Dr Praveen Kumar Agrawal is teaching live on Unacademy Plus
Course: Locomotion and Movement -2 Lesson - 8:Structure and Chemistry of Actin filaments DR. P. K. AGRAWAL M.Sc, PH.D., CSIR NET (JRF), SRF, GATE, FIAZ 20 Years of Pre-medical teaching experience Ex Faculty, Allen Career Institute, Kota Watch my Live Classes on Unacademy Plus
STRUCTURE AND CHEMISTRY OF ACTIN FILAMENTS . Actin filaments are thin filaments, interdigitated with myosin filaments. These are light coloured Actin filaments are associated with the Z disc (line) and form the I band. Some of their part also remain penetrated into the A band, when the muscle is at rest. Each actin filament is a complex of contractile proteins that consists of three different components(i) F-actin, (ii) Tropomyosin and (ii) Troponin. (i) F-actin It forms the backbone of actin filament. It is a double stranded protein. Each strand is composed of polymerized G-actin molecules (Mol. Wt. 4200o) . One ADP molecule is attached to each G-actin molecule. These ADP molecules are the active sites of actin.
(ii) Tropomyosin The actin filament contains two additional protein strands, that are polymers of tropomyosin molecules (Mol. Wt. of each is 7o,ooo). Each strand is loosely attached to an F-actin strand. . In the resting stage, Tropomyosin physically covers the active sites of the actin strand, so that interaction can not occur between the actin and myosin to cause contraction (iii) Troponin . It is a complex of three globular proteins, which are attached approx, 2/3rd the distance along each The three globular proteins are- (a) Troponin-l (having strong affinity for actin) . (b) Troponin-T (it has affinity for tropomyosin) and . (c) Troponin-C (it has affinity for calcium ions) At relaxing condition, the troponin and tropomyosin together form TT complex, which covers the active sites of F actin. . The troponin complex is believed to attach the tropomyosin to the actin (The strong affinity of troponin for calcium ions is believed to initiate the contraction process).
Structure of mysin filament and chemistry of Actin molecule 0 G-actin F-actin Tropomyosin Troponin Complete actin filament
Active site of actin TT complex Covering the active site of actin actin filament Myosin filament
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