Spindle fibres are formed of microtubules, which play a important role in movement of chromosomes and centrioles during cell division. Biochemically a profilament of microtubule is made of a protein called tubulin. Tubulin is an acidic protein which occurs in two different forms called a-tubulin and p tubulin. Cytoplasmic microtubules are highly dynamic structures constantly forming and dis-appearing depending on cell activities. Myosin is fibrous functional protein of muscle. Myoglobin protein of muscle cells act as a reservoir of oxygen.