Thin filament is mainly composed of?

ANSWER: (A) ActinREF: Guyton's physiology 22nd edition page 72-76, Textbook Of Medical Physiology by Khurana page 90Indirect repeat from December 2009Repeat (**)CONTRACTILE APPARATUS:The contractile apparatus of the striated muscle are made up of three types of proteins:I Contractile proteins are actin and myosin that interacts to generate contractile force in a muscle.II Regulatory proteins also called relaxation proteins include tropomyosin and troponin. These regulate the interaction between actin and myosin.III. Anchoring protein, as the name indicates anchors different protein to each other as well as to sarcolemma and extracellular matrix. These includes a-actinin, titin, nebulin, dystrophin.THE FILAMENTS OF MUSCLE FIBRE:Thin filament: Each thin filament is made up of contractile protein actin and two regulatory proteins; troponin and tropomyosin.The thick filaments, which are about twice the diameter of the thin filaments, are made up of myosin. The thick filaments are lined up to form the A bands, whereas the array of thin filaments forms the less dense I bands. The lighter H bands in the center of the A bands are the regions where, when the muscle is relaxed, the thin filaments do not overlap the thick filaments. The Z lines transect the fibrils and connect to the thin filaments. If a transverse section through the A band is examined under the electron microscope, each thick filament is seen to be surrounded by six thin filaments in a regular hexagonal pattern.