is capable of hydrolysing ATP molecule and can convert chemical energy into mechanical energy that propels the sperm.